Display apparatus using electroluminescence elements

A pixel of an organic electroluminescence (EL) display apparatus includes an EL element and an added capacitor connected in parallel with the EL element. The added capacitor provides improved image quality. To further improve image quality, an added resistor may be connected in series with the EL element, and in parallel with the added capacitor. Alternatively, the added resistor may be connected in series with the added capacitor, and in parallel with the EL element. The pixel may be used in both a simple matrix display system or an active matrix display system.

BACKGROUND OF THE INVENTION 
The present invention relates generally to a display apparatus having an 
improved image quality. More particularly, the present invention relates 
to a display apparatus using electroluminescence elements. 
Electroluminescence (EL) elements include an inorganic EL element which 
uses a thin film of an inorganic compound like selenium or zinc as a 
luminous material, and an organic EL element which uses an organic 
compound as a luminous material. The organic EL element preferably has the 
following features: (1) high luminous efficiency, (2) low drive voltage, 
(3) ability to display multifarious colors (green, red, blue, yellow, etc. 
by selection of a luminous material in use, (4) clear display and no need 
for a back light because it is of a self light emission type, (5) planar 
light emission and no dependency on the angle of visibility, (6) thin and 
light weight, and (7) low peak temperature in the fabrication process, 
which allows a soft material like a plastic film to be used for the 
substrate. Because of these properties, a display apparatus using such 
organic EL elements (organic EL display apparatus) has recently been 
getting attention as a replacement for a CRT or LCD. 
An organic EL display apparatus can employ either a simple matrix system or 
an active matrix system. The simple matrix system allows an external drive 
unit to directly drive organic EL elements as a matrix of pixels, arranged 
on a display panel, in synchronism with a scan signal. Because the display 
panel of a display apparatus which employs this system is formed of 
organic EL elements, the drive time (duty) assigned to each pixel becomes 
shorter as the number of scan lines is increased, which lowers the 
contrast of an image displayed on the display panel. 
The active matrix system has pixel driving element (active elements) 
provided respectively, for a matrix of pixels. Each pixel driving element 
serves as a switch which is switched on or off by the scan signal. When a 
pixel driving element is enabled, a data signal (display signal, video 
signal) is transmitted via that pixel driving element to an anode of the 
associated organic EL element and is written there. In this manner, the 
organic EL element is driven. When the pixel driving element is disabled, 
the data signal applied to the anode of the organic EL element is held as 
a charge in the organic EL element. The organic EL element is thus driven 
until the associated pixel driving element is switched on. The drive time 
per pixel becomes shorter as the number of scan lines is increased, 
therefore, the driving of the organic EL elements is not affected. As a 
result, the contrast is not lowered. In this respect, the active matrix 
system displays images with a higher quality than the simple matrix 
system. 
The active matrix system employs transistor type (three-terminal type) 
pixel driving elements or diode type (two-terminal type) pixel driving 
elements. The transistor type is characterized as easily acquiring high 
contrast and high resolution, but is difficult to fabricate, as compared 
with the diode type. That is, the transistor type organic EL display 
apparatus provides high-quality images which match those displayed by a 
CRT. The operational principle of the active matrix system is mainly 
associated with the transistor type pixel driving elements. 
Both the writing characteristic and the holding characteristic required of 
the individual pixels in the simple matrix system and active matrix system 
are important characteristics. The writing characteristic indicates 
whether or not a desired data signal can be written sufficiently in each 
organic EL element within a predetermined unit time conforming to the 
specifications of the display panel. The holding characteristic indicates 
whether or not a data signal, once written in each organic EL element, can 
be held for a predetermined time that conforms to the specifications of 
the display panel. 
When multiple organic EL elements are arranged in a matrix, the size of the 
individual elements is structurally restricted and the electrostatic 
capacitance (hereinafter referred to as "capacitance") of the elements is 
limited. An organic EL element having a smaller capacitance has a lower 
holding characteristic, which makes it difficult to provide a display 
apparatus capable of displaying high-quality images. 
Broadly speaking, the present invention is directed to a display apparatus 
using electroluminescence elements, which is capable of providing 
high-quality and stable display images. The present invention can be 
implemented in numerous ways, including as an apparatus and a method. 
SUMMARY OF THE INVENTION 
Briefly, the present invention is directed to a display apparatus 
comprising electroluminescence (EL) elements and added capacitors 
connected in parallel to the EL elements, respectively. The present 
invention is further directed to a display apparatus comprising a matrix 
of pixels, wherein each pixel includes an EL element and an added 
capacitor connected in parallel to the EL element. 
The present invention further provides a display apparatus of a simple 
matrix system. The apparatus includes a matrix of pixels, each pixel 
including an electroluminescence element having a first electrode, a 
second electrode and a luminous element layer provided between the first 
electrode and the second electrode, an insulator film provided over one of 
the first electrode and the second electrode, and a third electrode 
provided in or over the insulator film so as to face one of the first 
electrode and the second electrode. The one of the first and second 
electrodes, the third electrode and the insulator film form an added 
capacitor. The added capacitor is connected in parallel to the 
electroluminescence element. 
The present invention also provides a display apparatus of an active matrix 
system. The apparatus comprising a matrix of pixels and driving elements 
for driving the matrix of pixels, respectively. Each pixel including an 
electroluminescence element having a first electrode, a second electrode 
and a luminous element layer provided between the first electrode and the 
second electrode, an insulator film provided over one of the first 
electrode and the second electrode, a third electrode provided in or over 
the insulator film so as to face one of the first electrode and the second 
electrode. The one of the first and second electrodes, the third electrode 
and the insulator film forms an added capacitor. The added capacitor is 
connected in parallel to the electroluminescence element.

Other aspects and advantages of the invention will become apparent from the 
following description, taken in conjunction with the accompanying 
drawings, illustrating by way of example the principles of the invention. 
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention is directed to an organic EL display apparatus and to 
a pixel thereof. The invention may be used for a simple matrix display 
system and an active matrix display system, as discussed below. In the 
drawing, like numerals are used to reference like elements. 
