Abstract:
An electrochromic device with high transmittance is for use as a display device. The electrochromic device includes at least a first and a second electrode formed on an insulative substrate and a conductive layer formed in contact with the insulative substrate, the first electrode, and the second electrode. Since an electrode layer functions in one layer, the transmittance through the device is enhanced, and the device can be fabricated in a simple process, allowing a reduction in the device fabrication costs.

Description:
CLAIM OF PRIORITY  
       [0001]     The present application claims the benefit under 35 U.S.C. § 119 of the earlier filing date of Japanese Patent Application JP 2004-212460 which was filed on Jul. 21, 2004, the content of which is hereby incorporated by reference into the present application.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a display and a method for displaying information with the use of electrochromism.  
         [0004]     2. Description of the Background  
         [0005]     “Electrochromism”, a phenomenon in which a compound color reversibly changes by applying a voltage, has been applied to electrochromic window glass and display devices. As shown below, conventionally known electrochromic devices have a structure in which an electrochromic layer and an electrolyte layer are sandwiched between a pair of electrodes, at least one of which being a transparent electrode, and electrochromism is generated by a voltage applied between these electrodes. This conventional structure is disclosed, for example, in Japanese Patent Application JP-A No. 287173/2002 (hereafter “Patent document 1”).  
         [0006]     Further, Japanese Patent Application JP-A No. 50406/2003 (hereafter “Patent Document 2”) discloses electrochromic glass in which an electrochromic layer, an electrolyte film, and an ion storage layer are sandwiched between a pair of transparent conductor layers (electrodes). This conventional technology makes use of indium-tin oxide (ITO) and fluorine-doped tin oxide (FTO) as the transparent electrodes or the transparent conductors.  
         [0007]     Moreover, a multi-layer optical disk in which the electrochromic layer is formed in a multi-layer structure and the layer selection is carried out by voltage application has been reported by the present inventors in Proc. SPIE, 5069, 300-305, 2003 (“Non-Patent Document 1”). This multi-layer optical disk is fabricated by making a unit structure provided with an electrochromic layer and an electrolyte layer between a pair of transparent electrodes in a manner similar to that in Patent Document 2 and then laminating a plurality of these unit structures.  
         [0008]     Another display device making use of the principle of electrochromism is disclosed in Japanese Patent Application JP-A No. 82360/2002 (“Patent Document 3”). Likewise, an optical disk that records information by allowing coloration of a reflective layer by means of electrochromism is disclosed in Japanese Patent Application JP-A No. 185288/1999 (“Patent Document 4”). Finally, an information recording medium in which a voltage is applied above and below the recording layer colored by electrochromism and in which information recording is carried out is disclosed in Japanese Patent Application JP-A No. 346378/2003 (“Patent Document 5”).  
       SUMMARY OF THE INVENTION  
       [0009]     In the electrochromic display disclosed in Patent Document 1 and the above-described multi-layer optical disk reported in Non-Patent Document 1, an enhancement of the efficiency of light utilization to the greatest extent possible requires that the transmittance through the transparent electrode layers approximate to 100%. At the same time, low electric resistance is required for these layers to be used as electrodes. However, the transparent electrode is known to have absorption in the visible region, and the transmittance of 100% has not yet been achieved for the transparent electrode. One purpose of the present invention is to address these problems and achieve an electrochromic device structure with high transmittance.  
         [0010]     As described above, the transparent electrode has absorption in the visible region and a transmittance of 100% has not yet been achieved for the transparent electrode. This can be explained by the principle of conductivity development in a transparent electrode material as described below. The conductivity of a compound used for a transparent electrode such as ITO is given by the definitional equation of electric conductivity (Equation 1): 
 
σ= neμ   (Equation 1) 
 
 where σ is the electric conductivity, n is a carrier concentration, e is an electric charge of an electron, and μ is mobility of the carrier. Since electric conductivity is discussed, the carrier represents free electrons in this case. What is involved in light absorption by the transparent electrode here is the carrier concentration n. 
 
         [0011]     A decrease in electric resistance of indium oxide (In 2 O 3 ), tin oxide (SnO 2 ), and similar materials is achieved by enhancing the carrier density by means of adding a dopant such as tin (Sn) or aluminum (Al) to each of these materials to generate a defect in their crystal lattice. On the other hand, an increase of free electrons, the carrier in the transparent electrode, causes absorption of light having a frequency lower than that of plasma oscillation, which obviously trades off the transparency of the electrode. The plasma frequency ω is represented by (Equation 2): 
 
ω= ne   2 /ε 0 ε ∞   m   ∞   (Equation 2) 
 
 where n is the carrier concentration, ε ∞  is an optical dielectric constant, and m ∞  is an optically effective mass. As n increases, ω also increases, and light from the near-infrared to the visible region tends to be absorbed. 
 
         [0012]     In addition to the inherent trade-off relationship between electric conductivity and transparency, there is a limit in increasing the carrier concentration. For example, a decrease of resistance of the transparent electrode to no more than 30 Ω/sq in terms of sheet resistance presents the problems of not only the thickening of the electrode layer needed but also that the transparency must be sacrificed. The relationship among sheet resistance, transmittance, and film thickness of ITO film is shown in the monthly journal, Display, September issue, p. 46 (1996). For example, it has been reported that when a sputtering method, a typical method for ITO film fabrication, is used, the thickness and the transmittance at a wavelength of 550 nm for an ITO film having an average sheet resistance of 100 Ω/sq are 30±15 nm and 81% or higher, respectively, and those for an ITO film of 6 Ω/sq are 220±20 nm and 75% or higher, respectively.  
         [0013]     At this point, the constitution of the present invention to solve the above problem is described. An electrochromic device used for the display of the present invention is constructed as shown in the cross sectional structure in  FIG. 1A . A conductive layer  7  is formed so as to be in contact with both a first electrode  2  and a second electrode  3  that are fabricated on an insulative substrate  1  and are insulated from each other. In other words, the display according to the present invention has features that an insulative member, the first electrode and the second electrode formed in the same plane as the insulative member surface, and the conductive layer containing an electrochromic material arranged so as to be conductive with the first electrode and the second electrode are provided. An electrochromic device in which the first electrode and the second electrode are insulated from each other is displayed as a pixel. Namely, owing to this structure, the display device used for the display according to the present invention has one fewer electrode layer compared with a conventional display device, thereby enabling the reduction of the decay of the amount of light. Specific details of this structure follow.  
         [0014]     The features of the electrochromic device used for the display of the present invention are compared to those of a conventionally known device shown in  FIG. 13 . The device of the present invention and the conventional device are both transparent type, and the same materials for the substrate, electrodes, electrochromic layer, and electrolyte layer are used for both devices, and these layers have the same thickness, respectively. The substrate is glass and the electrode used is ITO. Although the ITO film forms a transparent electrode, it absorbs light. The conventional electrochromic device has a structure in which an electrochromic layer  353  and an electrolyte layer  354  are sandwiched between a pair of a first electrode  351  and a second electrode  352 . A voltage is supplied between the first electrode  351  and the second electrode  352  from a power source  355 , thereby carrying out coloration of the device. This device is inevitably viewed through the electrode layer when viewed from either side of the first electrode  351  or the second electrode  352 . On the other hand, the device of the present invention shown in  FIGS. 1 and 2  has a structure having one fewer electrode layer, and thus its fabrication process can be simplified. Further, when the device of the present invention is viewed from the side opposite to the substrate, light without passing through an electrode layer can be seen, thereby enabling to reduce the decay of light amount. Furthermore, since ITO or ITO substrate is expensive, there is also an advantage that the device cost can be cut by decreasing electrode layers to be used.  
         [0015]     The display with the use of the electrochromic device of the present invention is compared with the conventionally known display with the use of the electrochromic device shown in  FIG. 13 . ITO, that is most frequently used for a transparent electrode, in fact absorbs light, and therefore, light amount decays by passing through the ITO layer in the conventional structure ( FIG. 13 ). However, the decay of light amount can be reduced in the electrochromic device of the present invention because light, without passing through the electrode layer, can be seen when viewed from the side opposite to the substrate. Furthermore, since ITO or an ITO substrate is expensive, there is also an advantage that the device cost can be cut by decreasing electrode layers to be used.  
