Patent Publication Number: US-2007109218-A1

Title: Display apparatus and display element driving method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2005-330618, filed on Nov. 15, 2005; the entire contents of which are incorporated herein by reference.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a display apparatus that drives a display element using an electrochemical luminescent material so as to perform luminous display, and a display element driving method.  
      2. Description of the Related Art  
      As display apparatuses like liquid crystal display apparatuses that utilize display elements for enabling luminous display in a cell structure containing a liquid crystal, display apparatuses that utilize electrochemical luminescence (ECL) elements are preset. As disclosed in JP-A No. 2002-324401 (KOKAI), the ECL elements are constituted so that an electrochemical luminescent material (ECL material) and electrolyte are disposed between two electrodes. The ECL material emits light by reacting ion radical species having different polarities which are generated by electrochemical oxidation or reduction. When a voltage is applied to the ECL element so as to drive it, the ECL material emits light by itself so that the ECL element performs luminous display.  
      In a method of driving such an ECL element, generally an applied voltage is precipitously raised at the time of emission of light, that voltage is maintained for a constant period of time, the voltage is repeatedly dropped to zero precipitously at the time of extinction, and the voltage is applied to the ECL element so that a voltage waveform is a rectangular waveform.  
      Further, as display apparatuses such as mobile telephones which are used in the open air and in doors, semi-transmission type LCDs which enable both reflection display and luminous display are proposed. As disclosed in JP-A No. 2003-241188 (KOKAI) for example, in the semi-transmission type LCDs, a convexo-concave reflection layer is provided to a part of a pixel in order to perform reflection display for reflecting an external light beam so as to display a pixel. Further, a transmissive display unit is provided to another area in order to perform luminous display in which transmission of a light beam from back light is controlled and the light beam is led to the outside, and the back light is provided below the transmissive display unit.  
      In the method for enabling both the reflection display and the luminous display, the luminous display can be performed sufficiently bright and clearly depending on brightness of the back light. The reflection display, however, is subject to a restraint of liquid crystal display principle such as use of a polarizing plate and a restraint of a display area such that one pixel is divided into two areas for the reflection display and the luminous display. For this reason, clear display having sufficient contrast cannot be obtained. Since the polarizing plate is used, the utilization efficiency of the light decreases by half.  
      On the other hand, as display apparatuses that enable the reflection display with high contrast, electrochromic display apparatuses (ECD) are present. As disclosed in JP-A No. 2003-021848 (KOKAI) for example, such display apparatuses are constituted so that a colored substance (EC material), which are discolored, separated out or dissolved due to electrochemical oxidation or reduction, and electrolyte are disposed between two electrodes. Since ECD, however, performs only the reflection display, the display is hardly seen in dark places.  
      In the conventional methods of driving the ECL element, a phenomenon that luminance remarkably reduces after the voltage is applied occurs, and thus the display with high luminance cannot be obtained stably for a long period of time.  
      It is desired to provide a display apparatus which is not subject to the restraint of the display area per one pixel, performs clear display with sufficient contrast even in dark places and enables both the reflection display and the luminous display, and to stably obtain the display with high luminance for a long period of time in this display apparatus.  
     SUMMARY OF THE INVENTION  
      According to one aspect of the present invention, a display apparatus includes a display element that includes an electrolyte solution layer containing an electrochemical luminescent material; and a voltage applying unit that applies a voltage with a waveform having a gradient for a first period and a flat top for a second period following the first period, to the electrolyte solution layer, so that the electrochemical luminescent material emits light.  
      According to another aspect of the present invention, a display apparatus includes a first layer that includes an electrochemical luminescent material; a second layer that includes an electrochromic material which is located so as to be opposed to at least a part of the first layer; a first voltage applying unit that applies a voltage to the first layer so that the electrochemical luminescent material emits light; a second voltage applying unit that applies a voltage to the electrochromic material to change a color of the electrochromic material; and a switching unit that selectively operates the first voltage applying unit and the second voltage applying unit.  
      According to still another aspect of the present invention, a method of driving a display element that includes an electrolyte solution layer containing an electrochemical luminescent material includes gradually increasing a voltage to be applied to the electrolyte solution layer up to a predetermined level; and maintaining the voltage of the predetermined level so that the electrochemical luminescent material emits light.  
      According to still another aspect of the present invention, a method of driving a display element that includes a first layer containing an electrochemical luminescent material and a second layer containing an electrochromic material and located so as to be opposed to at least a part of the first layer includes selectively executing a first voltage applying step and a second voltage applying step. The first voltage applying step includes applying a voltage to the first layer so that the electrochemical luminescent material emits light, and the second voltage applying step includes applying a voltage to the second layer to change a color of the electrochromic material. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a schematically explanatory diagram showing one example of a display element to be a display cell of a pixel of a display apparatus and a power supply circuit according to a first embodiment;  
       FIG. 2  is a circuit diagram showing an example in which a low-pass filter (LPF) is used in order that a waveform of a voltage between a first electrode and a second electrode becomes trapezoidal;  
       FIG. 3  is an explanatory diagram showing the display element and a circuit configuration of a driving unit when the second electrode is divided into a plurality of portions;  
       FIG. 4  is an explanatory diagram showing a waveform of an AC voltage to be applied to the display element of the display apparatus according to the first embodiment;  
       FIG. 5  is an explanatory diagram showing a waveform of a DC voltage to be applied to the display element of the display apparatus according to the first embodiment;  
       FIG. 6A  is an explanatory diagram showing a waveform of an AC voltage to be applied to the display element of a conventional display apparatus;  
       FIG. 6B  is an explanatory diagram showing a waveform of a DC voltage to be applied to the display element of a conventional display apparatus;  
       FIG. 7  is an explanatory diagram showing comparison between light emitting states of the display elements in the display apparatus according to the first embodiment and the conventional display apparatus;  
       FIG. 8  is a schematically sectional view showing one example of a configuration of the display element of the pixel in the display apparatus according to a second embodiment;  
       FIG. 9  is a schematically sectional view showing one example of a configuration of the pixel element in the display apparatus according to a first modified example of the second embodiment;  
       FIG. 10  is a schematically sectional view showing one example of the pixel element in the display apparatus according to a second modified example of the second embodiment;  
       FIG. 11  is a schematically sectional view showing one example of the pixel element in the display apparatus according to a third modified example of the second embodiment;  
       FIG. 12  is a sectional view schematically showing the display element to be the display cell in the display apparatus according to a third embodiment;  
       FIG. 13  is a sectional view schematically showing the display element to be the pixel in the display apparatus according to a fourth embodiment;  
       FIG. 14  is a sectional view schematically showing the display element to be the pixel in the display apparatus according to the fourth embodiment;  
       FIG. 15 a  sectional view schematically showing the display element to be the display cell in the display apparatus according to a fifth embodiment;  
       FIG. 16  is a sectional view schematically showing the display element to be the display cell in the display apparatus according to a modified example of the fifth embodiment;  
       FIG. 17  is a sectional view schematically showing the display element to be the display cell in the display apparatus according to a sixth embodiment;  
       FIG. 18  is a sectional view schematically showing the display element to be the display cell in the display apparatus according to a modified example of the sixth embodiment;  
       FIG. 19  is a sectional view schematically showing the display element to be the display cell in the display apparatus according to a seventh embodiment;  
       FIG. 20  is a sectional view schematically showing the display element to be the display cell in the display apparatus according to a modified example of the seventh embodiment;  
       FIG. 21  is a sectional view schematically showing the display element to be the display cell in the display apparatus according to an eighth embodiment;  
       FIG. 22  is a sectional view schematically showing the display element to be the display cell in the display apparatus according to a modified example of the eighth embodiment;  
       FIG. 23  is a sectional view schematically showing the display element to be the display cell in the display apparatus according to a ninth embodiment;  
       FIG. 24  is a sectional view schematically showing the display element to be the display cell in the display apparatus according to a tenth embodiment;  
       FIG. 25  is a sectional view schematically showing the display element to be the display cell in the display apparatus according to a modified example of the tenth embodiment;  
       FIG. 26  is a sectional view schematically showing the display element to be the display cell in the display apparatus according to an eleventh embodiment;  
       FIG. 27  is a plan view showing a part (portion of 2×2) of an arrangement of the pixels in the display apparatus according to the first embodiment; and  
       FIG. 28  is a plan view showing a part (portion of 2×2) of an arrangement of the pixels in the display apparatus according to the second to eleventh embodiments. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      A display apparatus according to a first embodiment includes arrangement of pixels having display cells L i,j , L i+1,j , L i,j+1 , and L i+1,j+1 . Display apparatuses according to second to eleventh embodiments also have the similar configuration.  FIG. 1  is a schematically explanatory diagram showing one example of a configuration of the display element L i,j  to be a display cell of a pixel X i,j  in the display apparatus according to the first embodiment and a configuration of a power supply circuit, where i=1 to n, j=1 to m, and n and m are positive integers. In  FIG. 1 , the configuration of the display element L i,j  is illustrated as a sectional view.  
      As shown in  FIG. 1 , the display element L i,j  in this embodiment has a first electrode  203  formed on a substrate  201 , a second electrode  204  formed on a substrate  202  so as to be opposed to and separated from the first electrode  203 , a spacer  206  which is installed securely to an end of the substrate  201  and an end of the substrate  202 , and an electrolyte solution layer  205  in a sealed cell formed by the two substrates  201  and  202  and the spacer  206 .  
      The first electrode  203  and the second electrode  204  are constructed in the sealed cell formed by the two substrates  201  and  202  and the spacer  206 .  
      The electrolyte solution layer  205  is formed by an electrolyte solution containing an electrochemical luminescent material (ECL material) for emitting light due to the electrolyte solution, electrochemical oxidation or reduction. That is, as to the electrolyte solution, the electrolyte includes the electrochemical luminescent material (ECL molecules) as a luminescent material for emitting light due to electrochemical oxidation or reduction. The electrolyte is a liquid or a solid which can realize ECL light emission, and is normally composed of supporting electrolyte and organic solvent. The electrolyte is not limited to the supporting electrolyte and the organic solvent, and thus may be a liquid or a solid which improves oxidation and reduction of luminescent molecules. The luminescent molecules is oxidized near the electrodes so as to become radical cation and is reduced to become radical anion. When both the radical cation and the radical anion associate with each other and disappear, an exciting state of the luminescent material is generated, and light is emitted at the deactivation process.  
      Examples of the supporting electrolyte to be used as the electrolyte solution are tetrabutylammonium perchlorate, potassium hexafluorophosphate, lithium trifluoromethane sulfonate, lithium perchlorate, tetrafluoroboric tetra-n-butylammonium, tripropylamine, and tetra-n-butylammonium fluoroborate.  
      Examples of the solvent are acetonitrile, N,N-dimethylform-amide, propylene carbonate, o-dichlorobenzene, glycerin, water, ethyl alcohol, propyl alcohol, dimethyl carbonate, ethylene carbonate, γ-butyrolactone, N-methylpyrrolidone (NMP), 2-methyltetrahydrofuran, 1,2-dimethoxyethane, toluene, tetrahydrofuran, benzonitrile, cyclohexane, n-hexane, acetone, nitrobenzen, 1,3-dioxolan, furan and benzotrifluoride.  
      Examples of the ECL material are a naphthacene derivative (rubrene, 5,12-diphenyl naphthacene), an anthracene derivative (9,10-diphenyl anthracene), a pentacene derivative (6,10-diphenyl pentacene), a poly-para-phenylene vinylene derivative, a polythiophene derivative, a poly-para-phenylene derivative and a polyfluorene derivative as pi-conjugated polymer, coumalin as heteroaromatic compound, Ru (bpy) 32 as a chelate metallic complex, tris(2-phenylpyridine) iridium as organic metal compound, a chelate lanthanoids complex.  
      At least one of the substrate  201  formed with the first electrode  203  and the substrate  202  formed with the second electrode  204  is normally a display unit as an observation surface of the display element. For this reason, the substrate to be the display unit is formed by an optically-transparent material. Examples of the optically-transparent material are preferably materials with less absorption in a visible light region including inorganic materials such as glass and organic materials such as optically-transparent resin. More specific examples are polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyether sulfone (PES), and polycarbonate (PC).  
      In order to enable display by the electrolyte solution layer  205  to be observed, one of the first electrode  203  and the second electrode  204 , which is positioned between the electrolyte solution layer  205  and the substrates to be the display unit, is formed by an optically-transparent material. Examples of such an optically-transparent material are oxides of transition metal such as oxides of titanium, zirconium, hafnium, strontium, zinc, tin, indium, yttrium, lanthanum, vanadium, niobium, tantalum, chromium, molybdenum and tungsten, perovskite such as SrTiO 3 , CaTiO 3 , BaTiO 3 , MgTiO 3  and SrNb 2 O 6 , and their compound oxide, their oxide mixture, and GaN as metal oxide semiconductor. Further, the electrode formed on the substrate which does not become the display unit does not have to be formed by the optically-transparent material, and thus an arbitrary conductive material can be used. A material with high reflectivity such as Al or Ag is used as the electrode formed on the substrate which does not become the display unit and a conductive material with high light transmission property is used as the electrode formed on the substrate to be the display unit. As a result, the luminous display of the display element can be preformed more brightly and clearly.  
      A power supply circuit  210  is connected to the first electrode  203  and the second electrode  204  of the display element L i,j  having the above configuration. The power supply circuit  210  is composed of a counter voltage generating circuit  221 , a signal voltage generating circuit  212 , a variable resistor  213  and a switching element  214 . This is a circuit that applies a voltage between the first electrode  203  and the second electrode  204  so that a voltage waveform becomes trapezoid.  
      The counter voltage generating circuit  211  is connected to the first electrode  203 , and applies an alternating voltage (hereinafter referred to as “AC voltage”) to the first electrode  203  in a rectangular wave mode. The signal voltage generating circuit  212  is connected to the second electrode  204 , and applies an AC voltage to the second electrode  204  in a rectangular wave mode. For this reason, an AC voltage of a difference between the AC voltage generated by the counter voltage generating circuit  211  and the AC voltage generated by the signal voltage generating circuit  212  is applied between the first electrode  203  and the second electrode  204 . The application of this AC voltage generates radical species (radical anion and radical cation) with different polarities which are luminous molecules of the ECL material alternately in the vicinities of the first electrode  203  and the second electrode  204 . When the generated radical anion and radical cation associate with each other to disappear and the excited ECL material is created and deactivated, light is emitted. When such application of the voltage is not successively performed, a non-luminous state is obtained.  
      In this embodiment, the AC voltage is applied between the first electrode  203  and the second electrode  204 , but the counter voltage generating circuit  211  and the signal voltage generating circuit  212  may be constituted so that a direct voltage (hereinafter referred to as “DC voltage”) is applied between the first electrode  203  and the second electrode  204 . The application of the DC voltage allows the first electrode  203  and the second electrode  204  to generate radical anion and radical cation as radical species with different polarities. The generated radical anion and the radical cation associate with each other to disappear, and the excited ECL material is created and deactivated so that the light is emitted.  
      The switching element  214  switches the connection between the second electrode  204  and the signal voltage generating circuit  212  and between the second electrode  204  and earth. That is, when the switching element  214  is switched into a right side of  FIG. 1 , the voltage between the first electrode  203  and the second electrode  204  becomes 0, and when the switching element  214  is switched into a left side of  FIG. 1 , a voltage is applied between the first electrode  203  and the second electrode  204 .  
      The variable resistor  213  applies an AC voltage of the rectangular wave mode generated from the signal voltage generating circuit  212  to the second electrode  204  in a triangular wave mode in which the voltage gradually increases. Further, when a resistance value is variable by using the variable resistor  213 , the gradient of the triangular wave can be arbitrarily changed.  
      That is, as shown in  FIG. 4  for example, when the AC voltage generated from the signal voltage generating circuit  212  is applied to the second electrode  204 , the voltage passes through the variable resistor  213 , so that while the voltage value is gradually increasing for a first period (t 1 ), the voltage reaches a predetermined voltage value at the time when the first period elapses. In this embodiment, a resistor is given to the voltage to be applied so that a trapezoidal waveform is obtained. The trapezoidal waveform is such that the predetermined voltage is maintained for a second period (t 2 ) which starts from the elapse of the first period, and while the voltage is gradually decreasing for a third period (t 3 ) which starts from the elapse of the second period, the voltage value becomes 0 after constant time elapses. When the voltage with such a trapezoidal waveform is applied while its polarity is changed alternately, the AC voltage with the trapezoidal waveform is applied to the second electrode  204 . In the power supply circuit  210  in this embodiment, the voltage is applied between the first electrode  203  and the second electrode  204  repeatedly with a constant cycle by the switching operation of the variable resistor  213  and the switching element  214  so that the voltage waveform for one cycle includes two trapezoidal waveforms with different polarities. Further, when the voltage with the trapezoidal waveform is applied repeatedly without changing the polarity, the DC voltage with the trapezoidal waveform is applied to the second electrode  204 .  
      The voltage is applied in the triangular wave mode by the power supply circuit  210  when the display element L i,j  emits light. As a result, a peak current does not flow, efficient oxidation and reduction cycles are realized, and driving is carried out by a constant voltage so that the light emission with high luminance by the display element L i,j  can be maintained for a long period of time.  
      In this embodiment, the AC voltage is applied between the first electrode  203  and the second electrode  204  by the counter voltage generating circuit  211  and the signal voltage generating circuit  212 , and the variable resistor  213  enables the AC voltage to obtain the trapezoidal waveform. However, a circuit or a circuit element other than the variable resistor  213  can be used as long as the waveform of the voltage becomes trapezoid.  FIG. 2  is a circuit diagram showing an example using a low pass filter  313  (LPF) in order that the waveform of the voltage between the first electrode  203  and the second electrode  204  becomes trapezoid.  
      In the display element L i,j  of this embodiment, the second electrode  204  has a single structure, but the second electrode  204  may be divided into a plurality of portions and the display element L i,j  is used as a segment type display element L i,j .  FIG. 3  is an explanatory diagram showing a configuration of the display element L i,j  and a circuit configuration of the driving unit when the second electrode  204  is divided into a plurality of portions. In this example, as shown in  FIG. 3 , the second electrode is divided into a plurality of electrode portions  204   a  to  204   n , and a plurality of switching elements  214   a  to  214   n  corresponding to them are connected to the signal voltage generating circuit  212  and the electrode portions  204   a  to  204   n.    
      The switching elements  214   a  to  214   n  switch the connection between the connected electrode portions  204   a  to  204   n  as the second electrode and the signal voltage generating circuit  212  and between the electrode portions  204   a  to  204   n  and the earth. When, therefore, the switching elements  214   a  to  214   n  are switched into the right side, the voltage between the first electrode  203  and the electrodes  204   a  to  204   n  becomes 0. When the switching elements  214   a  to  214   n  are switched into the left side shown in  FIG. 3 , the voltage is applied between the first electrode  203  and the electrode portions  204   a  to  204   n.    