First Embodiment 
An organic EL display apparatus according to a first embodiment of the 
present invention will now be described referring to the accompanying 
drawings. FIG. 1 is a schematic cross-sectional view of one pixel in an 
organic EL display apparatus using a simple matrix system according to the 
first embodiment. A pixel 1 includes an insulator substrate 2, an 
electrode 3 located on the insulator substrate 2, a transparent insulator 
film 4 provided on the insulator substrate 2 and the electrode 3, an anode 
5 placed on the insulator film 4, a hole transporting layer 6 provided on 
the anode 5, a luminous layer 7 formed on the hole transporting layer 6, 
an electron transporting layer 8 formed on the luminous layer 7, and a 
cathode 9 provided on the electron transporting layer 8. 
The transparent insulator substrate 2 is preferably a transparent insulator 
formed of glass or synthetic resin. The insulator film 4 is also 
preferably transparent and is preferably formed of silicon nitride, 
silicon oxide or silicon nitride oxide. The electrode 3 and anode 5 are 
preferably transparent electrodes formed of ITO (Indium Tin Oxide) or the 
like. The individual layers 6 to 8, which are preferably formed of organic 
compounds, form a luminous element layer. Further, the individual layers 6 
to 8, the anode 5 and the cathode 9 form an organic EL element 10. The 
hole transporting layer 6 in the organic EL element 10 may be omitted in 
which case two layers of the luminous layer 7 and the electron 
transporting layer 8 form an organic compound layer. The hole transporting 
layer 6 comprises a first hole transporting layer and a second hole 
transporting layer. This structure provides the organic EL element 10 
which has a very high luminous efficiency. That is, the luminance of the 
organic EL display apparatus is improved. 
The color of light emitted by the organic EL element 10 can be changed by 
the selection of materials for the organic compound that forms the 
luminous layer 7. For example, Bebq2(10-benzo[h]quinolinol-beryllium 
complex) may used for the emission of green light, OXD (oxadiazole) or AZM 
(azomethine-zinc complex) may be used for the emission of blue light, PYR 
(pyrazoline) may be used for the emission of blue green light, 
Znq2(8-quinolinol-zinc complex) may be used for the emission of yellow 
light, and ZnPr(porphyrin-zinc complex) may be used for the emission of 
red light. The use of such organic EL elements which have different 
luminous colors provides a color display apparatus. 
A passivation film (not shown) may be placed on the transparent insulator 
film 4 to cover the organic EL element 10. The pixels 1 are arranged in a 
matrix form to provide a display panel of the organic EL display 
apparatus. 
The electrode 3 and anode 5 are arranged on both surfaces of the 
transparent insulator film 4 so that they face each other, with the 
transparent insulator film 4 in between. The transparent insulator film 4 
serves as a dielectric film. The transparent insulator film 4, the 
electrode 3 and the anode 5 form a capacitor or added capacitor (auxiliary 
capacitor) 11. The anode 5 serves as the first electrode of the added 
capacitor 11, while the electrode 3 serves as the second electrode of the 
added capacitor 11. 
The anode 5 is electrically connected to the positive terminal of a drive 
power supply 12, and the electrode 3 and the cathode 9 are electrically 
connected to the negative terminal of the drive power supply 12. The 
organic EL element 10 and the added capacitor 11 are selectively connected 
in parallel to the drive power supply 12 via a switch (not shown). 
In the organic EL element 10, holes (not shown) are injected into the 
luminous layer 7 from the anode 5, and electrons are injected into the 
luminous layer 7 from the cathode 9. Then, the holes are combined with the 
electrons in the luminous layer 7. As a result, light is emitted from the 
luminous layer 7. The emitted light is sent outside, passing through the 
anode 5, the transparent insulator film 4, the electrode 3 and the 
transparent insulator substrate 2. The hole transporting layer 6 
facilitates the injection of holes from the anode 5 and block electrons 
from the cathode 9. The electron transporting layer 8 facilitates the 
injection of electrons from the cathode 9. 
According to the first embodiment, since the organic EL element 10 and the 
added capacitor 11 are connected in parallel to the drive power supply 12, 
the holding characteristic of the pixel 1 is improved by the capacitance 
of the added capacitor 11. That is, the added capacitor 11 supplements the 
organic EL element 10 with capacitance. The organic EL element 10 and the 
added capacitor 11 can be used to implement an organic EL display 
apparatus of a simple matrix system which provides high-quality images. 
Suppose that a silicon oxide film (a dielectric constant .di-elect cons. of 
3.8 and a specific dielectric constant .di-elect cons.0 of 8.85 
.times.10.sup.-14) is used for the transparent insulator film 4, the film 
thickness d of the transparent insulator film 4 between the electrode 3 
and the anode 5 is set to 1000 .ANG., and the electrode 3, anode 5 and 
cathode 9 are formed into a rectangular shape with a size of 50.times.150 
.mu.m. In this case, the added capacitor 11 has a capacitance C of 2.5 pF. 
When the voltage of the drive power supply 12 is 6 V, a charge of 15 pC is 
stored in the added capacitor 11. 
It is assumed that each pixel 1 is designed to maintain light emission for 
about 0.1 msec, according to a specification of the display panel. Then, a 
current I of 0.15 .mu.A flows through the added capacitor 11 and the 
organic EL element 10. Therefore, a current of 2.0 mA/cm.sup.2 per unit 
area flows through the anode 5 and the cathode 9 of the organic EL element 
10. This current allows the pixel 1 or the organic EL element 10 to 
maintain a luminance of over 100 cd/m.sup.2, even if the drive time (duty) 
assigned to each pixel decreases, such as about 60% of the drive time, as 
the number of scan lines is increased. The added capacitor 11 can 
therefore improve the holding characteristic of the pixel 1 and enable the 
pixel 1 to sufficiently hold the luminance for the required time. 
Second Embodiment 
A display apparatus according to a second embodiment of the present 
invention will now be described referring to the accompanying drawings. 
FIG. 2 is a schematic cross-sectional view of one pixel 21 in an organic EL 
display apparatus of an active matrix system according to the second 
embodiment. 
The pixel 21 includes an organic EL element 10, an added capacitor 11, and 
an added resistor 22. A thin film transistor (TFT) 23 is provided as a 
pixel driving element. A passivation film (not shown) is placed on a 
transparent insulator film 4 to cover the added resistor 22, the organic 
EL element 10 and the TFT 23. 