         [0016]     As for an effect characteristic of a display, the display having the conventional structure is generally provided with a cover layer and a protective layer to protect the ITO electrode layer, and the material used for the protective layer is typically glass (refractive index, ca. 1.5) or a polymer such as PET (refractive index, ca. 1.5). Therefore it becomes difficult to see display pixels due to light reflection caused by the difference of refractive index between the protective layer and the ITO electrode (refractive index, ca. 2.0) in this case. For example, when light enters from a glass layer with a refractive index of 1.54 into an ITO layer with a refractive index of 2.0, surface reflectivity R on the ITO layer is derived by the following equation: 
 
 R (%)=((2.0−1.54)/(2.0+1.54)) 2 ×100=1.69(%) 
 
         [0017]     On the other hand, when the display of the present invention is viewed from the opposite side  727  to a substrate  721  having electrodes  722 ,  723  as shown in  FIG. 35 , light reflection can be suppressed because reflectivities of both polymer electrolyte and conductive polymer used for the electrochromic layer generally range from 1.4 to 1.6 and can be conformed approximately to the reflectivity of the protective layer.  
         [0018]     Hereinafter, the constitution of the present invention is specifically described. The electrochromic device of the present invention is constructed as shown in the cross sectional structure in  FIG. 1A . The conductive layer  7  is formed so as to be in contact with both the first electrode  2  and the second electrode  3  that are fabricated on the insulative substrate  1  and insulated from each other. In other word, the display according to the present invention has the features that the insulative member, the first electrode and the second electrode formed in the same plane as the insulative member surface, and the conductive layer containing an electrochromic material arranged so as to be conductive with the first electrode and the second electrode are provided and that the electrochromic device in which the first electrode and the second electrode are insulated from each other is displayed as a pixel.  
         [0019]     Furthermore, the conductive layer  7  has a bilayer structure composed of an electrochromic layer and an electrolyte layer in the parallel direction with respect to the arrangement of the first electrode  2  and the second electrode  3 . As for this bilayer structure, two mutually different structures are possible. Specifically in a first structure, an electrochromic layer  4  is formed in contact with both the first electrode  2  and the second electrode  3  as shown in the cross sectional structure in  FIG. 1B . Further, an electrolyte layer  5  is formed on the electrochromic layer  4  so as not to make contact with the insulative substrate  1 , the first electrode  2 , or the second electrode  3 . Voltage supply is possible from a power source  6  via wiring between the first electrode  2  and the second electrode  3 .  
         [0020]     Another structure with the reversed lamination order shown in  FIG. 2  is also possible for the bilayer structure of the conductive layer  7 . Hereinafter, the structure shown in  FIG. 1B  is referred to as the “first structure” and the structure shown in  FIG. 2  is referred to as the “second structure”, respectively. In the device having the second structure shown in  FIG. 2 , an electrolyte layer  104  is formed in contact with both a first electrode  102  and a second electrode  103  fabricated on an insulative substrate  101 . Further, an electrochromic layer  105  is formed on the electrolyte layer  104  so as not to make contact with the insulative substrate  101 , the first electrode  102 , or the second electrode  103 . Voltage supply is possible from a power source  106  via wiring between the first electrode  102  and the second electrode  103 .  
         [0021]     When the device shown in  FIG. 1B  is viewed from above the electrolyte layer  5 , the structure is that shown in  FIG. 3 . On an insulative substrate  11 , a first electrode  12  and a second electrode  13  are present, and the electrochromic layer and an electrolyte layer  14  are layered thereon. Here, the electrochromic layer is present underneath the electrolyte layer  14 . Wiring from a power source  15  connects between the first electrode  12  and the second electrode  13 . For the insulative substrate  11 , an inorganic material such as glass, quartz, or sapphire or a polymer material such as polyethylene, polypropylene, poly(ethylene terephthalate) (PET), polyolefin, or acrylate resin is preferably used. Glass is a preferred material among these, while the use of a polymer material such as PET allows the device to have a curvature.  
         [0022]     For the first electrode and the second electrode, a metal oxide such as indium tin oxide (ITO), indium oxide (In 2 O 3 ), fluorine-doped tin oxide (FTO), tin oxide (SnO 2 ), or indium zinc oxide (IZO) or a metal such as aluminum, gold, silver, copper, palladium, chrome, platinum, or rhodium is preferably used. Among them, metal oxide compounds are high in transmittance, and the use of a transparent insulative substrate makes it possible for the whole device to have transparency. Metal such as aluminum, gold, and chrome are high in reflectivity of visible light, thereby allowing the preparation of a reflective type electrochromic device.  
         [0023]     The first electrode and the second electrode are electrically separated from each other by a distance of from 1 μm to 1 cm. For the electrochromic layer, at least one material selected from an electrochromic material of conductive polymer, an electrochromic material of transition metal oxide, and an electrochromic material of low molecular weight organic molecule is used. The electrochromic layer is preferably used in a thickness ranging from 10 nm to 10 μm.  
         [0024]     Herein, the electrochromic material of conductive polymer represents not only a polymer having conductivity such as a semiconductor but also a material of which color (absorption spectrum) changes reversibly by applying a voltage. The electrochromic material of conductive polymer includes polyacetylene, polyaniline, polypyrrole, polythiophene, polyphenylenevinylene, and their derivatives, all of which are conjugated polymers linked by conjugated double bonds and conjugated triple bonds. Electrochromism of these electrochromic materials of conductive polymer is based on the following principle. This is explained using polythiophene as an example.  FIG. 4  illustrates the electron resonance structure of polythiophene in its ground state in which two structures, aromatic type structure  21  and quinoid type structure  22 , are possible. Since the aromatic type structure  21  and the quinoid type structure  22  are not energetically equivalent to each other, with the aromatic structure  21  being energetically lower, the ground state of polythiophene is nondegenerate. The resonance of π electrons in polythiophene corresponds to visible wavelength, and therefore, mutually nondegenerate structures are observed in different colors.  
         [0025]     Polyaniline, polypyrrole, polyacetylene, polyphenylenevinylene, and the like in addition to polythiophene are nondegenerate conductive polymers that are similarly nondegenerate in their ground states. It has been reported in Physical Review B, vol. 28, No. 4, pp. 2140-2145 by J. C. Street, et al. that the electrochromism of the nondegenerate conductive polymer can be explained by polaron and bipolaron as described below.  FIG. 5  illustrates changes in the molecular structure of polythiophene associated with doping. When polythiophene in a neutral state  23  is doped with an acceptor, one electron oxidation  24  occurs first to generate one-electron oxidized state  25 . The acceptor used here for the doping includes halogens such as Br 2 , I 2 , and Cl 2 , Lewis acids such as BF 3 , PF 5 , AsF 5 , SbF 5 , SO 3 , BF 4 —, PF 6 —, ASF 6 —, and SbF 6 —, proton acids such as HNO 3 , HCl, H 2 SO 4 , HClO 4 , HF, and CF 3 SO 3 H, halogenated compounds of a transition metal such as FeCl 3 , MoCl 3 , and WCl 5 , and organic substances such as tetracyanoethylene (TCNE) and 7,7,8,8-tetracyanoquinodimethane (TCNQ). The one-electron oxidized state  25  becomes a positively charged polaron state via a relaxation process  26 .  
         [0026]     According to Physics and Chemistry Dictionary, 5th edition ( 1998 , Iwanami Shoten), polaron means a state in which conductive electrons in a crystal move with an associated distortion of the surrounding lattice. Polaron state here is considered by replacing the words in the above definition such that “crystal” corresponds to “neutral state of polythiophene molecule” and “distortion of the surrounding lattice” corresponds to “partial emergence of quinoid structure in polythiophene molecule due to one electron oxidation”. When polythiophene in the polaron state  27  is further doped with an acceptor, oxidation further advances to generate the positive bipolaron state  28 .  
         [0027]     On the other hand, negatively charged polaron and bipolaron are also generated by reduction  29  with donor doping (right side of  FIG. 5 ). The donor used here for the doping includes alkali metals such as Li, Na, K, and Cs and quaternary ammonium ions such as tetraethylammonium and tetrabutylammonium. Both polaron and bipolaron move on the polymer chain, thereby contributing to electric current. In addition to the above dopants, it is also possible to use a polymer electrolyte called polymer dopant. For example, polystyrenesulfonic acid, polyvinylsulfonic acid, and sulfonated polybutadiene are available. When polyaniline, polythiophene, and polypyrrole are produced by polymerization in the presence of these polymer electrolytes, the generated conductive polymers are obtained as ion complexes with the polymer electrolytes used. The use of the polymer dopant is effective for improving fabricability, for example, solubilization of conductive polymer that is insoluble in a solvent.  