      The following explains a waveform of the voltage to be applied between the first electrode  203  and the second electrode  204  of the display element L i,j  by the power supply circuit  210 .  FIG. 4  is an explanatory diagram showing the waveform of the AC voltage to be applied to the display element L i,j  in the display apparatus according to the first embodiment.  FIG. 5  is an explanatory diagram showing the waveform of the DC voltage to be applied to the display element L i,j  in the display apparatus according to the first embodiment. On the other hand,  FIG. 6A  is an explanatory diagram showing the waveform of the AC voltage to be applied to the display element L i,j  in the conventional display apparatus, and  FIG. 6B  is an explanatory diagram showing the waveform of the DC voltage to be applied to the display element L i,j  in the conventional display apparatus. In all  FIGS. 4, 5 ,  6 A and  6 B, the axis of abscissas represents the time, and the axis of ordinates represents the voltage value (V).  
      In contrast to the conventional display apparatus where the AC voltage which has a rectangular waveform with different polarities as shown in  FIG. 6A  is applied to the display element L i,j , in the display apparatus according to the first embodiment, the power supply circuit  210  repeatedly applies the AC voltage which obtains a waveform where trapezoid waves with different polarities appear with each one cycle to the display element L i,j  as shown in  FIG. 4 . In contrast to the conventional display apparatus where the DC voltage which has a rectangular waveform as shown in  FIG. 6B  is applied to the display element L i,j , in the display apparatus according to the first embodiment, the power supply circuit  210  may repeatedly apply the DC voltage which has a trapezoidal waveform with one polarity as shown in  FIG. 5  to the display element L i,j . When the voltage of the rectangular waveform is applied like the conventional display apparatus, a peak of a charging current is observed in the value of the current flowing in the display element L i,j , but it is preferable that the gradient of the trapezoidal waveform in the display apparatus of this embodiment is enough gentle to prevent the peak of the charging current from appearing.  
       FIG. 7  is an explanatory diagram showing comparison of the light emitting state of the display element L i,j  between the display apparatus in the first embodiment and the conventional display apparatus. In  FIG. 7 , the axis of abscissas represents the time, and the axis of ordinates represents the luminance of the display element. In  FIG. 7 , a curve  601  shows the light emitting state (a change in the luminance) of the display element L i,j  in this embodiment, and a curve  602  shows the light emitting state (a change in the luminance) of the display element L i,j  in the conventional display apparatus. As is clear from  FIG. 7 , in this embodiment (curve  601 ), when the voltage of the trapezoidal waveform is repeatedly applied to the display element, the light emission with high luminance by the display element can be maintained for a longer period of time in comparison with the case where the voltage of the rectangular waveform is applied like the conventional display apparatus (curve  602 ).  
      The following explains a configuration of an arrangement of pixels in the display apparatus having the display element L i,j  according to the first embodiment.  FIG. 27  is a plan view showing a part (portion of 2×2) of the arrangement of the pixels in the display apparatus having the display element L i,j  according to the first embodiment. In the display apparatus according to the first embodiment, as shown in  FIG. 27 , pixels X i,j  are respectively arranged inside a matrix two-dimensionally. The matrix is composed of a plurality of signal wirings B 1   j , B 1   j+1  . . . which are laid in a vertical direction (column-wise direction) and a plurality of scanning wirings W 1   i , W 1   i   +1 , . . . which extend in a horizontal direction (row direction) perpendicular to the signal wirings B 1   j , B 1   j+1  . . . (i=1 to n; j=1 to m: n and m are positive integers). Further, power source wirings P 1   j , P 1   j+1 , . . . are laid parallel with the signal wirings B 1   j , B 1   j+1 , . . . .  
      As shown in  FIG. 27 , a first terminal of a writing transistor (TFT) Q 1   i,j  is connected to the signal wiring B 1   j , and a control terminal of the writing transistor Q 1   i,j  is connected to the scanning wiring W 1   i . A second terminal of the writing transistor Q 1   i,j  is connected to a control terminal of a driving transistor (TFT) Q 2   i,j  and one terminal of an auxiliary capacitor C 1   i,j . A first terminal of the driving transistor Q 2   i,j  is connected to the power supply wiring P 1   j , and a second terminal of the driving transistor Q 2   i,j  is connected to a display cell L i,j . The other terminal of the auxiliary capacitor C 1   i,j  is grounded. “The first terminal” means one of an emitter terminal and a collector terminal in a bipolar transistor (BJT). The first terminal means one of a source terminal and a drain terminal in a field-effect transistor (FET) or a static induction transistor (SIT). “The second terminal” means one of an emitter terminal and a collector terminal which does not become the first terminal in BJT or the like, and means one of a source terminal and a drain terminal which does not become the first terminal in FET or SIT. That is, when the first terminal is the emitter terminal, the second terminal is the collector terminal, and when the first terminal is the source terminal, the second terminal is the drain terminal. “The control terminal” means a terminal for controlling an electric current flowing between the first terminal and the second terminal, a Schottky junction terminal, a terminal or a configuration of an insulating gate. For example, the control terminal means the gate terminal or the gate configuration in FET or SIT, and means the base terminal in BJT. Since the first terminal and the second terminal generally have symmetrical configurations in TFT or the like, it is a simply matter of selection as to which is called as the source terminal or the drain terminal or which is called as the emitter terminal or the collector terminal.  
      A first terminal of the writing transistor (TFT) Q 1   i+1,j  is connected to the signal wiring B 1   j , and a control terminal of the writing transistor Q 1   i+1,j  is connected to the scanning wiring W 1   i+1 . A second terminal of a writing transistor Q 1   i+1,j  is connected to a control terminal of a driving transistor (TFT) Q 2   i+1,j  and one terminal of an auxiliary capacitor C 1   i+1,j . A first terminal of the driving transistor Q 2   i+1,j  is connected to the power supply wiring P 1   j , and a second terminal of the driving transistor Q 2   i+1,j  is connected to a display cell L i+1,j . The other terminal of the auxiliary capacitor C 1   i+1,j  is grounded.  
      A first terminal of a writing transistor (TFT) Q 1   i,j+1  is connected to the signal wiring B 1   j+1 , and a control terminal of the writing transistor Q 1   i,j+1  is connected to the scanning wiring W 1   i . A second terminal of the writing transistor Q 1   i,j+1  is connected to a control terminal of a driving transistor (TFT) Q 2   i,j+1  and one terminal of an auxiliary capacitor C 1   i,j+1 . A first terminal of the driving transistor Q 2   i,j+1  is connected to the power supply wiring P 1   j+1 , and a second terminal of the driving transistor Q 2   i,j+1  is connected to a display cell L 1,j+1 . The other terminal of the auxiliary capacitor C 1   i,j+1  is grounded.  
      A first terminal of a writing transistor (TFT) Q 1   i+,j+1  is connected to the signal wiring B 1   j+1 , and a control terminal of the writing transistor Q 1   i+1,j+1  is connected to the scanning wiring W 1   i+1 . A second terminal of the writing transistor Q 1   i+1,j+1  is connected to a control terminal of a driving transistor (TFT) Q 2   i+1,j+1  and one terminal of an auxiliary capacitor C 1   i+1,j+1 . A first terminal of the driving transistor Q 2   i+1,j+1  is connected to the power supply wiring P 1   j+1 , and a second terminal of the driving transistor Q 2   i+1,j+1  is connected to a display cell L i+1,j+1 . The other terminal of the auxiliary capacitor C 1   i+1,j+1  is grounded.  
      The writing transistors Q 1   i,j , Q 1   i+1,j , Q 1   i,j+1  and Q 1   i+1,j+1 , the driving transistors Q 2   i,j , Q 2   i+1,j , Q 2   i,j+1  and Q 2   i+1,j+1  may be TFT which is used for an active matrix substrate used in an LCD or an organic EL.  
      The scanning wirings W 1   i , W 1   i+1 , . . . and the signal wirings B 1   j , B 1   j+1 , . . . are synchronized with each other and the voltage is applied, and display signals from the writing transistors Q 1   i,j , Q 1   i+1,j , Q 1   i,j+1 , Q 1   i+1,j+1  . . . are accumulated in the auxiliary capacities C 1   i,j , C 1   i+1,j , C 1   i,j+1 , C 1   i+1,j+1 , . . . . The driving transistors Q 2   i,j , Q 2   i+1,j , Q 2   i,j+ , Q 2   i+1,j+1  . . . can control the amount of a current to flow in the display cells Li ,j , L i+1,j , L i,j+1  and L i+1,j+1  according to the charge content of the display signals in the auxiliary capacities C 1   i,j, C1   i+1,j , C 1   i,j+1 , C 1   i+1,j+1 , . . . .  
      A second embodiment is explained below.  
      The display apparatus in the first embodiment performs only the luminous display using the electrolyte solution layer of the display element, but the display apparatus in the second embodiment performs the luminous display using a first layer of the display element, and performs reflection display using a second layer of the display element.  
      In the display apparatus in this embodiment, the configuration of the display element L i,j  of the pixel X i,j  is different from that in the first embodiment.  FIG. 8  is a schematically sectional view showing one example of the configuration of the display element L i,j  to be a display cell of the pixel X i,j  in the display apparatus according to the second embodiment, where i=1 to n, j=1 to m, and n and m are positive integers.  
      As shown in  FIG. 8 , each of the pixels X i,j  includes a first layer  806 , a second layer  807 , a first voltage applying unit ( 803 ,  804 , V ECL ), a second voltage applying unit ( 803 ,  804 ,  805 , E 1 , E 2 ), and a switching unit (S 1 , S 2 ). The first layer  806  includes an electrochemical luminescent material (ECL material). The second layer  807  is arranged so as to be opposed to at least a part of the first layer  806  and includes an electrochromic material. The first voltage applying unit applies a voltage to the first layer  806  so as to allow the electrochemical luminescent material to electrochemically emit light. The second voltage applying unit applies a voltage to the electrochromic material (EC material) so as to discolor the electrochromic material. The switching unit selectively operates the first voltage applying unit and the second voltage applying unit. That is, the display cell L i,j  of the pixel X i,j  has a first substrate  801 , and a first electrode-on-first-substrate (electrode on the first ECL side)  803  and a second electrode-on-first-substrate (second electrode on the first ECL side)  804  which are electrically separated from each other are provided onto the first substrate  801 . A second substrate  802  is provided so as to be opposed to and separated from the first substrate  801 , and an electrode-on-second-substrate (electrode on the EC side)  805  is provided onto the second substrate  802 . The first electrode-on-first-substrate  803  is connected to a second terminal of a first driving transistor Q 2   i,j  shown in  FIG. 28 , mentioned later, and the second electrode-on-first-substrate  804  is connected to a second terminal of a second driving transistor Q 4   i,j  shown in  FIG. 28 .  
      Similarly to the electrolyte solution layer of the display apparatus according to the first embodiment, the first layer  806  is a luminescent material. The luminescent material emits light when it is excited by migration and recombination of oxidant (radical cation) and reductant (radical anion) generated by electrochemical oxidation or reduction of the ECL material or another material due to the application of the voltage, and the luminescent material is deactivated. That is, the luminescent material is a material showing electrochemical luminescence (ECL). ECL means that when the ECL material or another material is oxidized near the electrode or an EC film so as to become radical cation or reduced so as to become radical anion by the application of a voltage, and both the radical cation and the radical anion associate with each other to disappear, the excited state of the ECL material is generated and the ECL material emits light at the deactivation process. In such a manner, the luminous display is performed.  
      The first layer  806  includes the ECL material and the electrolyte. Examples of the ECL material are tris(2,2′-bipyrazyl) ruthenium (II) [Ru(bpy)3] 2+  as a chelate metal complex (ruthenium bipyridyl complex), a naphthacene derivative (rubrene expressed by a formula [II], 5,12-diphenyl naphthacene expressed by a formula [IV]), an anthracene derivative (9,10-diphenyl anthracene) expressed by a formula [III], a penthacene derivative (6,10-diphenyl penthacene) and a perifratin derivative (dibenzotetra (methylphenyl) perifratin) expressed by a formula [V] as a polyaromatic compound, a polyparaphenylenevinylene derivative, a polythiophene derivative, a polyparaphenylene derivative, and a polyfluorene derivative as pi-conjugated polymer, coumalin as a heteroaromatic compound, tris(2-phenylpyridine) isodium as an organic metal compound, and a chelate lanthanoid complex.  
                 
                 
                 
 
      Examples of R1 and R2 in the formulas [VII] to [XIV] are an alkyl group, a cycloalkyl group, an alkoxy group, an alkoxyalkyl group, an alkoxyalkoxyalkyl group and an alkoxyalkoxyalkoxyalkyl group in which the number of hydrogens and carbons is up to 24, an aryl group, an aryloxy group and an aralkyl group where the number of carbons is 6 to 18.  
      The electrolyte has a solvent (when the first layer  806  is a liquid layer as the liquid electrolyte), or a gelled polymer which is swelled by the solvent (when the first layer  806  is a solid layer as a solid electrolyte), and a supporting electrolyte which dissolves in the polymer. Examples of the supporting electrolyte are tetrabutylammonium perchlorate, potassium hexafluorophosphate, lithium trifluoromethanesulfonate, lithium perchlorate, tetra-n-butylammonium tetrafluoroborate, tripropylamine, and tetra-n-butylammonium fluoroborate.  
      Examples of the solvent are a single solvent or a mixed solvent composed of acetonitrile, N,N-dimethylform-amide, propylene carbonate, o-dichlorobenzene, 1,2 dimethoxyethane, glycerin, water, ethyl alcohol, propyl alcohol, dimethyl carbonate, ethylene carbonate, γ-butyrollactone, N-methyl-2-pyrrolidone (NMP), 2-methyltetrahydrofuran, toluene, tetrahydrofuran, benzonitrile, cyclohexane, normal hexane, acetone, nitrobenzene, 1,3-dioxolane, furan, benzotrifluoride and the like.  
      Examples of the gelled polymer are a copolymer of polyacrylonitrile (PAN), vinylidene fluoride (VDF) and propylene hexafluoride (HEP), and a polyethylene oxide (PEO).  
      When the first layer  806  is the liquid layer, the supporting electrolyte and the ECL material may be dissolved in the solvent. They may be infused between the first substrate  801  and the second substrate  802 . The first substrate  801  is formed with the first electrode-on-first-substrate  803  and the second electrode-on-first-substrate  804 . The second substrate  802  is constituted so that an electrode-on-second-substrate  805  and a second layer  807  are laminated. When the first layer  806  is the solid layer, a solution of the gelled polymer including the supporting electrolyte and a solvent (the amount of the solvent is larger) may be applied and dried.  
      The second layer  807  includes a coloring material which is discolored due to electrochemical oxidation or reduction caused by the application of a voltage, namely, a material which shows an electrochromic (EC) phenomenon. In the EC phenomenon, the EC material is reduced so as to be colored or is bleached, or is oxidized so as to be bleached or colored. At this time, the electrolyte included in the first layer  806  or electrolyte including ion relating to the EC reaction of the EC material is fundamental to the EC reaction. For example, tungsten oxide (W 1 O 3 ) as the EC material is bleached by the oxidation so as to be transparent, and it is colored by the reduction so as to be blue. Also the ion in the first layer (ECL, electrolyte layer)  806  including the ECL material relates to the EC (oxidation, reduction) reaction of the reflection display depending on the EC materials to be used. When a second layer (EC layer)  807  made of W 1 O 3 , for example, is used as the ECL material, the first layer (electrolyte layer)  806  including the ECL material contains Li +  (lithium salt complex (LiCF 3 SO 3  or the like) as the supporting electrolyte). In this case, the EC reaction like formula (1) occurs. 
 
W 1 O 3 +xe − +xLi +   LixW 1 O 3   (1) 
 
      In the oxidation shown by a left arrow in formula (1), the material is bleached (transparent), and in the reduction shown by a right arrow in formula (1), the material is colored (blue). Such a property of the EC phenomenon is utilized, so that the reflection display is performed. Examples of the EC material to be used for the second layer  807  are manganese oxide (MnO 2 ), cobalt oxyhydroxide (CoOOH), nickel oxyhydroxide (NiOOH), copper oxide (CuO), ruthenium oxide (RuO 2 ), rhodium oxide (Rh 2 O 3 ), iridium oxide (IrO x ), Prussian blue, tungsten oxide (W 1 O 3 ), molybdenum oxide (MoO 3 ) titanic oxide (TiO 2 ), vanadium oxide (V 2 O 5 ), niobium oxide (Nb 2 O 5 ) and silver iodide (AgI) as organic materials.  
      Viologen organic materials as a low molecular organic material can be used as the EC material.  
                 
 
      Another examples of the low-molecular organic material are orthochloranil, a 4-benzoyl pyridium derivative, ruthenium-tris, ruthenium-bis osmium-tris, an osmium-bis type transition metal complex (see formula [XVI]), a polynuclear complex, a ruthenium-cis-diaqua-bipyrisyl complex, phthalocyanine pigment, naphthalocyanine pigment, porphyrin pigment, perylene pigment, anthraquinone pigment, azo pigment, quinophthalone pigment, naphthoquinone pigment, cyanine pigment, merocyanine pigment, a diphthalocyanine complex, 2,4,5,7-tetranitro-9-fluorene, 2,4,7-nitriro-9-fluorenydeline malononitrile and tetra-cyanoquinodimethane. They can be used as the EC material.  
      Further, examples of the EC material are conductive polymer as expressed in formulas [XVII] to [XXIV], such as a polypyrrole derivative, a polythiophene derivative, a polyaniline derivative, a polyazulene derivative, polyisothianaphthene, poly(N-methylisoindole), poly (dithieno[3,4-b: 3 ′,4′-d]thiophene), a polydiallylamine derivative, a polypyrrolopyrol derivative and an Ru complex type conductive polymer. The EC materials are, however, not limited to them.  
                 
 
      Examples of R1 and R2 in the formulas [XVI], [XVIII], [XIX], [XXII] and [XXIII] are an alkyl group, a cycloalkyl group, an alkoxy group, an alkoxyalkyl group, an alkoxyalkoxyalkyl group and an alkoxyalkoxyalkoxyalkyl group in which the number of hydrogens and carbons is up to 24, an aryl group, an aryloxy group and an aralkyl group where the number of carbons is 6 to 18.  
      When an inorganic material is used as the second layer  807 , a film is deposited by vacuum evaporation, sputtering, vapor-phase growth, a solgel method, fine particle sintering or applying and drying a polyacid perioxide solution as a precursor. Further, when the low-molecular organic material is used, it is vacuum-evaporated, or is applied and dried (be soluble). The conductive polymer is applied and dried (be soluble) or is subject to electrolytic polymerization. As a result, a solid layer can be formed.  