It is preferable that the added resistor 22 comprises a high-resistance 
film formed on the cathode 9 of the organic EL element 10. An amorphous 
silicon film, polycide film or a silicide film may be used as the 
high-resistance film. 
The TFT 23 is preferably a planar type, and is preferably formed into an 
LDD (Lightly Doped Drain) structure by using a polycrystalline silicon 
film 24 as an active layer. The TFT 23 may comprise a TFT having an SD 
(Single Drain) structure or a double gate structure. Further, the TFT 23 
may further comprise a TFT of a reversed planar type, a staggered type or 
a reverse staggered type. A TFT which uses amorphous silicon film as an 
active layer may be used as well. 
The polycrystalline silicon film 24 is located on the transparent insulator 
film 4. A gate insulator film 25 is provided on the polycrystalline 
silicon film 24, with a gate electrode 26 formed on the gate insulator 
film 25. Defined on the polycrystalline silicon film 24 are a high-density 
drain region 27a, a low-density drain region 27b, high-density source 
region 28a and a low-density source region 28b. A drain electrode 29 is 
provided on the high-density drain region 27a. 
The anode 5 of the organic EL element 10 is formed to extend along the 
surface of the transparent insulator film 4 so that it is connected to the 
high-density source region 28a. The anode 5 thus serves as the source 
electrode of the TFT 23. 
FIG. 3 is a schematic design of an organic EL display apparatus 31 
according to the second embodiment. The organic EL display apparatus 31 
includes a display panel 201, a gate driver 202, and a drain driver (data 
driver) 203. 
The display panel 201 has a plurality of gate lines (scan lines) G1, . . . 
, Gn, Gn+1, . . . , and Gm, and a plurality of drain lines (data lines) 
D1, . . . , Dn, Dn+1, . . . , and Dm. The drain lines are preferably laid 
substantially perpendicular to the gate lines. Pixels 21 are provided at 
the intersections of the gate lines G1-Gm and the drain lines D1-Dm. 
The gate driver 202 is connected to the gate lines G1-Gm and applies a gate 
signal (scan signal) to the gate lines G1-Gm. The drain driver 203 is 
connected to the drain lines D1-Dm and applies a data signal thereto. The 
drivers 202 and 203 form a peripheral drive circuit 204. Each of the gate 
lines G1-Gm is formed by the gate electrode 26 of the TFT 23. Each of the 
drain lines D1-Dm is formed by the drain electrode 29 of the TFT 23. In 
the TFT 23, the drain regions 27a and 27b may serve as a source region, 
the drain electrode 29 may serve as a source electrode, and the source 
regions 28a and 28b may serve as a drain region. In this case, the drain 
lines D1-Dm serve as source lines, while the drain driver 203 serves as a 
source driver. 
FIG. 4 shows an equivalent circuit of the pixel 21 located at the 
intersection of the gate line Gn and the drain line Dn. The organic EL 
element 10 is connected to a common cathode line CL via the added resistor 
22. The common cathode line CL, which is common to all of the pixels 21, 
is formed by the electrode 3 of the added capacitor 11. A substantially 
constant voltage is applied to the common cathode line CL. 
The organic EL element 10 and the added resistor 22, connected in series to 
each other, and the added capacitor 11 are connected in parallel between 
the source region 28a of the TFT 23 and the common cathode line CL. 
E According to the second embodiment, when a positive voltage is applied to 
the gate line Gn, thus applying a positive voltage to the gate electrode 
26 of the TFT 23, the TFT 23 is turned on. Consequently, the electrostatic 
capacitor of the organic EL element 10 and the added capacitor 11 are 
charged with the data signal applied to the drain line Dn, causing the 
data signal to be written in the pixel 21. The organic EL element 10 is 
thus driven by data signal. 
When a negative voltage is applied to the gate line Gn, thus applying a 
negative voltage to the gate electrode 26 of the TFT 23, the TFT 23 is 
turned off. Then, the electrostatic capacitor of the organic EL element 10 
and the added capacitor 11 hold the data signal applied to the drain line 
Dn in the form of charges. In this manner, an arbitrary data signal is 
held in each pixel 21. The driving of the organic EL element 10 continues 
until the TFT 23 is turned on again. 
According to the second embodiment, even if the drive time assigned to each 
pixel 21 becomes shorter with an increase in the number of gate lines 
(scan lines), the driving of the organic EL element 10 is not affected, 
which prevents the contrast of an image to be displayed on the display 
panel 201 from getting deteriorated. The organic EL display apparatus 31 
of the active matrix system according to the second embodiment thus 
provides high-quality display images. 
The series circuit of the organic EL element 10 and added resistor 22, and 
the added capacitor 11 are connected in parallel between the TFT 23 and 
the common cathode line CL, which allows the capacitance of the added 
capacitor 11 to improve the holding characteristic of each pixel 21. The 
organic EL display apparatus 31 may be used as an active matrix system 
which displays high-quality images. 
The added resistor 22 is provided to supplement the internal resistance of 
organic EL element 10. If the organic EL element 10 has a small internal 
resistance and the added resistor 22 is not provided, a time constant of 
the internal resistance of the organic EL element 10 and the capacitance 
of the added capacitor 11 decreases. The decreased time constant shortens 
the data-signal holding time of the pixel 21, thus deteriorating the 
holding characteristic. The added resistor 22 is provided to overcome such 
a shortcoming. According to the second embodiment, assuming that the 
conditions for the transparent insulator film 4, the electrode 3, the 
anode 5 and the cathode 9 are set as in the first embodiment and the 
current I flowing through the added capacitor 11 is set to 0.15 .mu.A, it 
is preferable to set the resistance of the added resistor 22 to about 40 
M.OMEGA.. The added resistor 22 may also be used with the pixel 1 of the 
first embodiment. 
Since the pixel 21 in the second embodiment includes the TFT 23, the pixel 
21 occupies a relatively large area on the display panel. The use of a TFT 
23 having a relatively small transistor size can avoid an increase in the 
area of the TFT 23 as much as possible, while sufficiently driving the 
pixel 21. Suppose that the width (gate width W) and the length (gate 
length) of the gate electrode 26 of the TFT 23 are both set to about 5 
.mu.m. Then, a current of about 10 to about 20 .mu.A flows between the 
source and drain. This current value is sufficiently larger than the value 
of the current I (0.15 .mu.A) that flows through the added capacitor 11 
and the organic EL element 10, which permits the use of the TFT 23 having 
a small transistor size. 