         [0028]     The relationship between polaron/bipolaron and electrochromism can be explained by  FIG. 6  in which the electronic state of the nondegenerate conductive polymer is represented by the band structure. The change in electronic state associated with acceptor doping is shown here. In the band structure in the neutral state without doping  32  (see  FIG. 6A ), there is a difference in energy  36  of an electron between the bottom of the valence band  33  and the top of the conduction band  34  that is called the forbidden bandwidth  35 , and a light of energy corresponding to the forbidden bandwidth  35  is absorbed as an allowed transition  37 . When the wavelength of light to be absorbed is in the visible region, it is viewable in color. The forbidden bandwidth  35  of nondegenerate conductive polymer generally ranges from 0.1 eV to 3 eV which is similar to inorganic semiconductors.  
         [0029]     In the band structure of the positive polaron state  38  (see  FIG. 6B ) resulted from doping with the acceptor, two polaron levels, bipolaron level P +   39  and bipolaron level P −   40 , are generated between the valence band  33  and the conduction band  34 , and the allowed transition in the polaron state  41  differs from the allowed transition in the neutral state  37 ; therefore light absorption characteristic changes and the change in the visible region is observed as a change of color. In the band structure of the bipolarlon state  42  in which doping has further proceeded (see  FIG. 6C ), two bipolaron levels, bipolaron level BP +   43  and bipolaron level BP −   44 , are newly generated between the valence band  33  and the conduction band  34 , and the allowed transition in the bipolaron state  45  changes further. Therefore, light absorption characteristics also changes further. Also in doping of a nondegenerate conductive polymer with a donor, a similar change in the behavior of the allowed transition that is caused by a change of the band structure associated with the generation of polaron levels and bipolaron levels is observed as the electrochromism.  
         [0030]     Since the electrochromic properties associated with doping of a nondegenerate conductive polymer are used for the electrochromic device, the nondegenerate conductive polymer here is particularly referred to as an “electrochromic material of conductive polymer”. For the electrochromic material of transition metal oxide, a compound selected from tungsten oxide, iridium oxide, nickel oxide, titanium dioxide, vanadium oxide, and the like is used. As an example, electrochromism of tungsten oxide is explained.  
         [0031]     Tungsten oxide itself is colorless or pale yellow, while its partial reduction makes it reversibly dark blue.  
         [0032]     Electrochromism of tungsten oxide is expressed by Equation 3: 
 
WO 3   +x M +   +xe   −           M x WO 3   (Equation 3) 
 
 where x represents an arbitrary value between 0 and 1, M +  represents a cation such as a proton or lithium ion, and e −  represents an electron. The oxidation-reduction in Equation 3 occurs electrochemically. In the partially reduced state of tungsten oxide shown on the right-hand side of Equation 3, it turns into a “mixed valence state” in which pentavalent tungsten and hexavalent tungsten co-exist, and coloration occurs according to “intervalence transition absorption” due to the transition between tungsten atoms in different valence. Generally, electrochromism of transition metal oxides is closely related to the phenomenon of mixed valence. 
 
         [0033]     The electrolyte layer contains a cation represented by a lithium ion that is necessary for reversible coloration of the electrochromic layer by voltage application and has ionic conductivity. According to the classification of electrolytes based on their phase difference, the liquid electrolyte, gel electrolyte, and solid electrolyte are known, and any one of them can be used. The electrolyte layer is used in a thickness ranging from 50 nm to 5 mm. When a liquid electrolyte or a gel electrolyte is used, the periphery surrounding the electrolyte layer of the device is provided with a spacer or separator. The major components of the electrolyte layer are a lithium salt that serves as a supply source of lithium ion moving reversibly in and out of the electrochromic layer and an organic solvent or polymer material with ionic conductivity that serves as a matrix to dissolve the lithium salt. The ionic conductivity of the electrolyte is preferably from 10 −4  S/cm at around 25 degrees C. It is desired that the material serving as a matrix has no light absorption itself.  
         [0034]     The organic solvents with ionic conductivity include ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, 1,3-dioxolane, dimethylcarbonate, and diethylcarbonate. These solvents can be used either alone or in combination of a plurality of them. Among them, the use of ethylene carbonate or propylene carbonate with excellent ionic conductivity, high boiling point, and low volatility is desirable.  
         [0035]     The polymer materials that can be used include poly(methyl methacrylate) (PMMA), polyvinyl butyral (PVP), poly(ethylene oxide) (PEO), poly(propylene oxide) (PPO), polyacrylonitrile (PAN), poly(vinylidene fluoride) (PVDF), poly(ethylene carbonate) (PEC), and poly(propylene carbonate) (PPC). These polymers can be used either alone or in combination of a plurality of them. Further, these polymer materials can be used as a gel electrolyte in combination with the above organic solvent. For example, although PMMA itself has a property close to an insulator with little conductivity, it can be used as a gel electrolyte when mixed with the above organic solvent with ionic conductivity. The mixing ratio of PMMA to the organic solvent with ionic conductivity in a range of from 1% to 70% by weight is used. Particularly, an excellent ionic conductivity is attained in the range of from 5% to 25%.  
         [0036]     Lithium salts that may be used include lithium tetrafluoroborate (LiBF 4 ), lithium perchlorate (LiClO 4 ), lithium hexafluorophosphate (LiPF 6 ), lithium hexafluoroarsenate (LiAsF 6 ), lithium hexafluoroantimonate (LiSbF 6 ), lithium triflate (LiCF 3 SO 3 ), and N-lithiotrifluoromethanesulfonimide (Li (CF 3 SO 2 ) 2 N). The lithium salt is added to the above organic solvent, polymer material, and mixture of organic solvent and polymer material in a range from 0.1% to 50% by weight.  
         [0000]     Upper Protective Layer  
         [0037]     In addition to the electrochromic layer and electrolyte layer that are layered on the substrate having electrodes, the electrochromic device of the present invention may be used by providing an insulating protective layer on top.  FIG. 26A  is a cross sectional view of an electrochromic device in which an electrolyte layer  474  and an electrochromic layer  475  are laminated in this order on an insulative substrate  471  having a first electrode  472  and a second electrode  473 . An insulating protective layer  476  is provided on the electrochromic layer  475 .  FIG. 26B  is a cross sectional view of an electrochromic device in which the electrochromic layer  475  and the electrolyte layer  474  are laminated in this order on the insulative substrate  471  having a first electrode  472  and the second electrode  473 . An insulating protective layer  476  is provided on the electrolyte layer  474  in this case.  
         [0038]     The insulating protective layer  476  plays a role in preventing damage to the electrochromic layer and the electrolyte layer or preventing penetration of external chemicals that cause deterioration of the electrochromic device. Since the electrochromic reaction is an electrochemical reaction, it is particularly important to prevent penetration of highly reactive water and oxygen. It is necessary for the insulating protective layer to be not only electrically insulative but also mechanically robust against damage, and it is also important that the insulating protective layer is transparent. However, when the device is used from the side of the substrate having electrodes, high transparency of the insulating protective layer is not necessarily required in certain circumstances, and the protective layer may play the role of a white reflective plate, for example. Materials that may be used for the insulating protective layer include laminatable polyethylene, a mixed material of polyethylene with cellophane, polypropylene, polycarbonate, polyester, and the like, polystyrene and poly(vinyl alcohol) that can be fabricated by coating, and the like. The thickness of the insulating protective layer is preferably between 500 nm and 2 mm.  FIG. 27  shows the fabrication method of the device shown in  FIG. 26A  in four consecutive steps shown in  FIG. 27A  through  FIG. 27B .  