      An equivalent circuit in accordance with the configuration of the display element L i,j  to be the display cell of the pixel X i,j  in the display apparatus of the second embodiment shown in  FIG. 8  is explained below. In  FIG. 8 , on an interface between the first electrode-on-first-substrate  803  and the first layer (electrolyte layer)  806 , a parallel circuit composed of an interface resistor R 1 c 1  and an interface capacitor C 1 c 1 , which shows interface impedance of an ion moving process on the interface is provided. Similarly, on an interface between the second electrode-on-first-substrate  804  and the first layer (electrolyte layer)  806 , a parallel circuit composed of an interface resistor R 1 c 2  and an interface capacitor C 1 c 2 , which shows interface impedance of the ion moving process on the interface is provided. The interface impedance of the first electrode-on-first-substrate  803  and the second electrode on the first substrate shown in FIGS.  8  to  11  causes the oxidation and reduction of a host lattice in the first electrode-on-first-substrate  803  and the second electrode-on-first-substrate  804 , namely, exchange of electrons between the host lattice and the first layer (electrolyte layer)  806 , and the movement of the electrons for propagating the oxidation and reduction in the host lattice. Therefore, it is considered that the progress of the reaction of the display cell L i,j  represents respective reaction steps including movement of Li +  across the interface, rearrangement of the host lattices and their propagation, the movement of the electrons in the host lattices, and movement of Li +  on the interface as expressed by formula (1).  
      A resistor R ECL1  to be connected to the parallel circuit composed of the interface resistor R 1 c 1  and the interface capacitor C 1 c 1  shows a resistance component in the first layer (electrolyte layer)  806 , and a resistor R ECL2  to be connected to the parallel circuit composed of the interface resistor R 1 c 2  and also the interface capacitor C 1 c 2  shows a resistance component in the first layer (electrolyte layer)  806 .  
      A parallel circuit composed of an interface resistor R 2 c 1  and an interface capacitor C 2 c 1  connected to the resistor R ECL1  shows interface impedance of the ion moving process on the interface between the first layer (electrolyte layer)  806  and the second layer (EC layer)  807 . Similarly, a parallel circuit composed of an interface resistor R 2 c 2  and an interface capacitor C 2 c 2  connected to the resistor R ECL2  also shows interface impedance of the ion moving process on the interface between the first layer (electrolyte layer)  806  and the second layer (EC layer)  807 .  
      A resistor R EC1  to be connected to the parallel circuit composed of the interface resistor R 2 c 1  and the interface capacitor C 2 c 1  shows a resistance component in the second layer (EC layer)  807 , and a resistor R EC2  to be connected to the parallel circuit composed of the interface resistor R 2 c 2  and the interface capacitor C 2 c 2  also shows a resistance component in the second layer (EC layer)  807 . A resistor R G  which connects the resistor R EC1  and the resistor R EC2  shows a resistance of the electrode-on-second-substrate  805 .  
      In  FIG. 9 , the parallel circuit composed of the interface resistor R 2 c 1  and the interface capacitor C 2 c 1  connected to the resistor R ECL1  and the parallel circuit composed of the interface resistor R 2 c 2  and the interface capacitor C 2 c 2  connected to the R ECL2  shown in  FIG. 8  are omitted, and a resistance component R EC  in the second layer (EC layer)  807  is simply shown. It is considered that the luminous display is performed by causing the ECL reaction in the equivalent circuit of  FIG. 8  and the ECL reaction in the equivalent reaction of  FIG. 9  in a concerted manner. A determination is made which reaction is dominant by components.  
      In the display apparatus according to the second embodiment, similarly to the first embodiment, the first electrode-on-first-substrate  803  and the second electrode-on-first-substrate  804  are connected to an AC power supply circuit V ECL    210  via a switching element S 1 , which composes the first voltage applying unit ( 803 ,  804 , V ECL    210 ) as shown in  FIGS. 8 and 9 .  
      The AC power supply circuit V ECL    210  has the similar configuration to that of the power supply circuit  210  in the first embodiment, and thus is composed of the counter voltage generating circuit  211 , the signal voltage generating circuit  212 , the variable resistor  213  and the switching element  214 . It is a power supply circuit that applies an AC voltage between the first electrode-on-first-substrate  803  and the second electrode-on-first-substrate  804  so that the voltage waveform becomes trapezoid as shown in  FIG. 4 .  
      Specifically, the counter voltage generating circuit  211  is connected to the first electrode-on-first-substrate  803 , and the signal voltage generating circuit  212  is connected to the second electrode-on-first-substrate  804  via the variable resistor  213  and the switching element  214 . Similarly to the first embodiment, when the AC voltage generated from the signal voltage generating circuit  212  is applied to the second electrode-on-first-substrate  804 , the AC voltage passes through the variable resistor  213 , so that while the voltage value is being gradually increased for a first period, the voltage is allowed to reach a predetermined voltage value at the time when the first period elapses. The predetermined voltage is maintained for a second period starting from the elapse of the first period. While the voltage is being gradually reduced for a third period starting from the elapse of the second period, the voltage is applied so that the voltage obtains a trapezoidal waveform where the value becomes 0 after elapse of constant period of time. Such application of the voltage is repeated so that the trapezoidal waveform where the polarity differs alternately is obtained. In such a manner, the AC voltage of trapezoidal waveform is applied.  
      In the AC power supply circuit V ECL    210 , the AC voltage is applied between the first electrode-on-first-substrate  803  and the second electrode-on-first-substrate  804  by the switching operation of the variable resistor  213  and the switching element  214  repeatedly per constant cycle so that the voltage waveform for one cycle becomes trapezoid as shown in  FIG. 4 .  
      In the AC power supply circuit V ECL    210  according to this embodiment, the counter voltage generating circuit  211  is connected to the first electrode-on-first-substrate  803 , and the signal voltage generating circuit  212  is connected to the second electrode-on-first-substrate  804  via the variable resistor  213  and the switching element  214 . On the contrary, however, the counter voltage generating circuit  211  may be connected to the second electrode-on-first-substrate  804 , and the signal voltage generating circuit  212  may be connected to the first electrode-on-first-substrate  803  via the variable resistor  213  and the switching element  214 .  
      In this embodiment, the variable resistor  213  is used in the AC power supply circuit V ECL    210  so that the voltage waveform becomes trapezoid. Instead of the variable resistor  213 , another circuit such as the low pass filter  313  shown in  FIG. 2  may be used so that the voltage waveform becomes trapezoid.  
      The display element L i,j  shown in  FIGS. 8 and 9  has the configuration when the inside state of the pixel X i,j  is observed from the first substrate  801  side. The first substrate  801  is made of a transparent material, and the first electrode-on-first-substrate  803  and the second electrode-on-first-substrate  804  are preferably made of an approximately transparent material.  
      On the contrary, the display element L i,j  shown in  FIG. 10  has the configuration when the inside state of the pixel X i,j  is observed from the second substrate  802  side. The second substrate  802  and the electrode-on-second-substrate  805  are made of a transparent material, and the first electrode-on-first-substrate  803  and the second electrode-on-first-substrate  804  or the first substrate  801  function as a reflection layer, or a reflection layer is separately provided. Since the first substrate  801  is normally a portion to be an observation surface of the display apparatus, the first substrate  801  is formed by an optically-transparent material. As such an optically-transparent material, materials where absorption is less in the visible light region, such as inorganic material such as glass and organic material such as optically-transparent resin are preferable. Concrete examples are polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyether sulfon (PES), and polycarbonate (PC). The second substrate  802  does not require the optically-transparent property, but it is generally made of the similar material to the first substrate  801 . The other part of the configuration other than such a material is similar to the display element L i,j  shown in  FIG. 9 .  
      As shown in  FIG. 11 , the DC power supply circuit  210  composed of the counter voltage generating circuit  211  and the signal voltage generating circuit  212  may be connected so that a DC voltage is applied between the first electrode-on-first-substrate  803  and the second electrode-on-first-substrate  804 . The DC power supply circuit  210  has the similar configuration to that of the power supply circuit  210  in the first embodiment. The circuit  210  is composed of DC power supply E ECL  including the counter voltage generating circuit  211  and the signal voltage generating circuit  212 , the variable resistor  213  and the switching element  214 . It applies a DC voltage between the first electrode-on-first-substrate  803  and the second electrode-on-first-substrate  804  so that the voltage waveform becomes trapezoid as shown in  FIG. 5 .  
      More specifically, the counter voltage generating circuit  211  is connected to the first electrode-on-first-substrate  803 , and the signal voltage generating circuit  212  is connected to the second electrode-on-first-substrate  804  via the variable resistor  213  and the switching element  214 . Similarly to the first embodiment, when the DC voltage generated from the signal voltage generating circuit  212  is applied to the second electrode-on-first-substrate  804 , the voltage passes through the variable resistor  213 . As a result, while the voltage value is being gradually increased for the first period, the voltage is allowed to reach a predetermined voltage value at the time when the first period elapses. The predetermined voltage is maintained for the second period starting from the elapse of the first period, and while the voltage value is being gradually reduced for the third period starting from the elapse of the second period, the voltage is applied so as to have a trapezoidal waveform where the value becomes 0 after elapse of constant period of time. Such application is repeated without changing polarity, so that the DC voltage with a trapezoid waveform is applied.  
      In the DC power supply circuit  210 , the DC voltage is applied between the first electrode-on-first-substrate  803  and the second electrode-on-first-substrate  804  by the switching operation of the variable resistor  213  and the switching element  214  repeatedly per constant cycle so that the voltage waveform for one cycle becomes trapezoid as shown in  FIG. 5 .  
      In the display apparatus according to the second embodiment, the display element shown in  FIGS. 8 and 9  is used so that a user can select the luminous display or the reflection display. That is, the user can selectively instruct any one display according to the usage environment. The AC power supply circuit V ECL    210  (or the DC power supply circuit  210 ) and the DC power supplies E 1  and E 2  with different polarities are switched according to the switch instruction information. As a result, a predetermined voltage is applied to the first electrode-on-first-substrate  803 , the second electrode-on-first-substrate  804  and the electrode-on-second-substrate  805 , so that the inside state of the pixel X i,j  is displayed by the luminous display or the reflection display.  
      In the display apparatus according to the second embodiment, the AC power supply circuit V ECL    210  and the DC power supply circuit  210  repeat the application of the voltage with trapezoidal waveform to the display element. As a result, the light emission with high luminance by the display element can be maintained for a longer period of time in comparison with the case where the voltage with rectangular waveform is applied like the conventional display apparatuses.  
      A third embodiment is explained below.  
      In the display apparatus of the second embodiment, the two electrodes on the first substrate side are provided onto the first substrate  801 , but in the display apparatus according to the third embodiment, a single electrode on the first substrate side is provided onto the first substrate  801  as shown in  FIG. 12 .  
       FIG. 12  is a sectional view schematically showing a configuration of the display element L i,j  to be the display cell in the display apparatus according to the third embodiment. Only a part of the display apparatus in the third embodiment which is different from the second embodiment is explained, and the like parts are designated by like reference numerals, and their explanation is not repeated.  
      The reflection/luminous display realized by the display element L i,j  in the first embodiment can be switched by a difference in an effective voltage (electric potential) and a reaction speed necessary for the ECL reaction and the EC reaction. On the contrary, in the display apparatus according to the third embodiment, only an electrode-on-first substrate  823  is provided onto the first substrate  801  as shown in  FIG. 12 .  
      In the display apparatus according to the third embodiment, the electrode-on-first-substrate (electrode on the ECL side)  823  and the electrode-on-second-substrate (electrode on the EC side)  805  are connected to the AC power supply circuit V 3  via the switching element S 3  as shown in  FIG. 12 . They compose the first voltage applying unit ( 823 ,  805 , V 3 ). The electrode-on-first-substrate  823  and the electrode-on-second-substrate  805  are connected to the DC power supplies E 1  and E 2  with different polarities via the switching element S 2 . They compose the second voltage applying unit ( 823 ,  805 , E 1 , E 2 ).  
      The switching elements S 3  and S 2  selectively operate the first voltage applying unit ( 823 ,  805 , V 3 ,  210 ) and the second voltage applying unit ( 823 ,  805 , E 1 , E 2 ).  
      In the configuration shown in  FIG. 12 , when the switching element S 2  is opened, the switching element S 3  is closed, and an AC voltage is applied between the electrode-on-first-substrate  823  and the electrode-on-second-substrate  805  at a frequency which the EC reaction cannot follow. In the luminous display, light emission can be observed in the first layer  806 .  
      In the reflection display, the switching element S 2  is closed, the switching element S 3  is opened, and the DC power supplies E 1  and E 2  with different polarities is connected between the electrode-on-first-substrate  823  and the electrode-on-second-substrate  805 . A voltage (electric potential) for causing the EC reaction is applied therebetween, and coloring and bleaching are observed in the second layer  807 . When the polarities of the applied voltages from the DC power supplies E 1  and E 2  are changed, the color of the second layer  807  becomes transparent, or the transparent second layer  807  is colored. As a result, a background color or the coloring is observed from the first substrate  801  side. At the time of driving the reflection display, an electric double layer is formed on the interface between the ECL and electrolyte layer and EC layer in the second layer  807 /first layer  806 . As a result, ions come in and out of the second layer  807  via the first layer  806 , and also the ECL material occasionally oxidized and reduced (possibly, malfunction in the luminous display). However, a voltage (electric potential) and an electric current which are suitable for the EC reaction are controlled by dropping the effective voltage (electric potential) of the second layer  807  or the like, so that satisfactory reflection display can be performed.  
      In this embodiment, similarly to the first embodiment, when the AC voltage generated from the signal voltage generating circuit  212  is applied to the electrode-on-first-substrate  823 , the voltage passes through the variable resistor  213 . As a result, while the voltage value is gradually increased for the first period (t 1 ) shown in  FIG. 4 , the voltage is allowed to obtain a predetermined voltage value at the time when the first period elapses. The predetermined voltage is maintained for the second period (t 2 ) starting from the elapse of the first period, and while the voltage value is being gradually reduced for the third period (t 3 ) starting from the elapse of the second period, the voltage is applied so that the voltage has a trapezoidal waveform where the value becomes 0 after the elapse of a constant period of time. Such application is repeated so that the voltage has the trapezoidal waveform where polarities differ alternately. In such a manner, the AC voltage of the trapezoid waveform is applied.  
      In the AC power supply circuit V 3   210 , the AC voltage is applied between the electrode-on-first-substrate  823  and the electrode-on-second-substrate  805  by the switching operation of the variable resistor  213  and the switching element  214  repeatedly per constant cycle so that the voltage waveform for one cycle becomes trapezoid as shown in  FIG. 4 .  
      In the AC power supply circuit V 3   210  of this embodiment, the counter voltage generating circuit  211  is connected to the electrode-on-second-substrate  805 , and the signal voltage generating circuit  212  is connected to the electrode-on-first substrate  823  via the variable resistor  213  and the switching element  214 . On the contrary, the counter voltage generating circuit  211  may be connected to the electrode-on-first substrate  823 , and the signal voltage generating circuit  212  may be connected to the electrode-on-second-substrate  805  via the variable resistor  213  and the switching element  214 .  
      In this embodiment, the variable resistor  213  is used in the AC power supply circuit V 3   210  so that the voltage waveform becomes trapezoid. Instead of the variable resistor  213 , however, another circuit such as the low pass filter  313  shown in  FIG. 2  may be used so that the voltage waveform becomes trapezoid.  
      Further, in this embodiment, the AC power supply circuit V 3   210  applies the AC voltage between the electrode-on-first substrate  823  and the electrode-on-second-substrate  805 . However, the counter voltage generating circuit  211  and the signal voltage generating circuit  212  may be constituted so that a DC voltage with trapezoidal waveform shown in  FIG. 5  is applied between the electrode-on-first substrate  823  and the electrode-on-second-substrate  805 .  
      According to the display apparatus according to the third embodiment, the reflection and luminous display can be realized by the simpler configuration in comparison with the second embodiment.  
      In the display apparatus according to the third embodiment, the AC power supply circuit V 3   210  repeatedly applies the voltage with trapezoidal waveform to the display element. As a result, the light emission with high luminance by the display element can be maintained for a longer period of time in comparison with the case where the voltage with rectangular waveform is applied like the conventional display apparatuses.  
      A fourth embodiment is explained below.  
      The display apparatus according to the fourth embodiment in the configuration of the display element further includes an intermediate electrode and an electrolyte layer. In the display apparatus according to this embodiment, the configuration of the display element L i,j  in the pixel X i,j  is different from the configuration in the first embodiment.  
       FIGS. 13 and 14  are sectional views schematically showing the display element L i,j  to be the pixel X i,j  in the display apparatus according to the fourth embodiment. Only portions of the display apparatus according to the fourth embodiment which are different from the second embodiment are explains, and like portions are designated by like reference numerals, and the explanation thereof is not repeated.  
      As shown in  FIGS. 13 and 14 , in the display element L i,j  of the display apparatus according to the fourth embodiment, transparent intermediate electrode  811  and electrolyte layer  812  are provided between the second layer  807  and the first layer  806 . The intermediate electrode  811  is normally made of an optically-transparent material so that display can be observed. Examples of the optically-transparent material are oxide of transition metal such as (compound) oxide of titanium (Ti), zirconium (Zr), hafnium (Hf), strontium (Sr), zinc (Zn), tin (Sn), indium (In), yttrium (Y), lanthanum (La), vanadium (V), niobium (Nb), tantalum (Ta), chromium (Cr), molybdenum (Mo) and tungsten (W) as metal oxide semiconductor, perovskite such as SrTiO 3 , CaTiO 3 , BlaTiO 3 , MgTiO 3  and SrNb 2 O 6 , compound oxide and oxide mixture of them, and gallium nitride (GaN). Examples of the transparent electrode to be frequently used are an oxide indium (In 2 O 3 ) film (ITO) where tin (Sn) is doped, an oxide zinc (ZnO) film (IZO) where indium (In) is doped, an oxide zinc film (GZO) where gallium (Ga) is doped, and an oxide zinc film (FTO) where oxide tin (SnO 2 ) and fluorine for acid resistance are doped.  
      The material of the electrolyte layer  812  includes a solvent (when the first layer  806  is a liquid layer as the liquid electrolyte) or a gelled polymer which is swelled by this solvent (when the first layer  806  is a solid layer as a solid electrolyte) and a supporting electrolyte which is dissolved with the solvent or the polymer. Examples of the supporting electrolyte are tetrabutylammonium perchlorate, potassium hexafluorophosphate, lithium trifluoromethanesulfonate, lithium perchlorate, tetra-n-butylammonium tetrafluoroborate, tripropyl amine, and tetra-n-butylammonium fluoroborate.  