The TFT 23 of the LDD structure, which uses the polycrystalline silicon 
film 24 as an active layer, has a large ON/OFF ratio and permits a small 
leak current to flow when it is off. This can ensure the display of a 
high-quality image. 
Third Embodiment 
A display apparatus according to a third embodiment of the present 
invention will be described below with reference to the accompanying 
drawings. 
FIG. 5 is a schematic cross-sectional view of one pixel 41 in an organic EL 
display apparatus of a simple matrix system according to the third 
embodiment. The pixel 41 includes a transparent insulator substrate 2, an 
anode 5, a hole transporting layer 6, a luminous layer 7, an electron 
transporting layer 8, a cathode 9, an insulator film 42, and an electrode 
43. The individual components 5 to 9, 42 and 43 are laminated on the 
transparent insulator substrate 2 in the order shown in FIG. 5. 
The insulator film 42 is preferably formed of silicon nitride, silicon 
oxide or silicon nitride oxide. The insulator film 42 need not be 
transparent, and may be formed using known insulative materials which have 
the desired insulation property. 
The electrode 43 is preferably formed of an aluminum alloy film, a 
high-melting-point metal film, a high-melting-point metal compound film, a 
silicide film, a polycide film or a doped polysilicon film. The electrode 
43 need not be transparent, and may be formed of a film which has a low 
resistance. 
The electrode 43 and the cathode 9 are arranged to face each other with the 
insulator film 42 in between. The insulator film 42 serves as a dielectric 
film. The insulator film 42, the electrode 43 and the cathode 9 form a 
capacitor or an added capacitor 44. The cathode 9 serves as the first 
electrode of the added capacitor 44, while the electrode 43 serves as the 
second electrode of the added capacitor 44. 
The electrode 43 and the anode 5 are connected to the positive terminal of 
a drive power supply 12, and the cathode 9 to the negative terminal of the 
drive power supply 12. Thus, the organic EL element 10 and the added 
capacitor 44 are selectively connected in parallel to the drive power 
supply 12 via a switch (not shown). 
As the organic EL element 10 and the added capacitor 44 are connected in 
parallel to the drive power supply 12 according to the third embodiment, 
the holding characteristic of the pixel 41 is improved by the capacitance 
of the added capacitor 44. That is, the added capacitor 44 supplements the 
organic EL element 10 with the capacitance. The pixel 41 may be used to 
implement a high image-quality organic EL display apparatus. 
Fourth Embodiment 
A display apparatus according to a fourth embodiment of the present 
invention will be described below with reference to the accompanying 
drawings. To avoid a redundant description, like or same reference 
numerals are given to those components that are like or the same as the 
corresponding components of the first to third embodiments. FIG. 6 is a 
schematic cross-sectional view of one pixel 51 in an organic EL display 
apparatus of an active matrix system. 
The pixel 51 includes an organic EL element 10, an added capacitor 44 and 
an electrode 52. A TFT 23 is provided as a pixel driving element. Provided 
on a transparent insulator substrate 2 are the organic EL element 10 and 
an insulator film 53 whose surfaces are flattened. That is, the insulator 
film 53 eliminates a step formed on the transparent insulator substrate 2 
by the organic EL element 10. The insulator film 53 is preferably formed 
of silicon nitride, silicon oxide or silicon nitrogen oxide. The insulator 
film 53 need not be transparent, and may be formed of a material which has 
a predetermined desired insulation property. 
The organic EL element 10 comprises a cathode 9, an electron transporting 
layer 8, a luminous layer 7, a hole transporting layer 6 and an anode 5 as 
an added resistor, which are laminated on the transparent insulator 
substrate 2 in the named order. The anode 5 is preferably formed of a 
high-resistance film which is preferably a polycide film or a silicide 
film. 
The electrode 52 is located on the anode 5 of the organic EL element 10. 
The electrode 52 is formed to extend along a surface of the insulator film 
53, and is connected to a high-density source region, 28a, of the TFT 23. 
The electrode 52 thus serves as the source electrode of the TFT 23. 
Provided on the electrode 52 is an insulator film 42 on which an electrode 
43 is located. The electrodes 52 and 43 are arranged to face each other 
with the insulator film 42 in between. The insulator film 42 serves as a 
dielectric film. The insulator film 42, the electrode 52 and the electrode 
43 form a capacitor or an added capacitor 44. The electrode 52 serves as 
the first electrode of the added capacitor 44, and the electrode 43 serves 
as the second electrode of the added capacitor 44. As the added capacitor 
44 and the anode 5 are connected together, the anode 5 and the electrode 
52 also serve as the first electrode of the added capacitor 44. 
FIG. 7 is a schematic diagram of an organic EL display apparatus 54 
according to the fourth embodiment. The organic EL display apparatus 54 
includes a display panel 201, a gate driver 202, and a drain driver 203. 
FIG. 8 shows an equivalent circuit of the pixel 51 located at the 
intersection of the gate line Gn and the drain line Dn. The organic EL 
element 10 is connected to a common cathode line CL. The common cathode 
line CL, which is common to all of the pixels 51, is formed by the cathode 
9 of the organic EL element 10. Therefore, the series circuit of the 
organic EL element 10 and the anode 5, and the added capacitor 44 are 
connected in parallel between the high-density source region 28a and the 
common cathode line CL. 
The fourth embodiment uses the TFTs 23, as per the second embodiment, to 
prevent the contrast from being degraded and to ensure a high-quality 
display image. The series circuit of the organic EL element 10 and anode 
5, and the added capacitor 44 are connected in parallel between the TFT 23 
and the common cathode line CL. This circuit permits the holding 
characteristic of each pixel 51 to be improved by the capacitance of the 
added capacitor 44. The implemented organic EL display apparatus 54 of an 
active matrix system can display high-quality images. 
Fifth Embodiment 
A display apparatus according to a fifth embodiment of the present 
invention will now be described with reference to the accompanying 
drawings. 