         [0039]     The principle of operation of the electrochromic device having the first structure ( FIG. 1B ) of the present invention will now be explained using  FIG. 7 . A device with the use of an electrochromic compound that is colorless in its stationary state and deeply colored by doping with lithium ion such as poly(3,4-ethylenedioxythiophene)-polystyrenesulfonic acid complex or tungsten oxide is used as an example. A power source  210  is connected to a first electrode  202  and a second electrode  203  that are formed on an insulative substrate  201 , and a voltage is applied. The applied voltage here is between 2 V and 20 V. At this time, an electric field  208  formed between the two electrodes  202 ,  203  is present in the inside of an electrochromic layer  204  provided so as to make contact with the upper surface of the insulative substrate  201 , the first electrode  202 , and the second electrode  203  and an electrolyte layer  205  laminated on the electrochromic layer  204 . The electric field  208  is formed in the electrolyte layer  205  beyond the electrochromic layer  204  as well, and lithium ion movement  207  occurs in the area where a potential gradient is generated from the electrolyte layer  205  with relatively high potential to the electrochromic layer  204  with lower potential. Coloration  209  takes place in the region with a lithium ion  206  inserted into the electrochromic layer  204 . It is possible to eliminate this coloration  209  reversibly by stopping the voltage application or by applying a voltage opposite in polarity for a short time period.  
         [0040]     Next, the principle of operation of the electrochromic device having the second structure ( FIG. 2 ) of the present invention is explained using  FIG. 8 . This explanation is also given for the device in which the electrochromic compound that is colorless in its stationary state and deeply colored by doping with lithium ion such as poly(3,4-ethylenedioxythiophene)-polystyrenesulfonic acid complex or tungsten oxide is used. A power source  230  is connected to a first electrode  222  and a second electrode  223  that are formed on an insulative substrate  221 , and a voltage is applied. The applied voltage here is between 2 V and 20 V. At this time, an electric field  228  formed between the two electrodes is present in the inside of an electrolyte layer  224  provided so as to make contact with the upper surface of the insulative substrate  221 , the first electrode  222 , and the second electrode  223  and an electrochromic layer  225  laminated on the electrolyte layer. The electric field  228  is formed in the electrochromic layer  225  beyond the electrolyte layer  224  as well, and lithium ion movement  227  occurs in the area where a potential gradient is generated from the electrolyte layer  224  with relatively high potential to the electrochromic layer  225  with lower potential. Coloration  229  takes place in the region with a lithium ion  226  inserted into the electrochromic layer  225 . It is possible to eliminate this coloration  229  reversibly by stopping the voltage application or by applying a voltage opposite in polarity for a short time period.  
         [0041]     Next, the driving method in which a voltage is externally applied to the electrochromic device of the present invention is explained. A constant-voltage method is the one that can be most easily implemented.  FIG. 9  shows the voltage applied to the device and the associated color change over time of the electrochromic layer that is observed on the second electrode  3  when the device shown in  FIG. 1  is driven by constant voltage. This device is colored when the potential of the second electrode  3  against the first electrode  2  is −V (V) and discolored when it is +V (V). When a write pulse  301  for allowing coloration at time T 1  is supplied, the electrochromic layer on the second electrode  3  becomes a colored state  303 . Then, supply of an erase pulse  302  at time T 2  results in a discolored state  304  (non-colored or opposite state). Further, supply of another write pulse  305  at time T 3  gives rise to coloration of the device again. Coloration and decoloration of the device shown in  FIG. 2  can also be carried out by a similar pulse sequence of applied voltage.  
         [0000]     Electrodes In Parallel  
         [0042]     In addition to the structure described above for the device of the present invention in which two electrodes correspond to each other by a one-to-one relation such that the electrochromic layer on one electrode is colored when a voltage is applied between the two mutually insulated electrodes on an insulative substrate, a structure in which one electrode corresponds to a plurality of other electrodes is also possible. In other words, it is possible to carry out coloration of the electrochromic layer on a plurality of electrodes by applying voltage in such a way that three or more electrodes that are electrically insulated from one another are allowed to correspond by a one-to-two or one-to-many relationship. This is explained below using an illustration. This explanation is also given for the device in which the electrochromic compound that is colorless in its stationary state and deeply colored by doping with lithium such as poly(3,4-ethylenedioxythiophene)-polystyrenesulfonic acid complex or tungsten oxide is used.  
         [0043]     As shown in a cross sectional view of a device in  FIG. 30A , the device is fabricated such that a conductive layer  557  consisting of laminated layers of an electrochromic layer  555  and an electrolyte layer  556  is formed on an insulative substrate  551  provided with a first electrode  552 , a second electrode  553 , and a third electrode  554  that are electrically separated from one another. The cathode of a battery  558  is wired to the first electrode  552 , and the anode of the battery  558  is wired to the second electrode  553  and the third electrode  554 . In the middle of the wiring between the anode of the battery  558  and the second electrode  553  and the third electrode  554 , switches  560  and  559  are connected, respectively.  
         [0044]     In this device, the second electrode  553  and the third electrode  554  can be regarded as being arranged in parallel with respect to the first electrode  552 .  FIG. 30B  illustrates the device viewed from above, where a conductive layer  572  consisting of laminated layers of the electrochromic layer and the electrolyte layer is formed on an insulative substrate  571  provided with a first electrode  573 , a second electrode  574 , and a third electrode  575  that are electrically separated from one another. The cathode of a battery  576  is wired to the first electrode  573 , and the anode of the battery  576  is wired to the second electrode  574  and the third electrode  575 . In the middle of the wiring between the anode of the battery  576  and the second electrode  574  and the third electrode  575 , switches  577  and  578  are connected, respectively. In the illustrated state, the switches  577  and  578  are open, and therefore, no coloration occurs.  
         [0045]     Next, shifting switches  588  and  589  to a closed state forms an electric circuit in which a second electrode  583  and a third electrode  584  are arranged in parallel with respect to a first electrode  582  as shown in a cross sectional view of the device in  FIG. 31A . At this time, an electric field  593  is generated between the first electrode  582  and the second electrode  583  and the third electrode  584 , and movement ( 595 ) of a lithium ion  594  serving as a dopant to an electrochromic layer  586  occurs in areas where potential gradient extends across the interface between an electrolyte layer  585  and the electrochromic layer  586 , giving rise to colored portions  591  and  592 . It is possible to repeat coloration and decoloration for these colored portions  591  and  592  by opening and closing the switches. Since the opening and closing of the switches  588  and  589  can be carried out independently, the portions on the two electrodes can thus be arbitrarily colored.  
         [0046]      FIG. 31B  illustrates the device shown in  FIG. 31A  viewed from above. In the state that switches  607  and  608  are closed, portions  609  and  610  on a second electrode  604  and a third electrode  605  can be observed as colored portions on a conductive layer  602  consisting of laminated layers of the electrochromic layer and the electrolyte layer. It is theoretically possible to provide additional electrodes in parallel that can be independently switched on and off according to these same principles.  
         [0047]     Likewise, in a structure in which the lamination order of the electrochromic layer and the electrolyte layer is opposite to that of the structure shown in  FIG. 30A , it is possible to drive electrodes having a structure in which one electrode corresponds to a plurality of electrodes for parallel coloration and decoloration as shown in  FIG. 33A . In this structure, a first electrode  632  is connected to the anode of a power source  638  by wiring, and a second electrode  633  and a third electrode  634  are connected to the cathode by wiring via switches  639  and  640 , respectively.  FIG. 33B  illustrates this device viewed from above a protective layer  641 .  
         [0048]      FIG. 34A  and  FIG. 34B  are a cross sectional view and a top view of the device when the switches  639  and  640  in  FIG. 33A  were put in closed states ( 669 ,  670 ) and coloration was conducted by applying a voltage ( 668 ) between respective electrodes. Although the principle of coloration of the electrochromic layer  666  on a second electrode  663  and a third electrode  664  is the same as that explained using  FIG. 8 , voltage application results in generating an electric field  674  from two anodes toward one cathode because the electrodes here correspond by one-to-two. The arrows in  FIG. 34A  indicate the direction from lower to higher potential. The colored portions  671 ,  672  can be returned to a discolored state by making the switches open or by applying a voltage opposite to that for coloration while the switches are kept closed, and coloration and decoloration can be repeated reversibly.  
         [0049]     It is also possible to use the device of the present invention for displays that display information by arranging it in a matrix form as a two-dimensional pixel array.  FIG. 10  shows a static driving method in which each pixel is independently controlled. Each pixel  321  is individually wired to a power source  322 , and switching between display and non-display can be carried out by opening and closing a switch  323  to control the voltage applied to the pixel. A matrix driving method in which control of voltage application is carried out by wiring electrodes mutually is also usable for pixel arrangement.  FIG. 11  is an example of image-information display that makes use of a thin-film semiconductor device. A thin silicon film is formed on a substrate  453 . Circuits are packed thereon including a pixel driver area  454 , a buffer amplifier  455 , a gate driver areas  456 , and these work integrally together to function by being connected to an image-information display panel  451  provided with pixels  452 .  