      Examples of the solvent are single solvent or mixed solvent composed of acetonitrile, N,N-dimethylformamide, propylene carbonate, o-dichlorobenzene, 1,2dimethoxyethane, glycerin, water, ethyl alcohol, propyl alcohol, dimethyl carbonate, ethylene carbonate, γ-butylolactone, N-methyl-2-pyrrolidone (NMP), 2-methyltetrahydrofuran, toluene, tetrahydrofuran, benzonitrile, cyclohexane, n-hexane, acetone, nitrobenzene, 1.3-dioxolan, furan, benzotrifuloride and the like.  
      Examples of the gelled polymer are a copolymer of polyacrylonitrile (PAN), vinylidene fluoride (VDF) and vinylidene hexafluoride (HFP), and polyethylene oxide (PEO).  
      The luminous display is preformed by applying an AC voltage between the first electrode-on-first-substrate (first electrode on the ECL side)  803  and the second electrode-on-first-substrate (second electrode on the ECL side)  804 .  
      In the display apparatus according to the fourth embodiment, the first electrode-on-first-substrate  803  and the second electrode on the first electrode side  804  are connected to the AC power supply circuit V ECL    210  via the switching element S 4  as shown in  FIG. 13 . They compose the first voltage applying unit ( 803 ,  803 , V ECL    210 ). The switching elements S 4  and S 2  selectively operate the first voltage applying unit ( 803 ,  804 , V ECL    210 ) and the second voltage applying unit ( 811 ,  805 , E 1 , E 2 ).  
      In the configuration shown in  FIG. 13 , in the luminous display, the switching element S 2  is opened, the intermediate electrode  811  and the electrode-on-second-substrate (electrode on the EC side)  805  are disconnected from the DC power supplies E 1  and E 2 . Further, the switching element S 4  is closed, and the first electrode-on-first-substrate  803  and the second electrode-on-first-substrate  804  are connected to the AC power supply circuit V ECL    210 . An AC voltage is, therefore, generated between the first electrode-on-first-substrate  803  and the second electrode-on-first-substrate  804  (via the intermediate electrode  811 ). The first layer  806  including the luminescent material emits light due to the voltage, and luminous color is observed. If a color filter is provided onto the first substrate  801  of the pixel X i,j , the filter color is observed from the first substrate  801  side. When the application of the voltage from the AC power supply circuit V ECL    210  is stopped, the first layer  806  does not emit light, and a background color of the pixel X i,j , for example, black is displayed.  
      The AC power supply circuit V ECL    210  has the configuration similar to that of the power supply circuit  210  in the first embodiment. The circuit V ECL    210  is composed of the counter voltage generating circuit  211 , the signal voltage generating circuit  212 , the variable resistor  213  and the switching element  214 . It is a power supply circuit that applies an AC voltage between the first electrode-on-first-substrate  803  and the second electrode-on-first-substrate  804  so that the voltage has a trapezoidal waveform shown in  FIG. 4 .  
      More specifically, the counter voltage generating circuit  211  is connected to the first electrode-on-first-substrate  803 , and the signal voltage generating circuit  212  is connected to the second electrode-on-first-substrate  804  via the variable resistor  213  and the switching element  214 . Similarly to the first embodiment, when the AC voltage generated from the signal voltage generating circuit  212  is applied to the second electrode-on-first-substrate  804 , the voltage passes through the variable resistor  213 . As a result, while the voltage value is being gradually increased for the first period (t 1 ) shown in  FIG. 4 , the voltage is allowed to obtain a predetermined voltage value at the time when the first period elapses. The predetermined voltage is maintained for the second period (t 2 ) starting from the elapse of the first period, and while the voltage value is being gradually reduced for the third period (t 3 ) starting from the elapse of the second period, the voltage is applied so as to have a trapezoidal waveform where the value becomes 0 after the constant period of time elapses. Such application is repeated so that the voltage has the trapezoidal waveform where polarities differ alternately. As a result, the AC voltage with trapezoid wave is applied.  
      In the AC power supply circuit V ECL    210 , the AC voltage is applied between the first electrode-on-first-substrate  803  and the second electrode-on-first-substrate  804  repeatedly per constant cycle by the switching operation of the variable resistor  213  and the switching element  214  so that the voltage waveform for one cycle becomes trapezoid as shown in  FIG. 4 .  
      In the AC power supply circuit V ECL    210  of this embodiment, the counter voltage generating circuit  211  is connected to the first electrode-on-first-substrate  803 , and the signal voltage generating circuit  212  is connected to the second electrode-on-first-substrate  804  via the variable resistor  213  and the switching element  214 . On the contrary, however, the counter voltage generating circuit  211  may be connected to the second electrode-on-first-substrate  804 , and the signal voltage generating circuit  212  may be connected to the first electrode-on-first-substrate  803  via the variable resistor  213  and the switching element  214 .  
      In this embodiment, the variable resistor  213  is used in the AC power supply circuit  210  so that the voltage waveform becomes trapezoid. Instead of the variable resistor  213 , however, another circuit such as the low pass filter  313  shown in  FIG. 2  may be used, so that the voltage waveform becomes trapezoid.  
      In this embodiment, the AC power supply circuit V ECL    210  applies the AC voltage between the first electrode-on-first-substrate  803  and the second electrode-on-first-substrate  804 . As shown in  FIG. 14 , however, the DC power supply circuit  210  may be composed of the counter voltage generating circuit  211  and the signal voltage generating circuit  212  so as to apply the DC voltage with trapezoidal waveform shown in  FIG. 5  between the first electrode-on-first-substrate  803  and the second electrode-on-first-substrate  804 . The DC power supply circuit  210  has the similar configuration to that of the power supply circuit  210  in the first embodiment, and is composed of the DC power supply E ECL  including the counter voltage generating circuit  211  and the signal voltage generating circuit  212 , the variable resistor  213 , and the switching element  214 . it is a power supply circuit that applies the DC voltage between the first electrode-on-first-substrate  803  and the second electrode on the first electrode side  804  so that the voltage waveform becomes trapezoid.  
      More specifically, the counter voltage generating circuit  211  is connected to the first electrode-on-first-substrate  803 , and the signal voltage generating circuit  212  is connected to the second electrode-on-first-substrate  804  via the variable resistor  213  and the switching element  214 . Similarly to the first embodiment, when the DC voltage generated from the signal voltage generating circuit  212  is applied to the second electrode-on-first-substrate  804 , the voltage passes through the variable resistor  213 . While the voltage value is being gradually increased for the first period, the voltage is allowed to obtain a predetermined voltage value at the time when the first period elapses. The predetermined voltage is maintained for the second period starting from the elapse of the first period, and while the voltage value is being gradually decreased for the third period starting from the elapse of the second period, the voltage is applied so as to obtain a trapezoidal waveform where the value becomes 0 after a constant period of time elapses. Such application is repeated without changing polarity, so that the DC voltage of trapezoid wave is applied.  
      In the DC power supply circuit  210 , the DC voltage is applied between the first electrode-on-first-substrate  803  and the second electrode-on-first-substrate  804  by the switching operation of the variable resistor  213  and the switching element  214  repeatedly per constant cycle as shown in  FIG. 5  so that the voltage waveform for one cycle becomes trapezoid.  
      In the DC power supply circuit  210  of this embodiment, the counter voltage generating circuit  211  is connected to the first electrode-on-first-substrate  803 , and the signal voltage generating circuit  212  is connected to the second electrode-on-first-substrate  804  via the variable resistor  213  and the switching element  214 . On the contrary, however, the counter voltage generating circuit  211  may be connected to the second electrode-on-first-substrate  804 , and the signal voltage generating circuit  212  may be connected to the first electrode-on-first-substrate  803  via the variable resistor  213  and the switching element  214 .  
      In this embodiment, the variable resistor  213  is used in the DC power supply circuit  210 , so that the voltage waveform becomes trapezoid. Instead of the variable resistor  213 , however, another circuit such as the low pass filter  313  shown in  FIG. 2  may be used so that the voltage waveform may be trapezoid.  
      In the luminous display of  FIG. 14 , the switching element S 12  is opened, and the intermediate electrode  811  and the electrode-on-second-substrate  805  are disconnected from the DC power supplies E 1  and E 2 . Further, the switching element S 4  is closed, and the first electrode-on-first-substrate  803  and the second electrode-on-first-substrate  804  are connected to the DC power supply circuit  210 . A DC voltage is, therefore, generated between the first electrode-on-first-substrate  803  and the second electrode-on-first-substrate  804  (via the intermediate electrode  811 ). The first layer  806  including the luminescent material emits lie due to the voltage, and luminous color is observed. Similarly to  FIG. 13 , if a color filter is provided onto the first substrate  801  of the pixel X i,j , the filter color is observed from the first substrate  801  side. When the application of the voltage from the DC power supply circuit  210  is stopped, the first layer  806  does not emit light, and thus the background color of the pixel X i,j , for example, black is displayed.  
      In the reflection display, the switching element S 2  is closed, and the intermediate electrode  811  and the electrode-on-second-substrate  805  are connected to any of the DC power supplies E 1  and E 2  with different polarities, respectively. Therefore, the DC voltage is generated between the intermediate electrode  811  and the electrode-on-second-substrate  805 , and the second layer  807  including the material showing the EC phenomenon is colored or becomes transparent. As a result, the second substrate  802  is observed as a background color via the colored second layer  807  or the transparent second layer  807  from the outside of the first substrate  801 . When the polarities of the applied voltages from the DC power supplies E 1  and E 2  are changed, the colored second layer  807  becomes transparent or the transparent second layer  807  is colored. As a result, the background color or the color of the second layer  807  is observed from the first substrate  801  side.  
      According to the display apparatus in the fourth embodiment, the reflection display unit and the luminous display unit become independent systems, and thus malfunction hardly occurs.  
      In the display apparatus according to the fourth embodiment, when the AC power supply circuit V ECL    210  or the DC power supply circuit  210  repeat the application of the voltage of trapezoidal waveform to the display element, the light emission with high luminance can be maintained for a longer period of time in comparison with the case where a voltage with rectangular waveform is applied like conventional display apparatuses.  
      A fifth embodiment is explained below.  
      In the display apparatus according to the fourth embodiment, the two electrodes on the first substrate side are formed on the first substrates  801 , but in the display apparatus according to the fifth embodiment, a single electrode on the first substrate side is provided onto the first substrate  801 .  
       FIGS. 15 and 16  are sectional views schematically showing configurations of the display element L i,j  to be the display cell in the display apparatus according to the fifth embodiment. As to the display apparatus according to the fifth embodiment, only portions different from the fourth embodiment are explained, and like portions are designated by like reference numerals and the explanation thereof is not repeated.  
      In the display element L i,j  according to this embodiment, as shown in  FIGS. 15 and 16 , the intermediate electrode  811  and the electrolyte layer  812  are provided between the second layer  807  and the first layer  806 . This point is similar to the display element L i,j  of the pixel X i,j  in the display apparatus according to the fourth embodiment. However, only the electrode on the first substrate side (electrode on the ECL side)  803  is provided to the first substrate  801  similarly to the display apparatus according to the third embodiment. This point is different from the display element L i,j  of the pixel X i,j  in the display apparatus according to the fourth embodiment.  
      The intermediate electrode  811  is normally made of an optically-transparent material so that the display can be observed. Examples of the optically-transparent material are oxide of transition metal such as (compound) oxide of titanium (Ti), zirconium (Zr), hafnium (Hf), strontium (Sr), zinc (Zn), tin (Sn), indium (In), yttrium (Y), lanthanum (La), vanadium (V), niobium (Nb), tantalum (Ta), chromium (Cr), molybdenum (Mo) and tungsten (W) as metal oxide semiconductor, perovskite such as SrTiO 3 , CaTiO 3 , BlaTiO 3 , MgTiO 3  and SrNb 2 O 6 , compound oxide of them and oxide mixture, and gallium nitride (GaN). Examples of the transparent electrode to be frequently used are an oxide indium (In 2 O 3 ) film (ITO) where tin (Sn) is doped, an oxide zinc (ZnO) film (IZN) where indium (In) is doped, an oxide zinc film (GZO) where gallium (Ga) is doped, and an oxide zinc film (FTO) where oxide tin (SnO 2 ) and fluorine for acid resistance are doped. The material of the electrolyte layer  812  includes a solvent (when the first layer  806  is a liquid layer as the liquid electrolyte) or a gelled polymer which is swelled by this solvent (when the first layer  806  is a solid layer as a solid electrolyte) and a supporting electrolyte which is dissolved with the solvent or the polymer. Examples of the supporting electrolyte are tetrabutylammonium perchlorate, potassium hexafluorophosphate, lithium trifluoromethanesulfonate, lithium perchlorate, tetra-n-butylammonium tetrafluoroborate, tripropyl amine, and tetra-n-butylammonium fluoroborate.  
      Examples of the solvent are single solvent or mixed solvent composed of acetonitrile, N,N-dimethylformamide, propylene carbonate, o-dichlorobenzene, 1,2dimethoxyethane, glycerin, water, ethyl alcohol, propyl alcohol, dimethyl carbonate, ethylene carbonate, γ-butylolactone, N-methyl-2-pyrrolidone (NMP), 2-methyltetrahydrofuran, toluene, tetrahydrofuran, benzonitrile, cyclohexane, n-hexane, acetone, nitrobenzene, 1.3-dioxolan, furan, benzotrifuloride and the like.  
      Examples of the gelled polymer are a copolymer of polyacrylonitrile (PAN), vinylidene fluoride (VDF) and vinylidene hexafluoride (HFP), and polyethylene oxide (PEO).  
      In the pixel X i,j  of the display apparatus according to the fifth embodiment, as shown in  FIG. 15 , the electrode-on-first substrate  823  and the intermediate electrode  811  are connected to the DC power supply circuit  210  via the switching element S 5   d . The DC power supply circuit  210  is composed of a DC power supply E ECL    1  and a DC power supply E ECL    2  including the counter voltage generating circuit  211  and the signal voltage generating circuit  212 , variable resistor  213  and the switching element  214 . The DC power supply circuit  210  is a circuit that applies a DC voltage between the electrode-on-first substrate  823  and the intermediate electrode  811  so that the voltage waveform becomes trapezoid. The DC power supplies E ECL    1  and E ECL    2  have different polarities. The DC power supply circuit  210 , the electrode-on-first substrate  823  and the intermediate electrode  811  compose the first voltage applying unit ( 823 ,  811 ,  210 ).  
      The switching elements S 5   d  and S 2  selectively operate the first voltage applying unit ( 823 ,  811 ,  210 ) and the second voltage applying unit ( 811 ,  805 , E 1 , E 2 ).  
      The counter voltage generating circuit  211  is connected to the electrode-on-first substrate  823 , and the signal voltage generating circuit  212  is connected to the intermediate electrode  811  via the variable resistor  213  and the switching element  214 .  
      Similarly to the first embodiment, when the DC voltage generated from the signal voltage generating circuit  212  is applied to the intermediate electrode  811 , the voltage passes through the variable resistor  213 . While the voltage value is being gradually increased for the first period, the voltage is allowed to obtain a predetermined voltage value at the time when the first period elapses. The predetermined voltage is maintained for the second period starting from the elapse of the first period, and while the voltage value is being gradually decreased for the third period starting from the elapse of the second period, the voltage is applied so as to obtain a trapezoidal waveform where the value becomes 0 after a constant period of time elapses. Such application is repeated without changing polarity, so that the DC voltage of trapezoid wave is applied.  
      In the configuration shown in  FIG. 15 , the switching element S 2  is opened, and the intermediate electrode  811  and the electrode-on-second-substrate (electrode on the EC side)  805  are disconnected from the DC power supplies E 1  and E 2 . Further, the switching element S 5   d  is closed with one of the polarities, and the electrode on the first substrate side  803  and the intermediate electrode  811  are connected to any of the DC power supplies E ECL    1  and E ECL    2  having different polarities, respectively. A DC voltage is, therefore, generated between the electrode-on-first substrate  823  and the intermediate electrode  811 , and the first layer  806  including the luminescent material emits light due to this voltage so that the luminescence color is observed. If a color filter is provided onto the first substrate  801  of the pixel X i,j , the filter color is observed from the first substrate  801  side. When the application of the voltage from the DC power supply circuit  210  is stopped, the first layer  806  does not emit light, and the background color of the pixel X i,j , for example, black is displayed.  
      In the DC power supply circuit  210 , the DC voltage is applied between the electrode-on-first substrate  823  and the intermediate electrode  811  by the switching operation of the variable resistor  213  and the switching element  214  repeatedly per constant cycle as shown in  FIG. 5  so that the voltage waveform for one cycle becomes trapezoid.  
      In the DC power supply circuit  210  of this embodiment, the counter voltage generating circuit  211  is connected to the electrode-on-first substrate  823 , and the signal voltage generating circuit  212  is connected to the intermediate electrode  811  via the variable resistor  213  and the switching element  214 . On the contrary, however, the counter voltage generating circuit  211  may be connected to the intermediate electrode  811 , and the signal voltage generating circuit  212  may be connected to the electrode on the first substrate side  803  via the variable resistor  213  and the switching element  214 .  
      In this embodiment, the variable resistor  213  is used in the DC power supply circuit  210 , so that the voltage waveform becomes trapezoid. Instead of the variable resistor  213 , however, another circuit such as the low pass filter  313  shown in  FIG. 2  may be used so that the voltage waveform becomes trapezoid.  
      Meanwhile, in  FIG. 16 , the electrode-on-first substrate  823  and the intermediate electrode  811  are connected to the AC power supply circuit V ECL    210  via the switching element S 5   a , which compose the first voltage applying unit ( 823 ,  811 , V ECL    210 ).  
      The AC power supply circuit V ECL    210  has the similar configuration to that of the power supply circuit  210  in the first embodiment, and is composed of the counter voltage generating circuit  211 , the signal voltage generating circuit  212 , the variable resistor  213 , and the switching element  214 . It is a power supply circuit that applies the AC voltage between the electrode on the first substrate side  803  and the intermediate electrode  811  so that the voltage waveform becomes trapezoid.  
      More specifically, the counter voltage generating circuit  211  is connected to the intermediate electrode  811 , and the signal voltage generating circuit  212  is connected to the electrode-on-first substrate  823  via the variable resistor  213  and the switching element  214 . Similarly to the first embodiment, when the AC voltage generated from the signal voltage generating circuit  212  is applied to the electrode-on-first substrate  823 , the voltage passes through the variable resistor  213 . As a result, while the voltage value is being gradually increased for the first period, the voltage is allowed to obtain a predetermined voltage value at the time when the first period elapses. The predetermined voltage is maintained for the second period starting from the elapse of the first period, and while the voltage value is being gradually decreased for the third period starting from the elapse of the second period, the voltage is applied so as to obtain a trapezoidal waveform where the value becomes 0 after a constant period of time elapses. Such application is repeated so that the voltage has trapezoidal waveform where polarities differ alternately. In such a manner, the AC voltage of trapezoid wave is applied.  