FIG. 9 is a schematic cross-sectional view of one pixel 55 in an organic EL 
display apparatus of an active matrix system according to the fifth 
embodiment. The pixel 55 includes an organic EL element 10, an added 
capacitor 57 and an added resistor 58. A TFT 60 is provided as a pixel 
driving element. 
An electrode 56, a transparent insulator film 59, the added resistor 58 and 
the organic EL element 10 are preferably laminated on a transparent 
insulator substrate 2 in the named order. The transparent insulator film 
59 is preferably formed of silicon nitride, silicon oxide or silicon 
nitride oxide. The electrode 56 and the added resistor 58 are preferably 
transparent electrodes formed of ITO (Indium Tin Oxide) or the like. The 
electrode 56 serves as the first electrode of the added capacitor 
(auxiliary capacitor) 57. It is preferable that the added resistor 58 is a 
high-resistance film formed of amorphous silicon, polycide or silicide. 
The electrode 56 and the added resistor 58 face each other with the 
transparent insulator film 59 located in between. The transparent 
insulator film 59 thus serves as a dielectric film. Further, the 
transparent insulator film 59, the electrode 56 and the added resistor 58 
form a capacitor or the added capacitor 57. 
The TFT 60 is preferably a planar type which has an active layer which is 
comprised of a polycrystalline silicon film 61 (or amorphous silicon 
film). The polycrystalline silicon film 61 is provided on the transparent 
insulator substrate 2. Formed on the polycrystalline silicon film 61 is a 
gate insulator film 62 on which a gate electrode 63 is provided. A drain 
region 64 and a source region 65 are defined on the polycrystalline 
silicon film 61. The drain region 64 is connected to a drain electrode 66. 
In the TFT 60, the drain region 64 may serve as a source region, the drain 
electrode 66 may serve as a source electrode, and the source region 65 may 
serve as a drain region. 
The added resistor 58 preferably extends along a surface of the transparent 
insulator film 59 and is connected to the source region 65 of the TFT 60. 
The anode 5 of the organic EL element 10 serves as the source electrode of 
the TFT 60. An insulator film 67 is formed on the TFT 60 to eliminate the 
step of the organic EL element 10. A passivation film 68 is formed on the 
organic EL element 10 and the insulator film 67. 
FIG. 10 is an equivalent circuit diagram of the pixel 55. The organic EL 
element 10 is connected between the drain line (positive terminal of the 
drive power supply) Dn and a common cathode line CL via the TFT 60. The 
added resistor 58 is connected via the added capacitor 57 to the common 
cathode line CL. That is, the series circuit of the added resistor 58 and 
added capacitor 57, and the organic EL element 10 are connected in 
parallel between the source region 65 of the TFT 60 and the common cathode 
line CL. Therefore, the holding characteristic of each pixel 55 is 
improved by the capacitance of the added capacitor 57. The pixel 55 may be 
used to implement an organic EL display apparatus of an active matrix 
system which displays high-quality images. The organic EL display 
apparatus of an active matrix system according to the fifth embodiment, 
like the second embodiment, uses the TFTs 60 and is thus able to display 
high-quality images. Further, the added resistor 58 is provided in 
parallel to the organic EL element 10 in the fifth embodiment. This 
particular arrangement of the added resistor 58 prevents a writing 
characteristic of the pixel 55 from being degraded by the added resistor 
58. 
Sixth Embodiment 
A display apparatus according to a sixth embodiment of the present 
invention will now be described with reference to the accompanying 
drawings. FIG. 11 is a schematic cross-sectional view of one pixel 70 in 
an organic EL display apparatus of an active matrix system according to 
the sixth embodiment. 
The pixel 70 includes an organic EL element 10 and an added capacitor 72. A 
TFT 60 is provided as a pixel driving element. An electrode 71, a 
transparent insulator film 59, an electrode 73 and the organic EL element 
10 are preferably laminated on a transparent insulator substrate 2 in the 
named order. The electrode 71 functions as an added resistor. It is 
preferable that the electrode 71 is a high-resistance film formed of an 
amorphous silicon, polycide or silicide. The electrode 71 also serves as 
the first electrode of the added capacitor (auxiliary capacitor) 72, and 
the electrode 73 as the second electrode of the added capacitor 72. 
The electrodes 71 and 73 face each other with the transparent insulator 
film 59 located in between. The transparent insulator film 59 thus serves 
as a dielectric film. The transparent insulator film 59, the electrode 71 
and the electrode 73 form a capacitor or the added capacitor 72. 
The electrode 73 preferably extends along the surface of the transparent 
insulator film 59 and is connected to the source region 65 of the TFT 60. 
That is, the anode 5 of the organic EL element 10 serves as the source 
electrode of the TFT 60. 
FIG. 12 is an equivalent circuit diagram of the pixel 70. The organic EL 
element 10 is connected between the drain line (positive terminal of the 
drive power supply) Dn and a common cathode line CL via the TFT 60. The 
electrode (added resistor) 71 is connected between the added capacitor 72 
and the common cathode line CL. The series circuit of the added capacitor 
72 and the added resistor 71, and the organic EL element 10 are connected 
in parallel between the source region 65 of the TFT 60 and the common 
cathode line CL. Therefore, the holding characteristic of the pixel 70 is 
improved by the capacitance of the added capacitor 72. The pixel 70 may be 
used to implement an organic EL display apparatus of an active matrix 
system which displays high-quality images. The parallel arrangement of the 
electrode 71 as an added resistor and the organic EL element 10 prevents 
the writing characteristic from being degraded by the electrode 71. 
Further, the organic EL display apparatus according to the sixth 
embodiment ensures a high-quality display by using the TFTs 60, as per the 
second embodiment. 
Seventh Embodiment 
A display apparatus according to a seventh embodiment of the present 
invention will be described below with reference to the accompanying 
drawings. FIG. 13 is a schematic cross-sectional view of one pixel 75 in 
an organic EL display apparatus of an active matrix system according to 
the seventh embodiment. 
Each pixel 75 includes an organic EL element 10 and an added capacitor 72. 