         [0050]      FIG. 12  is a block diagram of a module to arbitrarily drive an array of the electrochromic device of the present invention such as the display shown in  FIG. 11  by using a computer. A command to drive the device is issued from CPU  332  of a control computer  331  and is transmitted from a display controller  334  connected to an image information memory  335  to a display  341 . The command transmitted to the display  341  is executed to drive an electrochromic device array  340  via a driver IC  338  that is composed of a timing controller  336  and a driver  337  including a pixel driver, a gate driver, and similar components. Other components may exist in the display side ( 339 ) and the computer side ( 333 ).  
         [0051]     An electrochromic device having the first structure and an electrochromic device having the second structure according to the present invention will now be compared. The first structure is a structure suitable when a metal oxide type electrochromic material such as tungsten oxide with which an electrochromic layer is formed by a vacuum process such as vapor deposition method or sputtering method, phthalocyanine, porphyrin, and the like are used for the electrochromic material. This is principally based on two reasons. First, the fabrication of a film by the vapor deposition method or the sputtering method requires a mechanical strength for its substrate, and therefore cannot be performed on a liquid electrolyte layer or a gel electrolyte layer. Secondly, when the fabrication of a film is carried out on a solid electrolyte layer by the vapor deposition method or the sputtering method, the surface of the solid electrolyte is modified and deteriorated.  
         [0052]     The second structure is suitable when the fabrication of an electrochromic layer and an electrolyte layer are carried out by a printing method or a coating method. When the electrolyte layer was fabricated on a substrate provided with electrodes, an excellent electrical contact can be achieved. Moreover, the second structure is especially convenient when a soluble electrochromic material such as a complex of polythiophene with polystyrenesulfonic acid is used.  
         [0053]     The use of a plastic substrate such as PET for the display of the present invention is also suitable for use in a bendable sheet display, electronic paper, and similar orientations. Although the transparent background may be used as it is fabricated, it is also possible to use the background by further attaching a backlight such as white LED to the display. For example, a display suitable for electronic paper is made by allowing a white electrolyte layer to be formed by mixing white pigment particles into an electrolyte layer.  
         [0054]     Comparison with Other Display Formats  
         [0055]     The display with the use of the electrochromic device is a non-light-emitting type display and is compared here with other non-light-emitting type displays. First, when compared with liquid crystal, the use of the electrochromic device of the present invention does not require a polarization plate, and therefore, efficiency of light use is high, and a bright display can be produced. In addition, there is a problem in liquid crystal that it has a narrow viewing angle or its brightness significantly differs depending on viewing angles. In the case of the electrochromic device, there is theoretically no dependency on viewing angles. Furthermore, rubbing of a substrate to orient liquid crystal molecules toward a specific direction is needed for liquid crystal, while there is no need of rubbing for the electrochromic device.  
         [0056]     Furhter, in order to allow the substrate to be bent by the use of plastic as well as the display to be fabricated by a simple and low-cost printing process from now on, the electrochromic device is advantageous. Still further, fabrication in a wholly solid state is easier with the electrochromic device than with liquid crystal. The pixel size of a liquid crystal display is generally about 0.3 mm, and it is possible to form high-definition pixels with the electrochromic device that are equal to or of a higher definition than a liquid crystal display.  
         [0057]     As for electronic paper, a microcapsule-type electrophoresis method is known. In this method, black (carbon black) and white (titanium dioxide) particles that are charged negatively and positively, respectively, are sealed into microcapsules, and color viewed from the obverse side is changed by allowing the particles to collect to the front side or the bottom side by means of applying an external electric field. The diameter of a particle is about 40 μm and the resolution of images depends upon the particle diameter. The advantages of the electrochromic device lie in that its cost is low because of no need for preparing special microcapsules, it can be more readily fabricated by coating or printing on electrodes compared with a display fabricated by the microcapsule electrophoresis method, and that the thickness of the whole device can be reduced because the thickness of the electrode layer can be made even thinner than 1 μm.  
         [0058]     According to the above constitutions, the electrochromic device and the electrochromic display can be provided in a simple structure with high transmittance, which addresses the limitations of prior electrochromic and non-electrochromic display devices. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0059]     For the present invention to be clearly understood and readily practiced, the present invention will be described in conjunction with the following figures, wherein like reference characters designate the same or similar elements, which figures are incorporated into and constitute a part of the specification, wherein:  
         [0060]      FIG. 1  shows two cross sectional views of an electrochromic device according to the present invention ( FIG. 1A  and  FIG. 1B );  
         [0061]      FIG. 2  is a cross sectional view of another electrochromic device according to the present invention;  
         [0062]      FIG. 3  is a top view of the electrochromic device of the present invention;  
         [0063]      FIG. 4  shows isomeric structures of polythiophene;  
         [0064]      FIG. 5  is a diagram explaining the principle of electrochromism of polythiophene;  
         [0065]      FIG. 6  is a diagram explaining polaron and bipolaron of a conductive polymer with the use of electron bands in three states ( FIGS. 6A, 6B  and  6 C);  
         [0066]      FIG. 7  is a diagram explaining the principle of operation of the electrochromic device of the present invention;  
         [0067]      FIG. 8  is a diagram explaining another principle of operation of the electrochromic device of the present invention;  
         [0068]      FIG. 9  depicts the transmittance change over time associated with the voltage applied to the electrochromic device of the present invention;  
         [0069]      FIG. 10  is a diagram to show an example of a display with the use of an electrochromic device;  
         [0070]      FIG. 11  is a diagram to show another example of the display with the use of an electrochromic device;  
         [0071]      FIG. 12  is a block diagram of a driving circuit of the display with the use of an electrochromic device;  
         [0072]      FIG. 13  is a structural diagram of a known example of an electrochromic device;  
         [0073]      FIG. 14  illustrates a fabrication method of the electrochromic device of an embodiment of the present invention in four steps ( FIG. 14A  through  FIG. 14D );  
         [0074]      FIG. 15  is a schematic diagram of an electrochromic device;  
         [0075]      FIG. 16  is a top view of an electrochromic device;  
         [0076]      FIG. 17  depicts a visible transmittance spectrum of an electrochromic device;  
         [0077]      FIG. 18  illustrates coloration response associated with voltage application to an electrochromic device;  
         [0078]      FIG. 19  depicts transmittance spectra in a decoloration state of the electrochromic device and an electrochromic device of a comparative example;  
         [0079]      FIG. 20  is a schematic diagram of an electrochromic device of another embodiment of the present invention;  
         [0080]      FIG. 21  is a plan view at the time of coloration viewed from above an electrochromic device;  
         [0081]      FIG. 22  depicts a visible transmittance spectrum of an electrochromic device;  
         [0082]      FIG. 23  illustrates coloration response associated with voltage application to an electrochromic device;  
         [0083]      FIG. 24  illustrates a structure of an information display panel with the use of the electrochromic device of the present invention;  
         [0084]      FIG. 25  illustrates a structure of an information display with the use of the electrochromic device of the present invention;  
         [0085]      FIG. 26  shows two cross sectional views of still another electrochromic device according to the present invention ( FIG. 26A  and  FIG. 26B );  
         [0086]      FIG. 27  illustrates a fabrication method of the electrochromic device of  FIG. 26 , including four sequential processing steps ( FIGS. 27A, 27B ,  27 C, and  27 D);  
         [0087]      FIG. 28  depicts an electrochromic device in cross sectional view ( FIG. 28A ) and a top view ( FIG. 28B );  
         [0088]      FIG. 29  illustrates another fabrication method of the electrochromic device of the embodiment of the present invention in four steps ( FIG. 29A  through  FIG. 29D );  
         [0089]      FIG. 30  depicts an electrochromic device in cross sectional view ( FIG. 30A ) and a top view ( FIG. 30B );  
         [0090]      FIG. 31  depicts an electrochromic device in cross sectional view ( FIG. 31A ) and a top view ( FIG. 31B );  
         [0091]      FIG. 32  is a cross sectional view of the electrochromic device of another embodiment of the present invention;  
         [0092]      FIG. 33  depicts an electrochromic device in cross sectional view ( FIG. 33A ) and a top view ( FIG. 33B );  
         [0093]      FIG. 34  depicts an electrochromic device in cross sectional view ( FIG. 34A ) and a top view ( FIG. 34B );  
         [0094]      FIG. 35  is another cross sectional view of an electrochromic device; and  
         [0095]      FIG. 36  shows a comparison of degree of deterioration between the display device of the present invention and a display device in the prior art. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
     First Exemplary Embodiment  
       [0096]     The Device and Operation  
         [0097]     The fabrication method of an electrochromic device according to the present invention will now be explained.  FIG. 14  illustrates the fabrication method of a device having the first structure using a first method. Part of a 3 cm square insulative glass substrate  361  with 1 mm thickness ( FIG. 14A ) is masked to form thereon two ITO electrodes  363  and  364  with a width of 5 mm and a thickness of 50 nm by magnetron sputtering ( FIG. 14B ). The electric resistance of the formed electrodes is 30 Ω/sq. Thereafter, an electrochromic layer  366  ( FIG. 14C ) with a thickness of 50 nm is formed on the substrate surface with the formed electrodes by spin coating a 5% by weight aqueous solution of a complex of poly(3,4-ethylenedioxythiophene)-polystyrenesulfonic acid for 60 sec at 4,300 rpm. A solution composed of 20% by weight of poly(ethylene oxide) with a molecular weight of 1×10 6 , 2% by weight of lithium perchlorate, and 78% by weight of tetrahydrofuran is applied onto the electrochromic layer  366  by spin coating for 60 sec at 1,000 rpm to form an electrolyte layer  368  in a thickness of 1 μm, and thus, an electrochromic device was fabricated ( FIG. 14D ).  