      In the AC power supply circuit V ECL    210 , the AC voltage is applied between the electrode-on-first substrate  823  and the intermediate electrode  811  by the switching operation of the variable resistor  213  and the switching element  214  repeatedly per constant cycle as shown in  FIG. 4  so that the voltage waveform for one cycle becomes trapezoid.  
      In the AC power supply circuit V ECL    210  of this embodiment, the counter voltage generating circuit  211  is connected to the intermediate electrode  811 , and the signal voltage generating circuit  212  is connected to the electrode-on-first substrate  823  via the variable resistor  213  and the switching element  214 . On the contrary, however, the counter voltage generating circuit  211  may be connected to the electrode-on-first substrate  823 , and the signal voltage generating circuit  212  may be connected to the intermediate electrode  811  via the variable resistor  213  and the switching element  214 .  
      According to the display apparatus in the fifth embodiment, the reflection display unit and the luminous display unit become independent systems, and thus the reflection display and the luminous display can be realized by more simple configuration in comparison with the fourth embodiment.  
      In the display apparatus according to the fifth embodiment, when the AC power supply circuit V ECL    210  repeats the application of the voltage of trapezoidal waveform to the display element, the light emission with high luminance by the display element can be maintained for a longer period of time in comparison with the case where a voltage with rectangular waveform is applied like conventional display apparatuses.  
      A sixth embodiment is explained below.  
      In the display apparatus according to the sixth embodiment, an electrolyte layer and a porous electrode are further provided to the display element. In the display apparatus according to this embodiment, the configuration of the display element L i,j  of the pixel X i,j  is different from that in the first embodiment. As to the display apparatus according to the sixth embodiment, only different point from the first embodiment is explained, and like portions are designated by like reference numerals and the explanation thereof is not repeated.  
       FIGS. 17 and 18  are sectional views schematically showing the configuration of the display element L i,j  to be the display cell in the display apparatus according to the sixth embodiment. The display element L i,j  according to this embodiment is similar to the first embodiment in that the first electrode-on-first-substrate (first electrode on the ECL side)  803  and the second electrode-on-first-substrate (second electrode on the ECL side)  804  are provided onto the first substrate  801  as shown in  FIGS. 17 and 18 . The sixth embodiment is different from the first embodiment in that an electrolyte layer  812  and the porous electrode or a porous electrode (first porous electrode)  816  including a porous material are provided between the second layer  807  and the first layer  806 .  
      The porous electrode (first porous electrode)  816  may be a composite membrane composed of a porous electrode (EC layer side) and a porous insulating film (electrolyte side). A pore diameter of the porous electrode (first porous electrode)  816  may fall within a range of 1 nm to 1000 nm, preferably a range of 1 nm to 100 nm. Various conductive materials (ITO, FTO, SnO 2  and the like) can be used, and thus it is not necessary that the pore shape and the pore diameter are uniform as long as the pore diameter falls within these ranges. The porous electrode (first porous electrode)  816  is normally made of an optically-transparent material so that the display can be observed. Examples of such an optically-transparent material are oxide of transition metal such as (compound) oxide of titanium (Ti), zirconium (Zr), hafnium (Hf), strontium (Sr), zinc (Zn), tin (Sn), indium (In), yttrium (Y), lanthanum (La), vanadium (V), niobium (Nb), tantalum (Ta), chromium (Cr), molybdenum (Mo) and tungsten (W) as metal oxide semiconductor, perovskite such as SrTiO 3 , CaTiO 3 , BlaTiO 3 , MgTiO 3  and SrNb 2 O 6 , compound oxide of them and oxide mixture, and gallium nitride (GaN). Examples of the optically-transparent material to be frequently used are an oxide indium (In 2 O 3 ) film (ITO) where tin (Sn) is doped, an oxide zinc (ZnO) film (IZN) where indium (In) is doped, an oxide zinc film (GZO) where gallium (Ga) is doped, and an oxide zinc film (FTO) where oxide tin (SnO 2 ) and fluorine for acid resistance are doped.  
      The material of the electrolyte layer  812  includes a solvent (when the first layer  806  is a liquid layer as the liquid electrolyte) or a gelled polymer which is swelled by this solvent (when the first layer  806  is a solid layer as a solid electrolyte) and a supporting electrolyte which is dissolved with the solvent or the polymer. Examples of the supporting electrolyte are tetrabutylammonium perchlorate, potassium hexafluorophosphate, lithium trifluoromethanesulfonate, lithium perchlorate, tetra-n-butylammonium tetrafluoroborate, tripropyl amine, and tetra-n-butylammonium fluoroborate.  
      Examples of the solvent are single solvent or mixed solvent composed of acetonitrile, N,N-dimethylformamide, propylene carbonate, o-dichlorobenzene, 1,2dimethoxyethane, glycerin, water, ethyl alcohol, propyl alcohol, dimethyl carbonate, ethylene carbonate, γ-butylolactone, N-methyl-2-pyrrolidone (NMP), 2-methyltetrahydrofuran, toluene, tetrahydrofuran, benzonitrile, cyclohexane, n-hexane, acetone, nitrobenzene, 1.3-dioxolan, furan, benzotrifuloride and the like.  
      Examples of the gelled polymer are a copolymer of polyacrylonitrile (PAN), vinylidene fluoride (VDF) and vinylidene hexafluoride (HFP), and polyethylene oxide (PEO).  
      In the display element L i,j  of the pixel X i,j  in the display apparatus according to the sixth embodiment, as shown in  FIG. 17 , the electrode on the first substrate side (the first electrode on the ECL side)  803  and the electrode on the first substrate side (second electrode on the ECL side)  804  are connected to the AC power supply circuit V ECL    210  via the switching element S 1 . They compose the first voltage applying unit ( 803 ,  804 , V ECL    210 ). The first electrode  803  on the first substrate side  803 , the second electrode-on-first-substrate  804  and the electrode-on-second-substrate (electrode on the EC side)  805  are connected to the DC power supplies E 1  and E 2  with different polarities via the switching element S 2 . They compose the second voltage applying unit ( 803 ,  804 ,  805 , E 1 ; E 2 ). The switching elements S 1  and S 2  selectively operate the first voltage applying unit ( 803 ,  804 , V ECL    210 ) and the second voltage applying unit ( 803 ,  804 ,  805 , E 1 , E 2 ).  
      The AC power supply circuit V ECL    210  has the similar configuration to that of the power supply circuit  210  in the first embodiment, and is composed of the counter voltage generating circuit  211 , the signal voltage generating circuit  212 , the variable resistor  213  and the switching element  214 . The circuit V ECL    210  applies an AC voltage between the first electrode-on-first-substrate  803  and the second electrode-on-first-substrate  804  so that the voltage waveform becomes trapezoid as shown in  FIG. 4 .  
      The counter voltage generating circuit  211  is connected to the first electrode-on-first-substrate  803 , and the signal voltage generating circuit  212  is connected to the second electrode-on-first-substrate  804  via the variable resistor  213  and the switching element  214 . Similarly to the first embodiment, when the AC voltage generated from the signal voltage generating circuit  212  is applied to the second electrode-on-first-substrate  804 , the AC voltage passes through the variable resistor  213 , so that while the voltage value is being gradually increased for the first period, the voltage is allowed to reach a predetermined voltage value at the time when the first period elapses. The predetermined voltage is maintained for the second period starting from the elapse of the first period. While the voltage is being gradually reduced for the third period starting from the elapse of the second period, the voltage is applied so that the voltage obtains a trapezoidal waveform where the value becomes 0 after elapse of constant period of time. Such application of the voltage is repeated so that the trapezoid wave where polarities differ alternately is obtained. In such a manner, the AC voltage of the trapezoid wave is applied.  
      In the luminous display of  FIG. 18 , the switching element S 2  is opened, and the first electrode-on-first-substrate  803 , the second electrode-on-first-substrate  804  and the electrode-on-second-substrate  805  are disconnected from the DC power supplies E 1  and E 2 . Further, the switching element S 1  is closed, and the first electrode-on-first-substrate  803  and the second electrode-on-first-substrate  804  are connected to the DC power supply circuit  210 . A DC voltage is, therefore, generated between the first electrode-on-first-substrate  803  and the second electrode-on-first-substrate  804  (via the porous electrode  816 ). The first layer  806  including the luminescent material emits light due to the voltage, and luminous color is observed. Similarly to  FIG. 17 , if a color filter is provided onto the first substrate of the pixel X i,j , the filter color is observed from the first substrate  801  side. When the application of the voltage from the DC power supply circuit  210  is stopped, the first layer  806  does not emit light, and thus the background color of the pixel X i,j , for example, black is displayed.  
      In the reflection display, the switching element S 1  is switched so that the first electrode-on-first-substrate  803  and the second electrode-on-first-substrate  804  short-circuit. The switching element S 2  is closed, and any of the DC power supplies E 1  and E 2  with different polarities are connected among the first electrode-on-first-substrate  803 , the second electrode-on-first-substrate  804  and the electrode-on-second-substrate  805  of the same electric potential. Therefore, the DC voltage is generated among the first electrode-on-first-substrate  803 , the second electrode-on-first-substrate  804  and the electrode-on-second-substrate  805  of the same electric potential, and the second layer  807  including the material showing the EC phenomenon is colored or becomes transparent. As a result, the second substrate  807  is observed as a background color via the colored second layer  807  or the transparent second layer  807  from the outside of the first substrate  801 . When the polarities of the applied voltages from the DC power supplies E 1  and E 2  are changed, the colored second layer  807  becomes transparent or the transparent second layer  807  is colored. As a result, the background color or the color of the second layer  807  is observed from the first substrate  801  side.  
      In the AC power supply circuit V ECL    210 , the AC voltage is applied between the first electrode-on-first-substrate  803  and the second electrode-on-first-substrate  804  by the switching operation of the variable resistor  213  and the switching element  214  repeatedly per constant cycle so that the voltage waveform for one cycle becomes trapezoid.  
      In the AC power supply circuit V ECL    210  of this embodiment, the counter voltage generating circuit  211  is connected to the first electrode-on-first-substrate  803 , and the signal voltage generating circuit  212  is connected to the second electrode-on-first-substrate  804  via the variable resistor  213  and the switching element  214 . On the contrary, however, the counter voltage generating circuit  211  may be connected to the second electrode-on-first-substrate  804 , and the signal voltage generating circuit  212  may be connected to the first electrode-on-first-substrate  803  via the variable resistor  213  and the switching element  214 .  
      In this embodiment, the variable resistor  213  is used in the AC power supply circuit V ECL    210  so that the voltage waveform becomes trapezoid. Instead of the variable resistor  213 , another circuit such as the low pass filter  313  shown in  FIG. 2  may be used so that the voltage waveform becomes trapezoid.  
      As shown in  FIG. 18 , the DC power supply circuit  210  composed of the counter voltage generating circuit  211  and the signal voltage generating circuit  212  may be connected so that the DC voltage is applied between the first electrode-on-first-substrate  803  and the second electrode-on-first-substrate  804 . The DC power supply circuit  210  has the similar configuration to that of the power supply circuit  210  in the first embodiment, and is composed of the DC power supply E ECL  including the counter voltage generating circuit  211  and the signal voltage generating circuit  212 , the variable resistor  213  and the switching element  214 . The circuit V ECL    210  applies a DC voltage between the first electrode-on-first-substrate  803  and the second electrode-on-first-substrate  804  so that the voltage waveform becomes trapezoid as shown in  FIG. 5 .  
      More specifically, the counter voltage generating circuit  211  is connected to the electrode on the first substrate side  803 , and the signal voltage generating circuit  212  is connected to the second electrode-on-first-substrate  804  via the variable resistor  213  and the switching element  214 . Similarly to the first embodiment, when the DC voltage generated from the signal voltage generating circuit  212  is applied to the second electrode-on-first-substrate  804 , the DC voltage passes through the variable resistor  213 , so that while the voltage value is being gradually increased for the first period (t 1 ) shown in  FIG. 4 , the voltage is allowed to reach a predetermined voltage value at the time when the first period elapses. The predetermined voltage is maintained for the second period (t 2 ) starting from the elapse of the first period. While the voltage is being gradually reduced for the third period (t 3 ) starting from the elapse of the second period, the voltage is applied so that the voltage obtains a trapezoidal waveform where the value becomes 0 after elapse of constant period of time. Such application of the voltage is repeated without changing polarity, so that the DC voltage of the trapezoid wave is applied.  
      In the DC power supply circuit  210 , the DC voltage is applied between the first electrode-on-first-substrate  803  and the second electrode-on-first-substrate  804  by the switching operation of the variable resistor  213  and the switching element  214  repeatedly per constant cycle so that the voltage waveform for one cycle becomes trapezoid as shown in  FIG. 5 .  
      In the DC power supply circuit  210  of this embodiment, the counter voltage generating circuit  211  is connected to the first electrode-on-first-substrate  803 , and the signal voltage generating circuit  212  is connected to the second electrode-on-first-substrate  804  via the variable resistor  213  and the switching element  214 . On the contrary, however, the counter voltage generating circuit  211  may be connected to the second electrode-on-first-substrate  804 , and the signal voltage generating circuit  212  may be connected to the first electrode-on-first-substrate  803  via the variable resistor  213  and the switching element  214 .  
      In this embodiment, the variable resistor  213  is used in the DC power supply circuit  210  so that the voltage waveform becomes trapezoid. Instead of the variable resistor  213 , another circuit such as the low pass filter  313  shown in FIG.  2  may be used so that the voltage waveform becomes trapezoid.  
      According to the display apparatus in the sixth embodiment, the reflection display and the luminous display can be realized by the simpler configuration than the fifth embodiment.  
      In the display apparatus according to the sixth embodiment, the AC power supply circuit V ECL    210  and the DC power supply circuit  210  repeat the application of the voltage with trapezoidal waveform to the display element. As a result, the light emission with high luminance by the display element can be realized for a longer period time in comparison with the case where the voltage with rectangular waveform is applied like the conventional display apparatuses.  
      A seventh embodiment is explained below.  
      In the display apparatus according to the seventh embodiment, an electrolyte layer and a porous electrode are further provided to the display element. In the display apparatus according to this embodiment, the configuration of the display element L i,j  of the pixel X i,j  is different from that in the first embodiment. As to the display apparatus according to the seventh embodiment, only different point from the first embodiment is explained, and like portions are designated by like reference numerals and the explanation thereof is not repeated.  
       FIGS. 19 and 20  are sectional views schematically showing the configuration of the display element L i,j  to be the display cell in the display apparatus according to the seventh embodiment. The display element L i,j  according to this embodiment is different from the first embodiment in that, as shown in  FIGS. 19 and 20 , the electrolyte layer  812  and the porous electrode or a porous electrode (first porous electrode)  816  including a porous material are provided between the second layer  807  and the first layer  806 .  
      The porous electrode (first porous electrode)  816  may be a composite membrane composed of a porous electrode (EC layer side) and a porous insulating film (electrolyte side). A pore diameter of the porous electrode (first porous electrode)  816  may fall within a range of 1 nm to 1000 nm, preferably a range of 1 nm to 100 nm. Various conductive materials (ITO, FTO, SnO 2  and the like) can be used, and thus it is not necessary that the pore shape and the pore diameter are uniform as long as the pore diameter falls within these ranges. The porous electrode (first porous electrode)  816  is normally made of an optically-transparent material so that the display can be observed. Examples of such an optically-transparent material are oxide of transition metal such as (compound) oxide of titanium (Ti), zirconium (Zr), hafnium (Hf), strontium (Sr), zinc (Zn), tin (Sn), indium (In), yttrium (Y), lanthanum (La), vanadium (V), niobium (Nb), tantalum (Ta), chromium (Cr), molybdenum (Mo) and tungsten (W) as metal oxide semiconductor, perovskite such as SrTiO 3 , CaTiO 3 , BlaTiO 3 , MgTiO 3  and SrNb 2 O 6 , compound oxide of them and oxide mixture, and gallium nitride (GaN). Examples of the optically-transparent material to be frequently used are an oxide indium (In 2 O 3 ) film (ITO) where tin (Sn) is doped, an oxide zinc (ZnO) film (IZO) where indium (In) is doped, an oxide zinc film (GZO) where gallium (Ga) is doped, and an oxide zinc film (FTO) where oxide tin (SnO 2 ) and fluorine for acid resistance are doped.  
      The material of the electrolyte layer  812  includes a solvent (when the first layer  806  is a liquid layer as the liquid electrolyte) or a gelled polymer which is swelled by this solvent (when the first layer  806  is a solid layer as a solid electrolyte) and a supporting electrolyte which is dissolved with the solvent or the polymer. Examples of the supporting electrolyte are tetrabutylammonium perchlorate, potassium hexafluorophosphate, lithium trifluoromethanesulfonate, lithium perchlorate, tetra-n-butylammonium tetrafluoroborate, tripropyl amine, and tetra-n-butylammonium fluoroborate.  
      Examples of the solvent are single solvent or mixed solvent composed of acetonitrile, N,N-dimethylformamide, propylene carbonate, o-dichlorobenzene, 1,2dimethoxyethane, glycerin, water, ethyl alcohol, propyl alcohol, dimethyl carbonate, ethylene carbonate, γ-butylolactone, N-methyl-2-pyrrolidone (NMP), 2-methyltetrahydrofuran, toluene, tetrahydrofuran, benzonitrile, cyclohexane, n-hexane, acetone, nitrobenzene, 1.3-dioxolan, furan, benzotrifuloride and the like.  
      Examples of the gelled polymer are a copolymer of polyacrylonitrile (PAN), vinylidene fluoride (VDF) and vinylidene hexafluoride (HFP), and polyethylene oxide (PEO). As shown in  FIG. 15 , the luminous display of the pixel X i,j  of the display apparatus according to seventh embodiment is performed by applying AC or DC voltage between the first electrode-on-first-substrate (first electrode on the ECL side)  803  and the second electrode-on-first-substrate  804  (second electrode on the ECL side). The reflection display is performed by applying the DC voltage among the first electrode-on-first-substrate  803 , the second electrode-on-first-substrate  804  (with the same electric potential) and the porous electrode (first porous electrode)  816 .  
      That is, in the pixel X i,j  of the display apparatus according to the seventh embodiment, as shown in  FIG. 19 , the first electrode-on-first-substrate  803  and the second electrode-on-first-substrate  804  are connected to the AC power supply circuit V ECL    210  via the switching element S 1 . They compose the first voltage applying unit ( 803 ,  803 , V ECL    210 ).  