A TFT 60 is provided as a pixel driving element. An electrode 76, which is 
the first electrode of the added capacitor (auxiliary capacitor) 72, 
serves as an added resistor, and preferably extends below the TFT 60 in 
order to block the influence of ions, such as sodium ions or potassium 
ions, contained in glass, on the TFT 60 when low quality glass containing 
such ions is used for a transparent insulator substrate 2. Thus, the pixel 
75 operates stably, which improves the reliability of the pixel 75. The 
remaining structure of the pixel 75 is the same as that of the pixel 70 of 
the sixth embodiment (see FIG. 11). 
Eighth Embodiment 
A display apparatus according to an eighth embodiment of the present 
invention will now be described with reference to the accompanying 
drawings. FIG. 14 is a schematic cross-sectional view of one pixel 80 in 
an organic EL display apparatus of an active matrix system according to 
the eighth embodiment. 
The pixel 80 includes an organic EL element 10, an added capacitor 81 and 
an added resistor 84. A TFT 60 is provided as a pixel driving element. An 
electrode 56, a transparent insulator film 59, the added resistor 84 and 
the organic EL element 10 are preferably laminated on a transparent 
insulator substrate 2 in the named order. The electrode 56 serves as the 
first electrode of the added capacitor (auxiliary capacitor) 81. 
The added resistor 84 preferably comprises an N.sup.+ type polycrystalline 
silicon film 82 located on the transparent insulator film 59, and a 
P.sup.+ type polycrystalline silicon film 83 located on the silicon film 
82. Therefore, the added resistor 84 operates as a variable resistor with 
a PN junction structure. When a current flows in the forward direction to 
the N.sup.+ type polycrystalline silicon film 82 from the P.sup.+ type 
polycrystalline silicon film 83, the added resistor 84 serves as a 
low-resistance resistor. When a current flows in the reverse direction to 
the P.sup.+ type polycrystalline silicon film 83 from the N.sup.+ type 
polycrystalline silicon film 82, the added resistor 84 serves as a 
high-resistance resistor. 
The electrode 56 and the added resistor 84 face each other with the 
transparent insulator film 59 located therebetween. The transparent 
insulator film 59 thus serves as a dielectric film. The transparent 
insulator film 59, the electrode 56 and the added resistor 84 form a 
capacitor or the added capacitor 81. 
The P.sup.+ type polycrystalline silicon film 83 extends along the surface 
of the transparent insulator film 59 and is connected to the source region 
65 of the TFT 60. Since, the anode 5 of the organic EL element 10 is in 
contact with the P.sup.+ type silicon film 83, the anode 5 serves as the 
source electrode of the TFT 60. 
FIG. 15 is equivalent circuit diagram of the pixel 80. The organic EL 
element 10 is connected between the drain line (positive terminal of the 
drive power supply) Dn and a common cathode line CL via the TFT 60. The 
added resistor 84 is connected by way of the added capacitor 81 to the 
common cathode line CL. Therefore, the series circuit of the added 
resistor 84 and added capacitor 81, and the organic EL element 10 are 
connected in parallel between the source region 65 of the TFT 60 and the 
common cathode line CL. 
According to the eighth embodiment, when a positive voltage is applied to 
the gate line Gn, thus applying a positive voltage to the gate electrode 
63 of the TFT 60, the TFT 60 is turned on. Consequently, the electrostatic 
capacitance of the organic EL element 10 and the added capacitor 81 are 
charged with the data signal applied to the drain line Dn, causing the 
data signal to be written in the pixel 80. The organic EL element 10 is 
driven by the data signal. At this time, the added resistor 84 serves as a 
low-resistance resistor, so that the current flows in the forward 
direction to the N.sup.+ type polycrystalline silicon film 82 from the 
P.sup.+ type polycrystalline silicon film 83, quickly charging the added 
capacitor 81. 
When a negative voltage is applied to the gate line Gn, thus applying a 
negative voltage to the gate electrode 63 of the TFT 60, the TFT 60 is 
turned off. Then, the data signal applied to the drain line Dn is held in 
the form of charges by the electrostatic capacitance of the organic EL 
element 10 and the added capacitor 81. In accordance with the light 
emission from the organic EL element 10, the current flows to the organic 
EL element 10 from the added capacitor 81. At this time, the added 
resistor 84 function as a high-resistance resistor, so that the current 
flows in the reverse direction to the P.sup.+ type polycrystalline 
silicon film 83 from the N.sup.+ type polycrystalline silicon film 82, 
slowly discharging the added capacitor 81. The organic EL element 10 is 
kept driven until the TFT 60 is turned on again. 
According to the eighth embodiment, when a data signal is written, the 
added resistor 84 serves as a low-resistance resistor, making the time 
constant smaller, so that the added capacitor 81 is charged promptly. When 
a data signal is held, the added resistor 84 serves as a high-resistance 
resistor, increasing the time constant, which causes the added capacitor 
81 to be discharged slowly. Even if the drive time assigned to a single 
pixel 80 becomes shorter with an increase in the number of gate lines 
(scan lines), the added capacitor 81 is sufficiently charged. Such a 
charging and discharging operation reduces the influence on the drive of 
the organic EL element 10 and prevents the contrast of a display image on 
the display panel decreasing. Thus, the pixel 80 may be used to implement 
an organic EL display apparatus of an active matrix system which displays 
high-quality images. 
Ninth Embodiment 
A display apparatus according to a ninth embodiment of the invention will 
now be described with reference to the accompanying drawings. FIG. 16 is a 
schematic cross-sectional view of one pixel 85 in an organic EL display 
apparatus of an active matrix system according to the ninth embodiment. 
The pixel 85 includes an organic EL element 10, an added resistor 88 and 
an added capacitor 89. A TFT 60 is provided as a pixel driving element. 
The added resistor 88, a transparent insulator film 59, an electrode 73, 
and the organic EL element 10 are preferably laminated on a transparent 
insulator substrate 2 in the named order. The added resistor 88 serves as 
the first electrode of the added capacitor (auxiliary capacitor) 89, and 
the electrode 73 serves as the second electrode of the added capacitor 89. 
The added resistor 88 comprises an N.sup.+ type polycrystalline silicon 
film 86 located on the transparent insulator substrate 2, and a P.sup.+ 
type polycrystalline silicon film 87 located on the silicon film 86. The 
added resistor 88 operates as a variable resistor with a PN junction 
structure. 