         [0098]      FIG. 15  is a schematic view of the fabricated electrochromic device after connecting a power source  376  to the electrodes  372 ,  373 .  FIG. 15  shows the electrochromic layer,  375  and the electrolyte layer  374  formed on substrate  371 .  
         [0099]      FIG. 16  is a top view of the fabricated device viewed from above the electrolyte layer. When a voltage of 6 V (from  385 ) is applied to a first ITO electrode  381  with a second ITO electrode  382  as the reference side between the first ITO electrode  381  and the second ITO electrode  382 , the portion where the electrochromic layer and the electrolyte layer were laminated on the first ITO electrode  381  could be observed as a blue-colored portion  386 .  
         [0100]      FIG. 17  depicts the absorption spectrum in a colorless state  391  at the center of the colored portion  386  in  FIG. 16 , and the absorption spectrum in its colored state  392  caused by application of 6 V.  FIG. 18  depicts the change over time of transmittance at 650 nm of the electrochromic layer associated with the voltage application at the center of the colored portion  386  in  FIG. 16 . During the application of +6 V, the transmittance decreased up to 30%, while the colored portion became colorless during −6 V application. The time required for the response of coloration and decoloration was one second. When coloration and decoloration were repeated every one second, it was possible to repeat 100,000 times. The effect of the display of the present invention is not limited to the improvement in transmittance.  
         [0101]      FIG. 36  shows comparison between the display device used in the display of the present invention and a conventional display device shown in  FIG. 13 , where an absolute value of the difference in transmittance (transmittance-modulation value) between when colored by applying 5 V and when discolored by applying −1 V was normalized to each initial value (2nd value) of repeated coloration (this is called an initial value) and where the transmittance-modulation values after repeating coloration 1,000 times  802  were compared to the initial values  801 , respectively. There was no deterioration in the display device used in the display of the present invention even after repeating coloration 1,000 times, whereas there was significant deterioration in the display device in the past invention, resulting in that the transmittance-modulation value decreased to 10% relative to the initial value.  
         [0000]     Electrochromic Materials  
         [0102]     When complexes of poly(3,4-ethylenedioxypyrrole) and poly(3-hexylpyrrole) with polystylenesulfonic acid respectively were used for the electrochromic material of conductive polymer for use in the electrochromic layer, the operation of the device could also be verified. However, polythiophene and its derivatives are better for the electrochromic material of conductive polymer in view of the fact that these are not only more susceptible to doping with a donor represented by Li + , but also excellent in stability to oxidation under a neutral condition. Similar operation could also be achieved with the electrochromic device that utilized polythiophene, poly(3,4-propylenedioxythiophene), poly(3,4-dimethoxythiophene), poly(3-hexylthiophene), or poly(3,3-diethyl-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepin) in place of poly(3,4-ethylenedioxythiophene). Especially when poly(3,4-propylenedioxythiophene) and poly(3,3-diethyl-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepin) were used, the transmittance decreased up to 10% at a wavelength of 580 nm and a high contrast was attained. Further, when the electrochromic layer was formed of tungsten oxide in a thickness of 50 nm by magnetron sputtering, an electrochromic device in which the transmittance changed from 80% to 10% at a wavelength of 580 nm could be fabricated.  
         [0000]     Electrolyte Materials  
         [0103]     Similar operation could also be achieved with the electrochromic device that utilized poly(ethylene oxide), poly(propylene oxide), copolymer of ethylene oxide and epichlorohydrin (70:30), poly(propylene carbonate), or polysiloxane in place of poly(ethylene oxide) as the polymer used for the electrolyte layer. When lithium tetrafluoroborate, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium hexafluoroantimonate, lithium triflate, or N-lithiotrifluoromethanesulfonimide was used as lithium salt for use in the electrolyte layer in place of lithium perchlorate, similar operation could also be achieved.  
       COMPARATIVE EXAMPLE 1  
       [0104]     As a comparative example for the first embodiment of the present invention, a device having a conventional structure was fabricated using the same materials as those in the first embodiment. On two pieces of 3 cm square glass substrates in 1 mm thickness, ITO electrodes in a thickness of 50 nm were formed by magnetron sputtering on their whole surfaces, respectively. The electric resistance of the formed electrodes was 30 Ω/sq. Then, an electrochromic layer in a thickness of 50 nm was formed on the ITO electrode of one piece of the substrate by spin coating a 5% by weight aqueous solution of a complex of poly(3,4-ethylenedioxythiophene)-polystyrenesulfonic acid for 60 sec at 4300 rpm. A solution composed of 20% by weight of poly(ethylene oxide) with a molecular weight of 1×10 6 , 2% by weight of lithium perchlorate, and 78% by weight of tetrahydrofuran was applied onto the electrochromic layer by spin coating for 60 sec at 1,000 rpm to form an electrolyte layer in a thickness of 1 μm, and thus an electrochromic device was fabricated. Onto the electrolyte layer was then attached by laminating the ITO side of the other piece of the glass substrate with ITO electrode to fabricate an electrochromic device having a structure in which the electrochromic layer and the electrolyte layer were sandwiched between a pair of the ITO layers.  
         [0105]     When a voltage of −5 V was applied to the electrode on the electrochromic layer side using the ITO electrode on the electrolyte layer side as the reference between a pair of the ITO electrodes with the use of a power source, the whole electrochromic layer changed to a dark blue color, and thus its operation was confirmed. The coloration was returned to the original colorless state in 5 minutes after the application of the voltage was stopped.  
         [0106]     The visible transmittance spectrum of light penetrating the electrochromic device at its center through the glass substrate, the ITO electrode, the electrochromic layer, the electrolyte layer, the ITO electrode, and the glass substrate in a colorless state of the device is shown by  393  in  FIG. 19 . On the other hand, the visible transmittance spectrum of light penetrating the device fabricated in the first embodiment through the glass substrate, the first electrode, the electrochromic layer, and the electrolyte layer is shown by  394  in  FIG. 19 . The transmittance at a wavelength of 500 nm for the two devices is shown Table 1. Since the device of the present invention has one fewer electrode layer, its overall transmittance was shown to be higher.  