      The first electrode-on-first-substrate  803 , the second electrode-on-first-substrate  804  and the porous electrode (first porous electrode)  816  are connected to the DC power supplies E 1  and E 2  with different polarities via the switching element S 2 . They compose the second voltage applying unit ( 803 ,  804 ,  805 , E 1 , E 2 ). The switching elements S 1  and S 2  selectively operate the first voltage applying unit ( 803 ,  804 , V ECL    210 ) and the second voltage applying unit ( 803 ,  804 ,  805 , E 1 , E 2 ).  
      The AC power supply circuit V ECL    210  has the similar configuration to that of the power supply circuit  210  in the first embodiment, and is composed of the counter voltage generating circuit  211 , the signal voltage generating circuit  212 , the variable resistor  213  and the switching element  214 . The circuit V ECL    210  applies an AC voltage between the first electrode-on-first-substrate  803  and the second electrode-on-first-substrate  804  so that the voltage waveform becomes trapezoid as shown in  FIG. 4 .  
      The counter voltage generating circuit  211  is connected to the first electrode-on-first-substrate  803 , and the signal voltage generating circuit  212  is connected to the second electrode-on-first-substrate  804  via the variable resistor  213  and the switching element  214 . Similarly to the first embodiment, when the AC voltage generated from the signal voltage generating circuit  212  is applied to the second electrode-on-first-substrate  804 , the AC voltage passes through the variable resistor  213 , so that while the voltage value is being gradually increased for the first period, the voltage is allowed to reach a predetermined voltage value at the time when the first period elapses. The predetermined voltage is maintained for the second period starting from the elapse of the first period. While the voltage is being gradually reduced for the third period starting from the elapse of the second period, the voltage is applied so that the voltage obtains a trapezoidal waveform where the value becomes 0 after elapse of constant period of time. Such application of the voltage is repeated so that the trapezoid wave where polarities differ alternately is obtained. In such a manner, the AC voltage of the trapezoid wave is applied.  
      In the luminous display by the display element L i,j  shown in  FIG. 19 , the switching element S 2  is opened, and the first electrode-on-first-substrate  803 , the second electrode-on-first-substrate  804  and the porous electrode (first porous electrode)  816  are disconnected from the DC power supplies E 1  and E 2 . Further, the switching element S 1  is closed, and the first electrode-on-first-substrate  803  and the second electrode-on-first-substrate  804  are connected to the AC power supply circuit V ECL    210 . An AC voltage is, therefore, generated between the first electrode-on-first-substrate  803  and the second electrode-on-first-substrate  804  (via the porous electrode  816 ). The first layer  806  including the luminescent material emits light due to the voltage, and luminous color is observed. If a color filter is provided onto the first substrate of the pixel X i,j , the filter color is observed from the first substrate  801  side. When the application of the voltage from the DC power supply circuit V ECL    210  is stopped, the first layer  806  does not emit light, and thus the background color of the pixel X i,j , for example, black is displayed.  
      In the AC power supply circuit V ECL    210  of this embodiment, the counter voltage generating circuit  211  is connected to the first electrode-on-first-substrate  803 , and the signal voltage generating circuit  212  is connected to the second electrode-on-first-substrate  804  via the variable resistor  213  and the switching element  214 . On the contrary, however, the counter voltage generating circuit  211  may be connected to the second electrode-on-first-substrate  804 , and the signal voltage generating circuit  212  may be connected to the first electrode-on-first-substrate  803  via the variable resistor  213  and the switching element  214 .  
      In this embodiment, the variable resistor  213  is used in the AC power supply circuit V ECL    210  so that the voltage waveform becomes trapezoid. Instead of the variable resistor  213 , another circuit such as the low pass filter  313  shown in  FIG. 2  may be used so that the voltage waveform becomes trapezoid.  
      As shown in  FIG. 20 , the DC power supply circuit  210  composed of the counter voltage generating circuit  211  and the signal voltage generating circuit  212  may be connected so that the DC voltage with trapezoidal waveform is applied between the first electrode-on-first-substrate  803  and the second electrode-on-first-substrate  804 . The DC power supply circuit  210  has the similar configuration to that of the power supply circuit  210  in the first embodiment, and is composed of the DC power supply E ECL  including the counter voltage generating circuit  211  and the signal voltage generating circuit  212 , the variable resistor  213  and the switching element  214 . The circuit V ECL    210  applies a DC voltage between the first electrode-on-first-substrate  803  and the second electrode-on-first-substrate  804  so that the voltage waveform becomes trapezoid.  
      More specifically, the counter voltage generating circuit  211  is connected to the first electrode-on-first-substrate  803 , and the signal voltage generating circuit  212  is connected to the second electrode-on-first-substrate  804  via the variable resistor  213  and the switching element  214 . Similarly to the first embodiment, when the DC voltage generated from the signal voltage generating circuit  212  is applied to the second electrode-on-first-substrate  804 , the DC voltage passes through the variable resistor  213 , so that while the voltage value is being gradually increased for the first period, the voltage is allowed to reach a predetermined voltage value at the time when the first period elapses. The predetermined voltage is maintained for the second period starting from the elapse of the first period. While the voltage is being gradually reduced for the third period starting from the elapse of the second period, the voltage is applied so that the voltage obtains a trapezoidal waveform where the value becomes 0 after elapse of constant period of time. Such application of the voltage is repeated without changing polarity, so that the DC voltage of the trapezoid wave is applied.  
      In the DC power supply circuit  210  of this embodiment, the counter voltage generating circuit  211  is connected to the first electrode-on-first-substrate  803 , and the signal voltage generating circuit  212  is connected to the second electrode-on-first-substrate  804  via the variable resistor  213  and the switching element  214 . On the contrary, however, the counter voltage generating circuit  211  may be connected to the second electrode-on-first-substrate  804 , and the signal voltage generating circuit  212  may be connected to the first electrode-on-first-substrate  803  via the variable resistor  213  and the switching element  214 .  
      In this embodiment, the variable resistor  213  is used in the DC power supply circuit  210  so that the voltage waveform becomes trapezoid. Instead of the variable resistor  213 , another circuit such as the low pass filter  313  shown in  FIG. 2  may be used so that the voltage waveform becomes trapezoid.  
      In the display cell L i,i  as shown in  FIG. 20 , the first electrode-on-first-substrate  803  and the second electrode-on-first-substrate  804  are connected to the DC power supply circuit  210  via the switching element S 1 . They compose the first voltage applying unit ( 803 ,  803 ,  210 ). Further, the first electrode-on-first-substrate  803 , the second electrode-on-first-substrate  804  and the porous substrate  816  are connected to the DC power supplies E 1  and E 2  with different polarities via the switching element S 2 . They compose the second voltage applying unit ( 803 ,  804 ,  805 , E 1 , E 2 ). The switching elements S 1  and S 2  compose the switching units (S 1  and S 2 ) that selectively operate the first voltage applying unit ( 803 ,  804 ,  210 ) and the second voltage applying unit ( 803 ,  804 ,  805 , E 1 , E 2 ).  
      In the luminous display of  FIG. 20 , the switching element S 2  is opened, and the first electrode-on-first-substrate  803 , the second electrode-on-first-substrate  804  and the porous electrode  816  are disconnected from the DC power supplies E 1  and E 2 . Further, the switching element S 1  is closed, and the first electrode-on-first-substrate  803  and the second electrode-on-first-substrate  804  are connected to the DC power supply circuit  210 . A DC voltage is, therefore, generated between the first electrode-on-first-substrate  803  and the second electrode-on-first-substrate  804  (via the porous electrode  816 ). The first layer  806  including the luminescent material emits light due to the voltage, and luminous color is observed. Similarly to  FIG. 19 , if a color filter is provided onto the first substrate  801  of the pixel X i,j , the filter color is observed from the first substrate  801  side. When the application of the voltage from the DC power supply circuit  210  is stopped, the first layer  806  does not emit light, and thus the background color of the pixel X i,j , for example, black is displayed.  
      In the reflection display, the switching element S 1  is switched so that the first electrode-on-first-substrate  803  and the second electrode-on-first-substrate  804  short-circuit. The switching element S 2  is closed, and any of the DC power supplies E 1  and E 2  with different polarities are connected between the first electrode-on-first-substrate  803 , the second electrode-on-first-substrate  804  and the porous electrode  816  with the same electric potential, respectively. Therefore, the DC voltage is generated between the first electrode-on-first-substrate  803 , the second electrode-on-first-substrate  804  and the porous electrode  816  with the same electric potential, and the electrolyte layer  812  including the material showing the EC phenomenon is colored or becomes transparent. As a result, the second substrate  802  is observed as a background color via the colored electrolyte layer  812  or the transparent electrolyte layer  812  from the outside of the first substrate  801 . When the polarities of the applied voltages from the DC power supplies E 1  and E 2  are changed, the colored electrolyte layer  812  becomes transparent or the transparent electrolyte layer  812  is colored. As a result, the background color or the color of the electrolyte layer  812  is observed from the first substrate  801  side.  
      According to the display apparatus in the seventh embodiment, the reflection display and the luminous display can be realized by the simpler configuration than the fifth embodiment.  
      In the display apparatus according to the seventh embodiment, the AC power supply circuit V ECL    210  and the DC power supply circuit  210  repeat the application of the voltage with trapezoidal waveform to the display element. As a result, the light emission with high luminance by the display element can be realized for a longer period of time in comparison with the case where the voltage with rectangular waveform is applied like the conventional display apparatuses.  
      An eighth embodiment is explained below.  
      In the display apparatus according to the eighth embodiment, as to the configuration of the display element, only a single electrode on the first substrate side is provided onto the first substrate  801 , and an intermediate electrode, an electrolyte layer and a porous layer are further provided. In the display apparatus according to this embodiment, the configuration of the display element L i,j  of the pixel X i,j  is different from that in the first embodiment. As to the display apparatus according to the eighth embodiment, only different point from the first embodiment is explained, and like portions are designated by like reference numerals and the explanation thereof is not repeated.  
       FIGS. 21 and 22  are sectional views schematically showing the configuration of the display element L i,j  to be the display cell in the display apparatus according to the eighth embodiment. The display element L i,j  according to this embodiment is, as shown in  FIGS. 21 and 22 , constituted so that only the electrode on the first substrate side  803  is provided onto the first substrate  801 , and the transparent intermediate layer  811 , electrolyte layer  812  and porous electrode (first porous electrode)  816  including a porous material are provided between the second layer  807  and the first layer  806 .  
      In the pixel X i,j  of the display apparatus according to the eighth embodiment, as shown in  FIG. 21 , the electrode-on-first substrate (electrode on the ECL side)  823  and the intermediate electrode  811  are connected to the DC power supply circuit  210  via the switching element S 5   d . The DC power supply circuit  210  is composed of the DC power supply E ECL    1  and the DC power supply E ECL    2  including the counter voltage generating circuit  211  and the signal voltage generating circuit  212 , the variable resistor  213  and the switching element  214 . The DC power supply circuit  210  is a circuit that applies a DC voltage between the electrode-on-first substrate  823  and the intermediate electrode  811  so that the voltage waveform becomes trapezoid. The DC power supplies E ECL    1  and E ECL    2  have different polarities. The DC power supply circuit  210 , the electrode-on-first substrate  823  and the intermediate electrode  811  compose the first voltage applying unit ( 823 ,  811 ,  210 ).  
      The counter voltage generating circuit  211  is connected to the electrode-on-first substrate  823 , and the signal voltage generating circuit  212  is connected to the intermediate electrode  811  via the variable resistor  213  and the switching element  214 . Similarly to the first embodiment, when the DC voltage generated from the signal voltage generating circuit  212  is applied to the intermediate electrode  811 , the voltage passes through the variable resistor  213 . While the voltage value is being gradually increased for the first period (t 1 ) as shown in  FIG. 4 , the voltage is allowed to obtain a predetermined voltage value at the time when the first period elapses. The predetermined voltage is maintained for the second period (t 2 ) starting from the elapse of the first period, and while the voltage value is being gradually decreased for the third period (t 3 ) starting from the elapse of the second period, the voltage is applied so as to obtain a trapezoidal waveform where the value becomes 0 after a constant period of time elapses. Such application is repeated without changing polarity, so that the DC voltage of trapezoid wave is applied.  
      The luminous display of the display cell L i,j  in the display apparatus according to the eight embodiment is performed by applying the AC or DC voltage between the electrode-on-first substrate  823  and the intermediate electrode  811 . That is, in the luminous display of the display cell L i,j  shown in  FIG. 21 , the switching element S 2  is opened, and the intermediate electrode  811  and the porous electrode  816  are disconnected from the power supplies E 1  and E 2 . Further, the switching element S 5   d  is closed with one of the polarities, and the electrode-on-first substrate  823  and the intermediate electrode  811  are connected to any of the DC power supplies E ECL    1  and E ECL    2  having different polarities, respectively. A DC voltage is, therefore, generated between the electrode-on-first substrate  823  and the intermediate electrode  811 , and the first layer  806  including the luminescent material emits light due to this voltage so that the luminescence color is observed. If a color filter is provided onto the first substrate  801  of the pixel X i,j , the filter color is observed from the first substrate  801  side. When the application of the voltage from the DC power supply circuit  210  is stopped, the first layer  806  does not emit light, and the background color of the pixel X i,j , for example, black is displayed.  
      In the DC power supply circuit  210  of this embodiment, the counter voltage generating circuit  211  is connected to the electrode-on-first substrate  823 , and the signal voltage generating circuit  212  is connected to the intermediate electrode  811  via the variable resistor  213  and the switching element  214 . On the contrary, however, the counter voltage generating circuit  211  may be connected to the intermediate electrode  811 , and the signal voltage generating circuit  212  may be connected to the electrode-on-first substrate  823  via the variable resistor  213  and the switching element  214 .  
      In this embodiment, the variable resistor  213  is used in the DC power supply circuit  210  so that the voltage waveform becomes trapezoid. Instead of the variable resistor  213 , another circuit such as the low pass filter  313  shown in FIG.  2  may be used so that the voltage waveform becomes trapezoid.  
      Meanwhile, in  FIG. 22 , the electrode-on-first substrate  823  and the intermediate electrode  811  are connected to the AC power supply circuit V ECL    210  via the switching element S 5   a . They compose the first voltage applying unit ( 823 ,  811 , V ECL    210 ). Further, the intermediate electrode  811  and the porous electrode (first porous electrode)  816  are connected to the DC power supplies E 1  and E 2  via the switching element S 2 . They compose the second voltage applying unit ( 811 ,  816 , E 1 , E 2 ). The switching elements S 5   a  and S 2  compose the switching units (S 5   a  and S 2 ) that selectively operate the first voltage applying unit ( 823 ,  811 , V ECL    210 ) and the second voltage applying unit ( 811 ,  816 , E 1 , E 2 ).  
      The AC power supply circuit V ECL    210  has the similar configuration to that in the first embodiment, and is composed of the counter voltage generating circuit  211 , the signal voltage generating circuit  212 , the variable resistor  213  and the switching element  214 . The circuit V ECL    210  applies an AC voltage between the electrode-on-first substrate  823  and the intermediate electrode  811  so that the voltage waveform becomes trapezoid as shown in  FIG. 4 .  
      More specifically, the counter voltage generating circuit  211  is connected to the intermediate electrode  811 , and the signal voltage generating circuit  212  is connected to the electrode-on-first substrate  823  via the variable resistor  213  and the switching element  214 . Similarly to the first embodiment, when the AC voltage generated from the signal voltage generating circuit  212  is applied to the electrode-on-first substrate  823 , the AC voltage passes through the variable resistor  213 , so that while the voltage value is being gradually increased for the first period, the voltage is allowed to reach a predetermined voltage value at the time when the first period elapses. The predetermined voltage is maintained for the second period starting from the elapse of the first period. While the voltage is being gradually reduced for the third period starting from the elapse of the second period, the voltage is applied so that the voltage obtains a trapezoidal waveform where the value becomes 0 after elapse of constant period of time. Such application of the voltage is repeated so that the polarities differ alternately, and thus the AC voltage of the trapezoid wave is applied.  
      In the AC power supply circuit V ECL    210 , the AC voltage is applied between the electrode-on-first substrate  823  and the intermediate electrode  811  by the switching operation of the variable resistor  213  and the switching element  214  repeatedly per constant cycle as shown in  FIG. 4  so that the voltage waveform for one cycle becomes trapezoid.  
      In the AC power supply circuit V ECL    210  of this embodiment, the counter voltage generating circuit  211  is connected to the intermediate electrode  811 , and the signal voltage generating circuit  212  is connected to the electrode-on-first substrate  823  via the variable resistor  213  and the switching element  214 . On the contrary, however, the counter voltage generating circuit  211  may be connected to the electrode-on-first substrate  823 , and the signal voltage generating circuit  212  may be connected to the intermediate electrode  811  via the variable resistor  213  and the switching element  214 .  
      In this embodiment, the variable resistor  213  is used in the AC power supply circuit V ECL    210  so that the voltage waveform becomes trapezoid. Instead of the variable resistor  213 , another circuit such as the low pass filter  313  shown in  FIG. 2  may be used so that the voltage waveform becomes trapezoid.  
      In this embodiment, the AC power supply circuit V ECL    210  applies the AC voltage between the electrode-on-first substrate  823  and the intermediate electrode  811 . However, the counter voltage generating circuit  211  and the signal voltage generating circuit  212  may be constituted so that the DC voltage is applied between the electrode-on-first substrate  823  and the intermediate electrode  811 .  
      In the luminous display of the display element L i,j  according to this embodiment shown in  FIG. 22 , the switching element S 2  is opened, and the intermediate electrode  811  and the porous electrode (first porous electrode)  816  are disconnected from the DC power supplies E 1  and E 2  with different polarities. Further, the switching element S 5   a  is closed, and the electrode-on-first substrate  823  and the intermediate electrode  811  are connected to the AC power supply circuit V ECL    210 . An AC voltage is, therefore, generated between the electrode on the first substrate side  803  and the intermediate electrode  811 , and the first layer  806  including the luminescent material emits light due to this voltage so that the luminescence color is observed. If a color filter is provided onto the first substrate  801  of the pixel X i,j , the filter color is observed from the first substrate  801  side. When the application of the voltage from the AC power supply circuit V ECL    210  is stopped, the first layer  806  does not emit light, and the background color of the pixel X i,j , for example, black is displayed.  