The electrode 73 and the added resistor 88 face each other with the 
transparent insulator film 59 located therebetween. The transparent 
insulator film 59 thus serves as a dielectric film. The transparent 
insulator film 59, the electrode 73 and the added resistor 88 form a 
capacitor or the added capacitor 89. 
FIG. 17 is an equivalent circuit design of the pixel 85. The organic EL 
element 10 is connected between the drain line (positive terminal of the 
drive power supply) Dn and a common cathode line CL via the TFT 60. The 
added resistor 88 is connected between the added capacitor 89 and the 
common cathode line CL. That is, the series circuit of the added capacitor 
89 and the added resistor 88, and the organic EL element 10 are connected 
in parallel between the source region 65 of the TFT 60 and the common 
cathode line CL. The holding characteristic of the pixel 85 is improved by 
the capacitance of the added capacitor 89. The pixel 85 may be used to 
implement a high-image-quality, organic EL display apparatus of an active 
matrix system. The use of the added resistor 88, which serves as a 
variable resistor, further improves the holding characteristic of the 
pixel 85 as per the eighth embodiment, which realizes an organic EL 
display apparatus of an active matrix system which displays images with a 
high quality. 
Tenth Embodiment 
A display apparatus according to a tenth embodiment of the present 
invention will be described below with reference to the accompanying 
drawings. FIG. 18 is a schematic cross-sectional view of one pixel 90 in 
an organic EL display apparatus of an active matrix system according to 
the tenth embodiment. 
The pixel 90 includes an organic EL element 10 and an added capacitor 89. A 
TFT 60 is provided as a pixel driving element. In the tenth embodiment, an 
N.sup.+ type polycrystalline silicon film 91 of an added resistor 92 is 
formed to extend below the TFT 60. When low-cost glass is used for a 
transparent insulator substrate 2, therefore, the N.sup.+ type 
polycrystalline silicon film 91 blocks the influence of ions contained in 
the glass, such as sodium ions or potassium ions, on the TFT 60. 
Preventing such ion influence ensures the stable operation of the pixel 
90, thus improving the reliability of the pixel 90. The remaining 
structure of the pixel 90 is the same as that of the pixel 85 of the ninth 
embodiment. 
A preferred method of fabricating the pixel 90 will now be discussed. As 
shown in FIG. 19A, the N.sup.+ type polycrystalline silicon film 91 is 
preferably formed to be about 500 .ANG. thick on the transparent insulator 
substrate 2 of glass. Next, a P.sup.+ type polycrystalline silicon film 
87 having a thickness of about 500 .ANG. is formed in an area on the 
N.sup.+ type polycrystalline silicon film 91 where an added capacitor is 
to be formed. As a result, the added resistor 92 comprised of the N.sup.+ 
type polycrystalline silicon film 91 and P.sup.+ type polycrystalline 
silicon film 87 is formed. 
Then, the transparent insulator film 59 of, for example, silicon oxide is 
formed on the added resistor 92 as shown in FIG. 19B. A polycrystalline 
silicon film 61, which becomes an active layer of the TFT, is formed on 
the transparent insulator film 59. The area where the polycrystalline 
silicon film 61 is formed is different from the area where the P.sup.+ 
type polycrystalline silicon film 87 is formed. A transparent insulator 
film 62 of, for example, silicon oxide is formed on the transparent 
insulator film 59 to cover the polycrystalline silicon film 61. 
Next, a gate electrode 63 is formed on the transparent insulator film 62, 
as shown in FIG. 19C. With the gate electrode 63 as a mask, a 
high-concentration P type impurity is injected in the surface of the 
polycrystalline silicon film 61, which forms a drain region 64 and a 
source region 65. Then, an electrode 73 and a drain electrode 66, both of 
aluminum or ITO, are formed on the transparent insulator film 62. The 
electrode 73 and the source region 65 are connected together by a contact 
hole, and the drain electrode 66 and the drain region 64 are connected by 
another contact hole. The anode 5, the hole transporting layer 6, the 
luminous layer 7 and the electron transporting layer 8 are sequentially 
formed on the electrode 73 in a known manner. 
Next, as shown in FIG. 19D, an insulator film 67 is formed to cover the TFT 
60, and the cathode 9 is formed of ITO on the electron transporting layer 
8. The cathode 9 and the N.sup.+ type polycrystalline silicon film 91 are 
connected together by a contact hole. Then, a passivation film (see FIG. 
18) is formed to cover the cathode 9 of the organic EL element 10 and the 
TFT 60, thus yielding the pixel 90. 
When the concentration of the P type impurity in the P.sup.+ type 
polycrystalline silicon film 87 and the concentration of the N type 
impurity in the N.sup.+ type polycrystalline silicon film 91 are set 
equal to or greater than about 1.times.10.sup.18 /cm.sup.3 in the tenth 
embodiment, the added resistor 92 functions as a Zener diode, which shows 
the reverse characteristic at a voltage Voff of about 5 V, as shown in 
FIG. 21. FIGS. 20A and 20B show an equivalent circuit of the pixel 90 
including a Zener diode 93. 
When the TFT 60 is turned on, the current Ion flows through the organic EL 
element 10 and the added capacitor 89, as shown in FIG. 20A. At this time, 
the Zener diode 93 functions as a low-resistance resistor due to the 
forward bias. The added capacitor 89 is therefore charged. 
When the TFT 60 is turned off, the current Ioff flows toward the organic EL 
element 10 from the added capacitor 89, as shown in FIG. 20B. At this 
time, the Zener diode 93 functions as a high-resistance resistor due to 
the reverse bias. Therefore, the current Ioff is limited to a smaller 
value by the resistance of the Zener diode 93, which allows the light 
emission time of the organic EL element to be maintained for a relatively 
long period of time. 