                           TABLE 1                                       Transmittance at           Electrochromic device   wavelength 550 nm (%)                           First embodiment   88%           Comparative example 1   77%                      
 
       Second Exemplary Embodiment  
       [0000]     The Device and Operation  
         [0107]     In the second embodiment, materials identical to those in the first embodiment were used. The fabrication of an electrochromic device having the second structure is explained. Part of a 3 cm square insulative glass substrate with 1 mm thickness was masked to form thereon two ITO electrodes with a width of 5 mm and a thickness of 50 nm by magnetron sputtering. The electric resistance of the formed electrodes was 30 Ω/sq. Then, an electrolyte layer with 1 μm thickness was formed on the substrate surface with the formed electrodes by spin coating a solution composed of 20% by weight of poly(ethylene oxide) with a molecular weight of 1×10 6 , 2% by weight of lithium perchlorate, and 78% by weight of tetrahydrofuran for 60 sec at 1,000 rpm. Subsequently, an electrochromic layer with 50 nm thickness was formed on the electrolyte layer by spin coating a 5% by weight aqueous solution of a complex of poly(3,4-ethylenedioxythiophene)-polystyrenesulfonic acid for 60 sec at 4,300 rpm, and an electrochromic device was fabricated.  
         [0108]      FIG. 20  is a schematic view of the fabricated electrochromic device after connecting a power source  376  to the electrodes  372 ,  373 .  FIG. 20  shows the electrochromic layer,  375  and the electrolyte layer  374  formed on substrate  371 .  
         [0109]      FIG. 21  is a top view of the fabricated device viewed from above the electrolyte layer. When a voltage of 6 V (from 415) was applied to a first ITO electrode  411  with a second ITO electrode  412  as the reference side between the first ITO electrode  411  and the second ITO electrode  412 , the portion where the electrochromic layer and the electrolyte layer were laminated on the second ITO electrode  412  could be observed as a blue-colored portion  416 .  
         [0110]      FIG. 22  depicts the absorption spectrum in a colorless state  421  at the center of the colored portion  416  in  FIG. 21  and the absorption spectrum in its colored state  422  caused by the application of 6 V.  FIG. 23  depicts the change over time of transmittance of the electrochromic layer at a wavelength of 650 nm associated with the voltage application at the center of the colored portion  416  in  FIG. 21 . During the application of +6 V, the transmittance decreased up to 30%, while the colored portion became colorless during −6 V application. The time required for the response of coloration and decoloration was one second.  
         [0000]     Electrochromic Materials  
         [0111]     When complexes of poly(3,4-ethylenedioxypyrrole) and poly(3-hexylpyrrole) with polystyrenesulfonic acid respectively were used for the electrochromic material of conductive polymer for use in the electrochromic layer, the operation of the device could also be verified. However, polythiophene and its derivatives are better for the electrochromic material of conductive polymer in view of the fact that these are not only more susceptible to doping with a donor represented by Li + , but also excellent in stability to oxidation under a neutral condition. Similar operation could also be achieved with the electrochromic device that utilized polythiophene, poly(3,4-propylenedioxythiophene), poly(3,4-dimethoxythiophene), poly(3-hexylthiophene), or poly(3,3-diethyl-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepin) in place of poly(3,4-ethylenedioxythiophene). Especially when poly(3,4-propylenedioxythiophene) or poly(3,3-diethyl-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepin) was used, the transmittance decreased up to 10% at a wavelength of 580 nm, and a high contrast was attained.  
         [0000]     Electrolyte Material  
         [0112]     Similar operation could also be achieved with the electrochromic device that utilized poly(ethylene oxide), poly(propylene oxide), copolymer of ethylene oxide and epichlorohydrin (70:30), poly(propylene carbonate), or polysiloxane in place of poly(methyl methacrylate) as the polymer used for the electrolyte layer. When lithium tetrafluoroborate, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium hexafluoroantimonate, lithium triflate, or N-lithiotrifluoromethanesulfonimide was used as lithium salt for use in the electrolyte layer in place of lithium perchlorate, similar operation could also be achieved.  
       Third Exemplary Embodiment  
       [0113]     An electrochromic device having the first structure of the present invention was fabricated in the same manner as that in the first embodiment except that tungsten oxide was used for the electrochromic compound and that n RF magnetron sputtering method was used to form the electrochromic layer. When a voltage was applied between the electrodes after connecting a power source to this device as in the first embodiment, reversible coloration resulted. Similarly when the device was fabricated using iridium oxide, nickel oxide, titanium dioxide, or vanadium oxide for the electrochromic compound, reversible coloration also resulted.  
       Fourth Exemplary Embodiment  
       [0114]     The fourth embodiment relates to a device arrangement panel on which the electrochromic devices of the present invention were arrayed in a matrix form as pixels on an information display. A matrix display panel and device using 12 pieces of the electrochromic devices shown in  FIGS. 24 and 25  were fabricated by the following method. The materials used were the same as those in the first embodiment.  FIG. 24  illustrates the structure of the display panel, and  FIG. 25  illustrates the structure of the information display. A thin silicon film is formed on a substrate  463 . On the thin silicon film, circuits are packed including a pixel driver area  464 , a buffer amplifier  465 , gate driver areas  466 , and similar structures, and these work integrally together to function by being connected to an image-information display panel  461  provided with pixels  462 .  
         [0115]     The fabrication method of the display panel is as follows. Signal wires  439  and gate wires  440  were prepared on a glass substrate. Twelve pairs of the combination of a first electrode  432  and a second electrode  433  were fabricated by sputtering ITO on the substrate using a mask. The thickness of the electrodes was 50 nm. The size of the first electrode  432  was 9 mm long and 5 mm wide, and the size of the second electrode was 9 mm long and 1 mm wide. The two electrodes were arranged in parallel in the longitudinal direction, and the spacing between the two electrodes was 1 mm. The first electrode was used as a pixel. Next, an electrochromic layer with 100 nm thickness and an electrolyte layer with 500 nm thickness were fabricated by a printing method each in a size of 9 mm long and 9 mm wide at the illustrated place so as to be aligned. Thus, a panel  441  consisting of an array of 12 pieces of the electrochromic devices  431 , transistors for driving the pixels  435 , and wiring was obtained.  
         [0116]     On this panel  441 , image information display could be performed by controlling transistors  435  that apply voltage to allow electrochromic coloration and decoloration using a gate driver  438  and a signal driver  437  according to image information signal input  436 .  
       Fifth Exemplary Embodiment  
       [0117]     The present embodiment relates to an electrochromic device with the use of a liquid electrolyte. The substrate, electrodes, and electrochromic materials used were the same as those in the first embodiment. The electrolyte used was 0.1 M lithium triflate solution in propylene carbonate.  FIG. 28A  is a cross sectional view of the device of the present embodiment. An electrochromic layer  504  was provided on an insulative substrate  501  having a first electrode  502  and a second electrode  503 . A liquid electrolyte  506  was injected into a space surrounded by a glass insulative substrate  505  having a peripheral separator and the electrochromic layer  504 , followed by sealing  507  with an adhesive.  
         [0118]      FIG. 28B  is a top view of the device shown in  FIG. 28A . A voltage was applied between a first electrode  502  and a second electrode  503  with the use of a power source  517 . The first insulative substrate  501  was a square with 4 cm sides, and its thickness was 0.5 mm. The first electrode  502  and the second electrode were both 5 mm wide and 30 nm thick, respectively, with a spacing of 4 mm therebetween, and their sheet resistance was 50 Ω. The second insulative substrate  505  that supported the liquid electrolyte was formed of a glass plate of 3 cm×6 cm in 8 mm thickness of which central portion was hollowed out at a depth of 6 mm leaving its peripheral 5 mm intact, followed by cutting the longitudinal side wall down by 1 mm in order to mount the other first insulative substrate  501 . The thickness of the electrochromic layer  504  was 80 nm.  
         [0119]      FIG. 29  illustrates the fabrication method of the device shown in  FIG. 28  using cross sectional views. To a second insulative substrate  531  ( FIG. 29A ) with formed separator was fixed by adhesion a first insulative substrate  532  on which an electrochromic layer  535 , a first electrode  533 , and a second electrode  534  had already been fabricated ( FIG. 29B ). Then, a liquid electrolyte  536  was injected ( FIG. 29C ), and sealing  537  was formed by sealing the device with a UV-curing transparent resin ( FIG. 29D ).  
         [0120]     When a voltage of 6 V ( 517 ) was applied to the second electrode  503  with the first electrode  502  being made positive, the portion of the electrochromic layer overlapping the second electrode changed to dark blue color in 0.1 second ( 516 ). At this time, the transmittance at a wavelength of 600 nm decreased by 40%. When the voltage application was stopped, the color of the colored portion returned to the original transparent state in 10 seconds. Further, when a voltage of −2 V was applied at the time of decoloration, decoloration occurred in 0.2 second. Even after repeating coloration and decoloration 100,000 times, coloration and decoloration same as those in the initial state could be achieved.  