      The reflection display is performed by applying the DC voltage between the intermediate electrode  811  and the porous electrode (first porous electrode)  816 . In the reflection display, the switching element S 2  is closed, and the intermediate electrode  811  and the porous electrode (first porous electrode)  816  are connected to any of the DC power supplies E 1  and E 2  with different polarities, respectively. Therefore, the DC voltage is generated between the intermediate electrode  811  and the porous electrode (first porous electrode)  816  with the same electric potential, and the electrolyte layer  812  including the material showing the EC phenomenon is colored or becomes transparent. As a result, the second substrate  802  is observed as a background color via the colored electrolyte layer  812  or the transparent electrolyte layer  812  from the outside of the first substrate  801 . When the polarities of the applied voltages from the DC power supplies E 1  and E 2  are changed, the colored electrolyte layer  812  becomes transparent or the transparent electrolyte layer  812  is colored. As a result, the background color or the color of the electrolyte layer  812  is observed from the first substrate  801  side.  
      In the display apparatus according to the eighth embodiment, the user can select the luminous display or the reflection display.  
      In the display apparatus according to the eighth embodiment, the AC power supply circuit V ECL    210  and the DC power supply circuit  210  repeat the application of the voltage with trapezoidal waveform to the display element. As a result, the light emission with high luminance by the display element can be realized for a longer period of time in comparison with the case where the voltage with rectangular waveform is applied like the conventional display apparatuses.  
      A ninth embodiment is explained below.  
      In the display apparatus according to the ninth embodiment, as to the configuration of the display element, a porous electrode is provided between the first layer and the second layer. In the display apparatus according to this embodiment, the configuration of the display element L i,j  of the pixel X i,j  is different from that in the first embodiment.  
       FIG. 23  is a sectional view schematically showing a configuration of the display element L i,j  to be the display cell in the display apparatus according to the ninth embodiment. In the display element L i,j  according to this embodiment, as shown in  FIG. 23 , the porous electrode or a porous electrode (second porous electrode)  815  including a porous material are provided between the second layer  807  and the first layer  806 . The porous electrode (second porous electrode)  815  may be a composite membrane composed of a porous electrode (EC layer side) and a porous insulating film (electrolyte side). A pore diameter of the porous electrode (second porous electrode)  815  may fall within a range of 1 nm to 1000 nm, preferably a range of 1 nm to 100 nm. Various conductive materials (ITO, FTO, SnO 2  and the like) can be used, and thus it is not necessary that the pore shape and the pore diameter are uniform as long as the pore diameter falls within these ranges.  
      In the pixel X i,j  of the display apparatus according to the ninth embodiment, the luminous display is performed by applying the AC or DC voltage between the electrode-on-first substrate (electrode on the ECL side)  823  and the porous electrode (second porous electrode)  815 . That is, in the display element L i,j  provided with only the electrode on the first substrate side  803  shown in  FIG. 23 , as to the luminous display, the switching element S 2  is opened, the switching element S 6  is closed, and the AC voltage is applied between the electrode-on-first substrate  823  and the porous electrode (second porous electrode)  815 . As a result, the light emission can be observed on the first layer  806 .  
      The reflection display is performed by applying the DC voltage between the electrode-on-first substrate  823  and the electrode-on-second-substrate (electrode on the EC side)  805 . That is, in the reflection display, the switching element S 2  is closed, the switching element S 6  is opened, and any of the DC power supplies E 1  and E 2  with different polarities are connected to the electrode-on-first substrate  823  and the electrode-on-second-substrate  805 , respectively. A voltage (electric potential) for causing EC reaction is applied therebetween, so that coloring and bleaching are observed on the second layer  807 . When the polarities of the applied voltages from the DC power supplies E 1  and E 2  are changed, the colored second layer  807  becomes transparent or the transparent second layer  807  is colored. As a result, the background color or the color of the second layer  807  is observed from the first substrate  801  side.  
      The porous electrode (second porous electrode)  815  is normally made of an optically-transparent material so that the display can be observed. Examples of such an optically-transparent material are oxide of transition metal such as (compound) oxide of titanium (Ti), zirconium (Zr), hafnium (Hf), strontium (Sr), zinc (Zn), tin (Sn), indium (In), yttrium (Y), lanthanum (La), vanadium (V), niobium (Nb), tantalum (Ta), chromium (Cr), molybdenum (Mo) and tungsten (W) as metal oxide semiconductor, perovskite such as SrTiO 3 , CaTiO 3 , BlaTiO 3 , MgTiO 3  and SrNb 2 O 6 , compound oxide of them and oxide mixture, and gallium nitride (GaN). Examples of the optically-transparent material to be frequently used are an oxide indium (In 2 O 3 ) film (ITO) where tin (Sn) is doped, an oxide zinc (ZnO) film (IZO) where indium (In) is doped, an oxide zinc film (GZO) where gallium (Ga) is doped, and an oxide zinc film (FTO) where oxide tin (SnO 2 ) and fluorine for acid resistance are doped.  
      In this embodiment, as shown in  FIG. 23 , the electrode-on-first substrate  823  and the porous electrode (second porous electrode)  815  are connected to the AC power supply circuit V ECL    210  via the switching element S 6 . They compose the first voltage applying unit ( 823 ,  815 , V ECL    210 ). Further, the electrode-on-first substrate  823  and the electrode-on-second-substrate  805  are connected to the DC power supplies E 1  and E 2  with different polarities via the switching element S 2 . They compose the second voltage applying unit ( 823 ,  805 , E 1 , E 2 ). The switching elements S 6  and S 2  compose the switching units (S 6  and S 2 ) that selectively operate the first voltage applying unit ( 823 ,  815 , V ECL    210 ) and the second voltage applying unit ( 823 ,  805 , E 1 , E 2 ).  
      The AC power supply circuit V ECL    210  has the similar configuration to that in the first embodiment, and is composed of the counter voltage generating circuit  211 , the signal voltage generating circuit  212 , the variable resistor  213  and the switching element  214 . The circuit V ECL    210  applies an AC voltage between the electrode on the first substrate side  803  and the porous electrode  815  so that the voltage waveform becomes trapezoid as shown in  FIG. 4 .  
      The counter voltage generating circuit  211  is connected to the porous electrode  815 , and the signal voltage generating circuit  212  is connected to the electrode-on-first substrate  823  via the variable resistor  213  and the switching element  214 . Similarly to the first embodiment, when the AC voltage generated from the signal voltage generating circuit  212  is applied to the electrode-on-first substrate  823 , the AC voltage passes through the variable resistor  213 , so that while the voltage value is being gradually increased for the first period (t 1 ), the voltage is allowed to reach a predetermined voltage value at the time when the first period elapses. The predetermined voltage is maintained for the second period (t 2 ) starting from the elapse of the first period. While the voltage is being gradually reduced for the third period (t 3 ) starting from the elapse of the second period, the voltage is applied so that the voltage obtains a trapezoidal waveform where the value becomes 0 after elapse of constant period of time. Such application of the voltage is repeated so that the polarities differ alternately, and thus the AC voltage of the trapezoid wave is applied.  
      In the AC power supply circuit V ECL    210 , the AC voltage is applied between the electrode-on-first substrate  823  and the porous electrode  815  by the switching operation of the variable resistor  213  and the switching element  214  repeatedly per constant cycle as shown in  FIG. 4  so that the voltage waveform for one cycle becomes trapezoid.  
      In the AC power supply circuit V ECL    210  of this embodiment, the counter voltage generating circuit  211  is connected to the porous electrode  815 , and the signal voltage generating circuit  212  is connected to the electrode-on-first substrate  823  via the variable resistor  213  and the switching element  214 . On the contrary, however, the counter voltage generating circuit  211  may be connected to the electrode-on-first substrate  823 , and the signal voltage generating circuit  212  may be connected to the porous electrode  815  via the variable resistor  213  and the switching element  214 .  
      In this embodiment, the variable resistor  213  is used in the AC power supply circuit V ECL    210  so that the voltage waveform becomes trapezoid. Instead of the variable resistor  213 , another circuit such as the low pass filter  313  shown in  FIG. 2  may be used so that the voltage waveform becomes trapezoid.  
      In this embodiment, the AC power supply circuit V ECL    210  applies the AC voltage between the electrode-on-first substrate  823  and the porous electrode  815 . However, the counter voltage generating circuit  211  and the signal voltage generating circuit  212  may be constituted so that the DC voltage is applied between the electrode-on-first substrate  823  and the porous electrode  815 .  
      In the display apparatus according to the ninth embodiment, the user can select the luminous display or the reflection display in the simple configuration.  
      In the display apparatus according to the ninth embodiment, when the AC power supply circuit V ECL    210  repeats the application of the voltage of trapezoidal waveform to the display element, the light emission with high luminance can be maintained for a longer period of time in comparison with the case where a voltage with rectangular waveform is applied like conventional display apparatuses.  
      A tenth embodiment is explained below.  
      In the display apparatus according to the tenth embodiment, the first electrode-on-first-substrate as an electrode for ECL driving and the second electrode-on-first-substrate as an electrode for EC driving are provided onto the first substrate  801 . The first electrode-on-second-substrate as an electrode for ECL driving and a second electrode-on-second-substrate as an electrode for EC driving are provided onto the second substrate  802 , and the second layer is locally provided as the configuration of the display element.  
      In the display apparatus according to this embodiment, the configuration of the display element L i,j  of the pixel X i,j  is different from that in the first embodiment.  FIGS. 24 and 25  are sectional views schematically showing the configuration of the display element L i,j  to be the display cell in the display apparatus according to the tenth embodiment. The display element L i,j  according to this embodiment is, as shown in  FIGS. 24 and 25 , constituted so that a first electrode-on-first-substrate (first electrode for ECL driving)  817  and a second electrode-on-first-substrate (first electrode for EC driving)  819  are disposed on the first substrate  801 , and a first electrode-on-second-substrate (second electrode for ECL driving)  818  and a second electrode-on-second-substrate (second electrode for the EC driving)  820  are disposed on the second substrate  802 . Further, the first layer  806  is inserted between the first substrate  801  and the second substrate  802 , so as to be locally provided between the first layer  806  and the second electrode-on-second-substrate  820 .  
      Further, the second electrode-on-first-substrate  819  and the second electrode-on-second-substrate  820  are connected to the DC power supplies E 1  and E 2  with different polarities via the switching element S 2 . They compose the second voltage applying unit ( 819 ,  820 , E 1 , E 2 ). The switching elements S 7  and S 2  compose the switching units (S 7  and S 2 ) that selectively operate the first voltage applying unit ( 817 ,  818 ,  210 ) and the second voltage applying unit ( 819 ,  820 , E 1 , E 2 ).  
      The DC power supply circuit  210  has the similar configuration to that of the power supply circuit  210  in the first embodiment, and is composed of the DC power supply E ECL  including the counter voltage generating circuit  211  and the signal voltage generating circuit  212 , the variable resistor  213  and the switching element  214 . The circuit  210  applies a DC voltage between the first electrode-on-first-substrate  817  and the first electrode-on-second-substrate  818  so that the voltage waveform becomes trapezoid as shown in  FIG. 5 .  
      The counter voltage generating circuit  211  is connected to the first electrode-on-first-substrate  817 , and the signal voltage generating circuit  212  is connected to the first electrode-on-second-substrate  818  via the variable resistor  213  and the switching element  214 . Similarly to the first embodiment, when the DC voltage generated from the signal voltage generating circuit  212  is applied to the first electrode-on-second-substrate  818 , the DC voltage passes through the variable resistor  213 , so that while the voltage value is being gradually increased for the first period, the voltage is allowed to reach a predetermined voltage value at the time when the first period elapses. The predetermined voltage is maintained for the second period starting from the elapse of the first period. While the voltage value is being gradually reduced for the third period starting from the elapse of the second period, the voltage is applied so that the voltage obtains a trapezoidal waveform where the value becomes 0 after elapse of constant period of time. Such application of the voltage is repeated without changing polarities, so that the DC voltage of the trapezoid wave is applied.  
      In the DC power supply circuit  210 , the DC voltage is applied between the first electrode-on-first-substrate  817  and the first electrode-on-second-substrate  818  by the switching operation of the variable resistor  213  and the switching element  214  repeatedly per constant cycle as shown in  FIG. 5  so that the voltage waveform for one cycle becomes trapezoid.  
      In the DC power supply circuit  210  of this embodiment, the counter voltage generating circuit  211  is connected to the first electrode-on-first-substrate  817 , and the signal voltage generating circuit  212  is connected to the first electrode-on-second-substrate  818  via the variable resistor  213  and the switching element  214 . On the contrary, however, the counter voltage generating circuit  211  may be connected to the first electrode-on-second-substrate  818 , and the signal voltage generating circuit  212  may be connected to the first electrode-on-first-substrate  817  via the variable resistor  213  and the switching element  214 .  
      In this embodiment, the variable resistor  213  is used in the DC power supply circuit  210  so that the voltage waveform becomes trapezoid. Instead of the variable resistor  213 , another circuit such as the low pass filter  313  shown in  FIG. 2  may be used so that the voltage waveform becomes trapezoid.  
      Meanwhile, in the pixel X i,j  of the display apparatus according to the tenth embodiment shown in  FIG. 25 , the first electrode-on-first-substrate  817  and the first electrode-on-second-substrate  818  are connected to the AC power supply circuit V ECL    210  via the switching element S 7 . They compose the first voltage applying unit ( 817 ,  818 , V ECL    210 ). Further, the second electrode-on-first-substrate  819  and the second electrode-on-second-substrate  820  are connected to the DC power supplies E 1  and E 2  with different polarities via the switching element S 2 . They compose the second voltage applying unit ( 819 ,  820 , E 1 , E 2 ). The switching elements S 7  and S 2  compose the switching units (S 7  and S 2 ) that selectively operate the first voltage applying unit ( 817 ,  818 , V ECL    210 ) and the second voltage applying unit ( 819 ,  820 , E 1 , E 2 ).  
      The luminous display on the display element L i,j  of the pixel X i,j  of the display apparatus according to the tenth embodiment shown in  FIG. 25  is performed by applying the AC voltage between the first electrode-on-first-substrate  817  and the first electrode-on-second-substrate  818 . That is, in the configuration of the display element L i,j  shown in  FIG. 25 , as to the luminous display, the switching element S 2  is opened, the switching element S 7  is closed, and the AC voltage with a frequency which the EC reaction cannot follow is applied between the first electrode-on-first-substrate  817  and the first electrode-on-second-substrate  818 . As a result, the light emission is observed on the first layer  806 .  
      The reflection display is performed by applying the DC voltage between the second electrode-on-first-substrate  819  and the second electrode-on-second-substrate  820 . That is, in the reflection display, the switching element S 2  shown in  FIGS. 24 and 25  is closed, the switching element S 7  is opened, and any of the DC power supplies E 1  and E 2  with different polarities are connected between the second electrode-on-first-substrate  819  and the second electrode-on-second-substrate  820 . A voltage (electric potential) for causing EC reaction is applied therebetween, so that coloring and bleaching are observed on the second layer  807 . When the polarities of the applied voltages from the DC power supplies E 1  and E 2  are changed, the colored second layer  807  becomes transparent or the transparent second layer  807  is colored. As a result, the background color or the color of the second layer  807  is observed from the first substrate  801  side.  
      The AC power supply circuit V ECL    210  has the similar configuration to that of the power supply circuit  210  in the first embodiment, and is composed of the counter voltage generating circuit  211 , the signal voltage generating circuit  212 , the variable resistor  213  and the switching element  214 . The circuit V ECL    210  applies an AC voltage between the first electrode-on-first-substrate  817  and the first electrode-on-second-substrate  818  so that the voltage waveform becomes trapezoid as shown in  FIG. 4 .  
      More specifically, the counter voltage generating circuit  211  is connected to the first electrode-on-first-substrate  817 , and the signal voltage generating circuit  212  is connected to the first electrode-on-second-substrate  818  via the variable resistor  213  and the switching element  214 . Similarly to the first embodiment, when the AC voltage generated from the signal voltage generating circuit  212  is applied to the first electrode-on-second-substrate  818 , the AC voltage passes through the variable resistor  213 , so that while the voltage value is being gradually increased for the first period, the voltage is allowed to reach a predetermined voltage value at the time when the first period elapses. The predetermined voltage is maintained for the second period starting from the elapse of the first period. While the voltage value is being gradually reduced for the third period starting from the elapse of the second period, the voltage is applied so that the voltage obtains a trapezoidal waveform where the value becomes 0 after elapse of constant period of time. Such application of the voltage is repeated so that the trapezoid wave where polarity differs alternately. As a result, the AC voltage of the trapezoid wave is applied.  
      In the AC power supply circuit V ECL    210 , the AC voltage is applied between the first electrode-on-first-substrate  817  and the first electrode-on-second-substrate  818  by the switching operation of the variable resistor  213  and the switching element  214  repeatedly per constant cycle as shown in  FIG. 4  so that the voltage waveform for one cycle becomes trapezoid.  
      In the AC power supply circuit V ECL    210  of this embodiment, the counter voltage generating circuit  211  is connected to the first electrode-on-first-substrate  817 , and the signal voltage generating circuit  212  is connected to the first electrode-on-second-substrate  818  via the variable resistor  213  and the switching element  214 . On the contrary, however, the counter voltage generating circuit  211  may be connected to the first electrode-on-second-substrate  818 , and the signal voltage generating circuit  212  may be connected to the first electrode-on-first-substrate  817  via the variable resistor  213  and the switching element  214 .  
      In this embodiment, the variable resistor  213  is used in the AC power supply circuit V ECL    210  so that the voltage waveform becomes trapezoid. Instead of the variable resistor  213 , another circuit such as the low pass filter  313  shown in  FIG. 2  may be used so that the voltage waveform becomes trapezoid.  
      According to the display apparatus in the tenth embodiment, the reflection and the luminous display can be realized by the simple configuration. Further, in the display apparatus according to the tenth embodiment, when the AC power supply circuit V ECL    210  and the DC power supply circuit  210  repeat the application of the voltage of trapezoidal waveform to the display element, the light emission with high luminance can be maintained for a longer period of time in comparison with the case where a voltage with rectangular waveform is applied like conventional display apparatuses.  
      An eleventh embodiment is explained below.  
      In the configuration of the display element in the display apparatus according to the eleventh embodiment, a porous film is provided to the electrode on the first substrate side  803 . In the display apparatus according to this embodiment, the configuration of the display element L i,j  of the pixel X i,j  is different from that in the first embodiment.  
       FIG. 26  is a sectional view schematically showing the configuration of the display element L i,j  to be the display cell in the display apparatus according to the eleventh embodiment. In the display element L i,j  according to this embodiment, as shown in  FIG. 26 , a porous film  813  is provided to the electrode on the first substrate side (electrode on ECL side)  803 .  
      In the configuration of the display apparatus according to the third embodiment shown in  FIG. 12 , in the case of the reflection display, a small amount of ion radical species of the ECL material generated from the electrode on the first substrate side  803  and the second layer  807  react each other, and thus malfunction of light emission possibly occurs.  
      For this reason, in this embodiment, as shown in  FIG. 26 , the porous film  813  made of an electric conductor, a semiconductor or an insulator is provided onto the electrode on the first substrate side  803 , thereby preventing transfer (diffusion) of the ion radical species generated from the electrode first substrate side  803  to the second layer  807 . As a result, light emission (malfunction) due to the transfer (diffusion) of the ion radical species can be prevented.  
      A pore diameter of the porous film  813  may fall within a range of 1 nm to 1000 nm, preferably a range of 3 nm to 100 nm, and more preferably a range of 3 nm to 30 nm. Various electric conductors (ITO, FTO, SnO 2  and the like), semiconductors (TiO 2  and the like) or insulators (SiO 2  and the like) can be used, and thus it is not necessary that the pore shape and the pore diameter are uniform as long as the pore diameter falls within these ranges.  
      In the display apparatus according to this embodiment, the improvement in the light emission luminance on the electrode on the first substrate side  803  can be expected. This is because the ion radical species with different polarities which are generated from the electrode on the first electrode side  803  remain in the porous film  813  and do not diffuse into the electrolyte, so that the ion radical species collide, namely, emit light efficiently in the porous film  813 .  
      The AC power supply circuit V 3   210  in this embodiment, similarly to the third embodiment, applies an AC voltage with a frequency which the EC reaction cannot follow. The AC power supply circuit V 3   210  has the similar configuration to the power supply circuit  210  in the first embodiment, and is composed of the counter voltage generating circuit  211 , the signal voltage generating circuit  212 , the variable resistor  213  and the switching element  214 . The circuit V 3   210  applies an AC voltage between the electrode on the first substrate side  803  and the electrode-on-second-substrate  805  so that the voltage waveform becomes trapezoid as shown in  FIG. 4 .  
      More specifically, the counter voltage generating circuit  211  is connected to the electrode-on-second-substrate  805 , and the signal voltage generating circuit  212  is connected to the electrode on the first substrate side  803  via the variable resistor  213  and the switching element  214 . Similarly to the first embodiment, when the AC voltage generated from the signal voltage generating circuit  212  is applied to the electrode on the first substrate side  803 , the AC voltage passes through the variable resistor  213 , so that while the voltage value is being gradually increased for the first period (t 1 ) as shown in  FIG. 4 , the voltage is allowed to reach a predetermined voltage value at the time when the first period elapses. The predetermined voltage is maintained for the second period (t 2 ) starting from the elapse of the first period. While the voltage value is being gradually reduced for the third period (t 3 ) starting from the elapse of the second period, the voltage is applied so that the voltage obtains a trapezoidal waveform where the value becomes 0 after elapse of constant period of time. Such application of the voltage is repeated so that the trapezoid wave where polarity differs alternately. As a result, the AC voltage of the trapezoid wave is applied.  
      In the AC power supply circuit V 3   210 , the AC voltage is applied between the electrode on the first substrate side  803  and the electrode-on-second-substrate  805  by the switching operation of the variable resistor  213  and the switching element  214  repeatedly per constant cycle as shown in  FIG. 4  so that the voltage waveform for one cycle becomes trapezoid.  
      In the AC power supply circuit V 3   210  of this embodiment, the counter voltage generating circuit  211  is connected to the electrode-on-second-substrate  805 , and the signal voltage generating circuit  212  is connected to the electrode on the first substrate side  803  via the variable resistor  213  and the switching element  214 . On the contrary, however, the counter voltage generating circuit  211  may be connected to the electrode on the first substrate side  803 , and the signal voltage generating circuit  212  may be connected to the second electrode-on-second-substrate  805  via the variable resistor  213  and the switching element  214 .  
      In this embodiment, the variable resistor  213  is used in the AC power supply circuit V 3   210  so that the voltage waveform becomes trapezoid. Instead of the variable resistor  213 , another circuit such as the low pass filter  313  shown in  FIG. 2  may be used so that the voltage waveform becomes trapezoid.  
      In this embodiment, the AC voltage is applied by the AC power supply circuit V 3   210  between the electrode on the first substrate side  803  and the electrode-on-second-substrate  805 , but the counter voltage generating circuit  211  and the signal voltage generating circuit  212  may be constituted so that the DC voltage with trapezoidal waveform shown in  FIG. 5  is applied between the electrode of the first substrate side  803  and the electrode of the second substrate side  805 .  
      In the display apparatus according to the eleventh embodiment, the porous film  813  is provided onto the electrode on the first substrate side  803 , thereby preventing transfer (diffusion) of ion radical species generated from the electrode on the first substrate side  803  to the second layer  807  and light emission (malfunction) due to the transfer (diffusion) of the ion radical species in the case of the reflection display. In the case of the luminous display, the light emission luminance on the electrode on the first substrate side  803  can be improved.  
      In the display apparatus according to the eleventh embodiment, the AC power supply circuit V 3   210  repeats the application of the voltage with a trapezoidal waveform to the display element. As a result, the light emission with high luminance by the display element can be maintained for a longer period of time in comparison with the case where the voltage of rectangular waveform is applied like conventional display apparatuses.  
      An arrangement configuration of pixels in the display apparatus having the display element L i,j  according to the second to eleventh embodiments is explained below.  FIG. 28  is a plan view showing a part (portion of 2×2) of the pixel arrangement in the display apparatus having the display element L i,j  according to the second to the eleventh embodiment. The display apparatus according to the second to eleventh embodiments is, as shown in  FIG. 28 , constituted so that the pixels X i,j  are arranged in matrices two-dimensionally (i=1 to n; j=1 to m; n and m are positive integers). The matrices are composed of a plurality of first signal wirings B 1   j , B 1   j+1 , . . . and a plurality of second signal wirings B 2   j , B 2   j+1 , . . . which are laid in a vertical direction (column-wise direction), and a plurality of first scanning wirings W 1   i , W 1   i+1 , . . . and a plurality of second scanning wirings W 2   i , W 2   i+1 , . . . which extend to a horizontal direction (row direction) perpendicular to the first signal wirings B 1   j , B 1   j+1 , . . . and the second signal wirings B 2   j , B 2   j + 1 , . . . . Further, first power supply wirings P 1   j , P 1   j+1 , . . . and second power supply wirings P 2   j , P 2   j+1  . . . are laid so as to be parallel with the first signal wirings B 1   j , B 1   j+1  . . . and the second signal wirings B 2   j , B 2   j+1 .  
      As shown in  FIG. 28 , the first signal wiring B 1   j  is connected to a first terminal of a first writing transistor (TFT) Q 1   i,j , and the first scanning wiring W 1   i  is connected to a control terminal of the first wiring transistor Q 1   i,j . A second terminal of the first writing transistor Q 1   i,j  is connected to a control terminal of a first driving transistor (TFT) Q 2   i,j  and one terminal of a first auxiliary capacitor C 1   i,j . A first terminal of the first driving transistor Q 2   i,j  is connected to the first power supply wiring P 1   j , a second terminal of the first driving transistor Q 2   i,j  is connected to the display cell L i,j . The other end of the first auxiliary capacitor C 1   i,j  is grounded. The “first terminal” means a terminal to be any one of an emitter terminal and a collector terminal in a bipolar transistor (BJT). In a field-effect transistor (FET) and a static induction transistor (SIT), the “first terminal” means to be any one of a source terminal and a drain terminal. The “second terminal” means a terminal to be any one of an emitter terminal and a collector terminal which is not the first terminal in BJT or the like, and means a terminal to be any one of the source terminal and the drain terminal in FET and SIT which is not the first terminal. That is, when the first terminal is the emitter terminal, the second terminal is the collector terminal, and when the first terminal is the source terminal, the second terminal is the drain terminal. The “control terminal” means a terminal for controlling an electric current flowing between the first terminal and the second terminal, a Schottky key junction terminal, a terminal of an insulating gate structure or its structure. For example, the “control terminal” means a gate terminal or a gate structure in FET and SIT, and means a base terminal in BJT. In TFT or the like generally, since the first terminal and the second terminal have symmetrical configurations, it is simply a matter of selection as to which is called as the source terminal or the drain terminal or which is called as the emitter terminal or the collector terminal. The second signal wiring B 2   j  is connected to a first terminal of a second wiring transistor (TFT) Q 3   i,j , and the second scanning wiring W 2   i  is connected to a control terminal of a second writing transistor Q 3   i,j . A second terminal of the second writing transistor Q 3   i,j  is connected to a control terminal of a second driving transistor (TFT) Q 4   i,j  and one terminal of a second auxiliary capacitor C 2   i,j . A first terminal of a second driving transistor (TFT) Q 4   i,j  is connected to a second power supply wiring P 2   j , and a second terminal of the second driving transistor Q 4   i,j  is connected to the display cell L i,j . The other terminal of the second auxiliary capacitor C 2   i,j  is grounded.  
      The first signal wiring B 1   j  is connected to a first terminal of the first writing transistor (TFT) Q 1   i+1,j , and a first scanning wiring W 1   i+1  is connected to a control terminal of the first writing transistor Q 1   i+1,j . A second terminal of the first wiring transistor Q 1   i+,j  is connected to a control terminal of a first driving transistor (TFT) Q 2   i+1,j  and one terminal of a first auxiliary capacitor C 1   i+1,j . A first terminal of the first driving transistor Q 2   i+1,j  is connected to the first power supply wiring P 1   j , and a second terminal of the first driving transistor Q 2   i+1,j  is connected to the display cell L i+1,j . The other terminal of the first auxiliary capacitor C 1   i+1,j  is grounded. The second signal wiring B 2   j  is connected to a first terminal of a second wiring transistor (TFT) Q 3   i+1,j , and the second scanning wiring W 2   i+1  is connected to a control terminal of the second writing transistor Q 3   i+1,j . A second terminal of the second writing transistor Q 3   i+1,j  is connected to a control terminal of a second driving transistor (TFT) Q 4   i+1,j  and one terminal of a second auxiliary capacitor C 2   i+1,j . A first terminal of the second driving transistor Q 4   i+1,j  is connected to the second power supply wiring P 2   j , and a second terminal of the second driving transistor Q 4   i+1,j  is connected to the display cell L i+1,j . The other terminal of the second auxiliary capacitor C 2   i+1,j  is grounded.  
      The first signal wiring B 1   j+1  is connected to a first terminal of a first writing transistor (TFT) Q 1   i,j+1 , and the first scanning wiring W 1   i  is connected to a control terminal of the first writing transistor Q 1   i,j+1 . A second terminal of the first writing transistor Q 1   i,j+1  is connected to a control terminal of a first driving transistor (TFT) Q 2   i,j+1  and one terminal of a first auxiliary capacitor C 1   i,j+1 . A first terminal of the first driving transistor Q 2   i,j+1  is connected to the first power supply wiring P 1   j+1 , and a second terminal of the first driving transistor Q 2   i,j+1  is connected to the display cell L i,j+1 . The other terminal of the first auxiliary capacitor C 1   i,j+1  is grounded. The second signal wiring B 2   j+1  is connected to a first terminal of a second writing transistor (TFT) Q 3   i,j+1 , and the second scanning wiring W 2   i  is connected to a control terminal of the second writing transistor Q 3   i,j+1 . A second terminal of the second writing transistor Q 3   i,j+1  is connected to a control terminal of a second driving transistor (TFT) Q 4   i,j+1  and one terminal of the second auxiliary capacitor C 2   i,j+1 . A first terminal of the second driving transistor Q 4   i,j+1  is connected to the second power supply wiring P 2   j+1 , and a second terminal of the second driving transistor Q 4   i,j+1  is connected to the display cell L i,j+1 . The other terminal of the second auxiliary capacitor C 2   i,j+1  is grounded.  
      Further, the first signal wiring B 1   j+1  is connected to a first terminal of a first writing transistor (TFT) Q 1   i+1,j+1 , and the first scanning wiring W 1   i+1  is connected to a control terminal of the first writing transistor Q 1   i+1,j+1 . A second terminal of the first writing transistor Q 1   i+1,j+1  is connected to a control terminal of a first driving transistor (TFT) Q 2   i+1,j+1  and one terminal of a first auxiliary capacitor C 1   i+1,j+1 . A first terminal of the first driving transistor Q 2   i+1,j+1  is connected to the first power supply wiring P 1   j+1 , and a second terminal of the first driving transistor Q 2   i+1,j+1  is connected to the display cell L i+1,j+1 . The other end of the first auxiliary capacitor C 1   i+1,j+1  is grounded. The second signal wiring B 2   j+1  is connected to a first terminal of a second writing transistor (TFT) Q 3   i+1,j+1 , and the second scanning wiring W 2   i+1  is connected to a control terminal of the second writing transistor Q 3   i+1,j+1 . A second terminal of the second writing transistor Q 3   i+1,j+1  is connected to a control terminal of a second driving transistor (TFT) Q 4   i+1,j+1  and one terminal of a second auxiliary capacitor C 2   i+1,j+1 . A first terminal of the second driving transistor Q 4   i+1,j+1  is connected to the second power supply wiring P 2   j+1 , and a second terminal of the second driving transistor Q 4   i+,j+1  is connected to the display cell L i+1,j+1 . The other terminal of the second auxiliary capacitor C 2   i+1,j+1  is grounded.  
      As the first writing transistors Q 1   i,j , Q 1   i+1,j , Q 1   i,j+1 , and Q 1   i+1,j+1 , the first driving transistors Q 2   i,j , Q 2   i+1,j , Q 2   i,j+1 , and Q 2   i+1,j+1 , the second writing transistors Q 3   i,j , Q 3   i+1,j , Q 3   i,j+1  and Q 3   i+1,j+1 , and the second driving transistors Q 4   i,j , Q 4   i+1,j , Q 4   i,j+1 , and Q 4   i+1,j+1 , TFTs which are used for an active matrix substrate used in LCD and organic EL may be used.  
      The first scanning wirings W 1   i , W 1   i+1 , . . . and the first signal wirings B 1   j , B 1   j+1 , . . . are synchronized with each other so that voltages are applied, and display signals from the first writing transistors Q 1   i,j , Q 1   i+1,j , Q 1   i,j+1 , Q 1   i+1,j+1 , . . . are accumulated in the first auxiliary capacities C 1   i,j , C 1   i+1,j , C 1   i,j+1, C1   i+1,j+1 , . . . . The first driving transistors Q 2   i,j , Q 2   i+1,j , Q 2   i,j+1 , Q 2   i+,j+1 , . . . can control the amount of electric current to flow in the display cells L i,j , L i+1,j , L i,j+1  and L i+1,j+1  according to the amount of electric charges of the display signals in the first auxiliary capacities C 1   i,j , C 1   i+1,j , C 1   i,j+1 , C 1   i+1,j+1 , . . . . Similarly, the second scanning wirings W 2   i , W 2   i+1 , . . . and the second signal wirings B 2   j , B 2   j+1 , . . . are synchronized with each other so that voltages are applied, and display signals from the second writing transistors Q 3   i,j , Q 3   i+1,j , Q 3   i,j+1 , Q 3   i+1,j+1 , . . . are accumulated in the second auxiliary capacities C 2   i,j , C 2   i+1,j , C 2   i,j+1 , C 2   i+1,j+1 , . . . . The second driving transistors Q 4   i,j , Q 4   i+1,j , Q 4   i,j+1 , Q 4   i+,j+1 , . . . can control the amount of electric current to flow in the display cells L i,j , L i+1,j , L i,j+1 , and L i+1,j+1  according to the amount of electric charges of the display signals in the second auxiliary capacities C 2   i,j , C 2   i+1,j , C 2   i,j+1 , C 2   i+1,j+1 , . . . .  
      As a result, the electric current which flows in the display cells L i,j , L i+1,j , L i,j+1 , and L i+1,j+1  supplied from the first power supply wirings P 1   j , P 1   j+1 , . . . and the second power supply wirings P 2   j , P 2   j+1 , . . . is switched, so that display can be performed while both the reflection display and the luminous display are being switched.  
      [Method of Manufacturing the Display Apparatus] 
      The method of manufacturing the above-explained display apparatus is explained by exemplifying the display apparatus according to the second embodiment. The method of manufacturing the display apparatus explained below is one example, and needless to say, the manufacturing method including this modified example can be realized by various manufacturing methods other than the following method.  
      (1) Substrates with thickness of 0.7 mm made of glass are used as the first substrate  801  and the second substrate  802 , and ITO with film thickness of 100 nm is formed by sputtering. ITO is patterned so that the first electrode-on-first-substrate  803 , the second electrode-on-first-substrate  804  and the electrode-on-second-substrate  805  are formed.  
      (2) After a surface of the second substrate  802  formed with the electrode-on-second-substrate  805  is subject to UV process, the surface is spin-coated with previously synthesized polytungsten peroxide solution containing tungsten 4 mol/l, and an EC layer (W 1 O 3  film) to be the second layer  807  is formed so as to have a thickness of about 100 nm.  
      (3) The first substrate  801  and the second substrate  802  are arranged in an opposed manner via a glass beads spacer with particle diameter of 2 μm so as to have a gap of 2 μm, and their circumference excluding an filling opening is hardened by epoxy resin so that a cell is formed.  
      (4) Lithium salt (LiCF 3 SO 3 ) of 10 mM and TBAPF 6  (tetra-n-butylammoniumhexafluorophosphate) are dissolved in o-dichlorobenzene/acetonitrile mixed solvent (3/1) so that an electrolyte is formed as a supporting electrolyte. Rubrene of 10 mM as an ECL material is dissolved in the electrolyte, and it is injected into the cell so that the first layer (ECL electrolyte layer)  806  is formed. A previously created reflection plate made of Al and the cell are laminated so that the display apparatus is completed.  
      The display apparatus according to the second embodiment is exemplified based on the above-explained display apparatus, and its operation is explained. The 2.5 inch display apparatus was manufactured by using the above method of manufacturing the display apparatus. The display cell L i,j  of each pixel X i,j  has the configuration shown in  FIG. 8  composed of a single-color electrochemical reaction element, and the display apparatus was manufactured so that the size of one pixel X i,j  became 100 μm. The first electrode-on-first-substrate  803  and the second electrode-on-first-substrate  804  had the same electric potential, and a voltage was applied between the electrodes  803  and the electrode  804  and the electrode-on-second-substrate  805 . As a result, the polarities of the applied voltages were selected and the voltage was applied so that the electrode-on-second-substrate  805  became positive, and thus a bleached state was realized.  
      Further, the polarity of the applied voltage was selected and the voltage was applied so that the electrode-on-second-substrate  805  becomes negative. As a result, a blue-colored state was realized, and it was found that reflection display was possible.  
      The voltage was not applied to the electrode-on-second-substrate  805 , and an AC voltage with rectangular wave of 20 Hz was applied between the first electrode-on-first-substrate  803  and the second electrode-on-first-substrate  804 . As a result, yellow light emission was observed.  
      Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.