       Sixth Exemplary Embodiment  
       [0121]     The fabrication method of a parallel type electrochromic device having a cross sectional structure shown in  FIG. 32  in which four electrodes of the electrochromic device on the anode side were arranged against one electrode of the electrochromic device on its cathode side of a battery that was used as a power source is explained.  
         [0122]     Although the device was fabricated according to the fabrication process for the device having the first structure as shown in  FIG. 14 , the number of electrodes differs.  
         [0123]     Part of a 5 cm square insulative glass substrate  611  in 1 mm thickness was masked to form thereon five ITO electrodes  612 - 616  having a width of 5 mm and a thickness of 50 nm with a spacing of 3 mm therebetween by magnetron sputtering. Each electric resistance of the formed electrodes was 30 Ω/sq. Then, an electrochromic layer  617  with a thickness of 60 nm was formed on the substrate surface  616  with the formed electrodes  612 - 616  by spin coating a 5% by weight aqueous solution of a complex of poly(3,4-ethylenedioxythiophene)-polystyrenesulfonic acid for 60 sec at 4,000 rpm. A solution composed of 20% by weight of poly(ethylene oxide) with a molecular weight of 5×10 5 , 2% by weight of lithium perchlorate, and 78% by weight of 1,4-dioxane was applied onto the electrochromic layer  617  by spin coating for 60 sec at 1,000 rpm to form an electrolyte layer  618  in a thickness of 0.5 μm. On top of this layer, a polycarbonate cover layer  628  (thickness, 1 μm) was formed by laminating, and thus the electrochromic device was fabricated.  
         [0124]     The battery ( 620 ) cathode was connected to a first electrode  612 , and the battery anode was connected to a second electrode  613 , a third electrode  614 , a fourth electrode  615 , and a fifth electrode  616  in parallel where switches  621 - 624  located midway of the respective wiring from the battery anode were provided. When a voltage of 6 V was applied from the battery  620  with these switches closed except a switch  622 , portions on the second electrode  613 , the fourth electrode  615 , and the fifth electrode  616  were colored in dark blue. Decoloration and coloration of the colored portions  625 ,  626 , and  627  could be repeated by opening and closing their corresponding switches, respectively. Even when the applied voltage was switched between 6 V and −2 V with a variable-voltage DC power source in stead of switching on and off, coloration and decoloration could also be carried out repeatedly. The decoloration by applying the negative voltage was faster than that by opening the switches. The response time required for the coloration and decoloration was one second, and when coloration and decoloration were repeated every one second, it was possible to repeat 100,000 times.  
         [0125]     The absorption spectra of the colored portions were the same as the spectrum in the colored state  392  in  FIG. 17  because the electrochromic material was the same as that in the first embodiment.  
         [0000]     Electrochromic Materials  
         [0126]     When complexes of poly(3,4-ethylenedioxypyrrole) and poly(3-hexylpyrrole) with polystyrenesulfonic acid respectively were used for the electrochromic material of conductive polymer for use in the electrochromic layer, their operation could also be verified. However, polythiophene and its derivatives are better for the electrochromic material of conductive polymer in view of the fact that these are not only more susceptible to doping with a donor represented by Li + , but also excellent in stability to oxidation under a neutral condition. Similar operation could also be achieved with the electrochromic device that utilized polythiophene, poly(3,4-propylenedioxythiophene), poly(3,4-dimethoxythiophene), poly(3-hexylthiophene), or poly(3,3-diethyl-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepin) in place of poly(3,4-ethylenedioxythiophene). Especially when poly(3,4-propylenedioxythiophene) or poly(3,3-diethyl-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepin) was used, the transmittance decreased up to 10% at a wavelength of 580 nm, and a high contrast was attained. When the electrochromic layer was formed with tungsten oxide in a thickness of 50 nm by magnetron sputtering, an electrochromic device in which the transmittance at a wavelength of 580 nm changed from 80% to 10% could be fabricated.  
         [0000]     Electrolyte Materials  
         [0127]     Similar operation could also be achieved with the electrochromic device that utilized poly(ethylene oxide), poly(propylene oxide), copolymer of ethylene oxide and epichlorohydrin (70:30), poly(propylene carbonate), or polysiloxane in place of poly(methyl methacrylate) as the polymer used for the electrolyte layer. When lithium tetrafluoroborate, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium hexafluoroantimonate, lithium triflate, or N-lithiotrifluoromethanesulfonimide was used as lithium salt for use in the electrolyte layer in place of lithium perchlorate, similar operation could also be achieved.  
       Seventh Exemplary Embodiment  
       [0128]     An electrochromic device of the present invention was also fabricated in the same manner as that in the sixth embodiment except that tungsten oxide was used for the electrochromic compound and that RF magnetron sputtering method was used to form the electrochromic layer. When a voltage was applied between the electrodes after connecting a power source to this device as in the first embodiment, reversible coloration was achieved. Similarly when the device was fabricated using iridium oxide, nickel oxide, titanium dioxide, or vanadium oxide for the electrochromic compound, reversible coloration was also achieved.  
       Eighth Exemplary Embodiment  
       [0129]     In the present embodiment, the fabrication of an electrochromic device having a structure in which the order of laminating the electrochromic layer and the electrolyte layer was reversed compared to that in the sixth embodiment is explained. The insulative substrate, electrodes, electrochromic material, and electrolyte material used were the same as those in the sixth embodiment, respectively. Referencing  FIG. 34A , a cover layer  673  formed of poly(ethylene terephthalate) (PET) in 0.5 mm thickness was formed an electrochromic layer  666  by spin coating (rotations 3,000 rpm, 40 sec). Electrodes on the substrate were also fabricated in the same manner as that in the sixth embodiment. An electrolyte layer  665  in a thickness of 0.3 μm was formed on the surface of the substrate  661  with the formed electrodes by spin coating (rotations 1,200 rpm, 90 sec), followed by laminating with and adhesion to the cover layer with the formed electrochromic layer. Then, a power source  668  and electrodes were wired through switches to provide the electrochromic device shown in  FIG. 34A .  
         [0130]     When a voltage of 6 V was applied in a state that a switch  669  and another switch  670  were closed, portions of the electrochromic layer  666  above a second electrode  663  and a third electrode  664  were colored. Decoloration and coloration of the colored portions could be independently repeated by opening and closing the two switches, respectively. When the applied voltage was switched between 6 V and −2 V with a variable-voltage DC power source in stead of switching on and off, coloration and decoloration could also be carried out repeatedly. The decoloration by applying the negative voltage was faster than that by opening the switch. The response time required for the coloration and decoloration was one second, and when coloration and decoloration were repeated every one second, it was possible to repeat 100,000 times. The absorption spectra of the colored portions were the same as the spectrum in the colored state  392  in  FIG. 17  because the electrochromic material was the same as that in the first embodiment. Furthermore, it was also possible to drive switches using a TFT device.  
       Ninth Exemplary Embodiment  
       [0131]     An electrochromic device of the present invention was fabricated in the same manner as that in the eighth embodiment except that tungsten oxide was used for the electrochromic compound and that RF magnetron sputtering method was used to form the electrochromic layer. When a voltage was applied between electrodes after connecting a power source to this device as in the first embodiment, reversible coloration was possible. Similarly, even when the device was fabricated using iridium oxide, nickel oxide, titanium dioxide, and vanadium oxide for the electrochromic compound, reversible coloration was possible.  
         [0132]     Nothing in the above description is meant to limit the present invention to any specific materials, geometry, or orientation of elements. Many part/orientation substitutions are contemplated within the scope of the present invention and will be apparent to those skilled in the art. The embodiments described herein were presented by way of example only and should not be used to limit the scope of the invention.  
         [0133]     Although the invention has been described in terms of particular embodiments in an application, one of ordinary skill in the art, in light of the teachings herein, can generate additional embodiments and modifications without departing from the spirit of, or exceeding the scope of, the claimed invention. Accordingly, it is understood that the drawings and the descriptions herein are proffered only to facilitate comprehension of the invention and should not be construed to limit the scope thereof.