When the concentration of the P type impurity in the P.sup.+ type 
polycrystalline silicon film 87 and the concentration of the N type 
impurity in the N.sup.+ type polycrystalline silicon film 91 are set 
equal to or greater than approximately 3.times.10.sup.19 /cm.sup.3, the 
added resistor 92 serves as a tunnel diode which has a tunnel effect, as 
shown in FIG. 23. The tunnel diode normally permits the reverse current to 
flow. Such an arrangement of the silicon films, however, causes the 
reverse current to flow when the TFT 60 is turned off. When the added 
resistor 92 functions as a tunnel diode, therefore, the arrangement of the 
silicon films should be reversed. Specifically, in FIG. 18, the P.sup.+ 
type polycrystalline silicon film 87 is formed on the transparent 
insulator substrate 2 first, and an N.sup.+ type polycrystalline silicon 
film is then formed on the P.sup.+ type polycrystalline silicon film 87. 
The P.sup.+ type polycrystalline silicon film is connected to the common 
cathode line CL. FIGS. 22A and 22B show an equivalent circuit of a pixel 
having a tunnel diode 94. 
When the TFT 60 is turned on, the current Ion, which is reverse to the 
tunnel diode 94, flows through the organic EL element 10 and the added 
capacitor 89, as shown in FIG. 22A. When the TFT 60 is turned off, the 
forward current flows to the tunnel diode 94 from the added capacitor 89, 
as shown in FIG. 22B. It is preferable to set the voltage Voff to a value 
corresponding to a middle value between the tunnel current and diffusion 
current, so that a constant forward current flows. This is preferred 
because the organic EL element 10 can be driven by the constant forward 
current. 
Eleventh Embodiment 
A display apparatus according to an eleventh embodiment of the present 
invention will now be described with reference to the accompanying 
drawings. FIG. 24 is a schematic cross-sectional view of one pixel 95 in 
an organic EL display apparatus of an active matrix system according to 
the eleventh embodiment. 
The pixel 95 includes an organic EL element 10, an added capacitor 96 and 
an added resistor 99. A TFT 60 is provided as a pixel driving element. An 
electrode 56, a transparent insulator film 59, the added resistor 99 and 
the organic EL element 10 are preferably laminated on a transparent 
insulator substrate 2 in the named order. The electrode 56 serves as the 
first electrode of the added capacitor (auxiliary capacitor) 96. 
The added resistor 99 comprises a variable resistor, which includes an 
N.sup.+ type polycrystalline silicon film 97 formed on the transparent 
insulator film 59, and a P.sup.+ type polycrystalline silicon film 98 
located on the silicon film 97. The electrode 56 and the added resistor 99 
face each other with the transparent insulator film 59 located 
therebetween. The transparent insulator film 59 thus serves as a 
dielectric film. The transparent insulator film 59, the electrode 56, and 
the added resistor 99 form a capacitor or the added capacitor 96. 
The N.sup.+ type polycrystalline silicon film 97 preferably extends along 
the surface of the transparent insulator film 59 and is connected to the 
source region 65 of the TFT 60. Since, the anode 5 of the organic EL 
element 10 is in contact with the added resistor 99, the anode 5 serves as 
the source electrode of the TFT 60. 
FIG. 25 is an equivalent circuit diagram of the pixel 95. The organic EL 
element 10 is connected via the added resistor 99 to the TFT 60. The added 
capacitor 96 is connected between the TFT 60 and a common cathode line CL. 
As show, the series circuit of the added resistor 99 and the organic EL 
element 10, is connected in parallel to the added capacitor 96, between 
the source region 65 of the TFT 60 and the common cathode line CL. The 
holding characteristic of the pixel 95 is improved by the capacitance of 
the added capacitor 96. The pixel 95 may be used to implements an organic 
EL display apparatus of an active matrix system which has a high image 
quality, while preventing the contrast of an image from getting lower. 
According to the eleventh embodiment, when a positive voltage is applied to 
the gate line Gn, thus applying a positive voltage to the gate electrode 
63 of the TFT 60, the TFT 60 is turned on. Consequently, the electrostatic 
capacitor of the organic EL element 10 and the added capacitor 96 are 
charged with the data signal applied to the drain line Dn, causing the 
data signal to be written in the pixel 95 with the organic EL element 10 
being driven by the data signal. 
When a negative voltage is applied to the gate line Gn, thus applying a 
negative voltage to the gate electrode 63 of the TFT 60, the TFT 60 is 
turned off. Then, the data signal is held in the form of charges by the 
electrostatic capacitor of the organic EL element 10 and the added 
capacitor 96. The organic EL element 10 is kept driven until the TFT 60 is 
turned on again. 
Twelfth Embodiment 
A display apparatus according to a twelfth embodiment of the present 
invention will be described below with reference to the accompanying 
drawing. FIG. 26 is a schematic cross-sectional view of one pixel 100 in 
an organic EL display apparatus of an active matrix system according to 
the twelfth embodiment. 
The pixel 100 includes an organic EL element 10 and an added capacitor 96. 
A TFT 60 is provided as a pixel driving element. In the twelfth 
embodiment, an electrode 101 is formed to extend below the TFT 60. The 
electrode 101 blocks the influence of ions such as sodium ions or 
potassium ions, contained in a transparent insulator substrate 2 made of 
glass, on the TFT 60. Preventing such ion influence ensures the stable 
operation of the pixel 100 and improves the reliability of the pixel 100. 
The remaining structure of the pixel 100 is the same as that of the pixel 
95 of the eleventh embodiment. 
Thirteenth Embodiment 
A display apparatus according to a thirteenth embodiment of the present 
invention will now be described with reference to the accompanying 
drawings. FIG. 27 is a schematic cross-sectional view of one pixel 105 in 
an organic EL display apparatus of an active matrix system according to 
the thirteenth embodiment. 
The pixel 105 includes an organic EL element 10 and an added capacitor 106. 
A TFT 60 is provided as a pixel driving element. An electrode 56, a 
transparent insulator film 59, an electrode 107, the organic EL element 10 
and an added resistor 110 are preferably laminated on a transparent 
insulator substrate 2 in the named order. The electrode 56 serves as the 
first electrode of the added capacitor (auxiliary capacitor) 106, and the 
electrode 107 serves as the second electrode of the added capacitor 106. 
The added resistor 110 includes an N.sup.+ type polycrystalline silicon 
film 108, formed on the cathode 9 of the organic EL element 10, and a 
P.sup.+ type polycrystalline silicon film 109 formed on the silicon film 
108, and operates as a variable resistor. The electrodes 56 and 107 face 
each other with the transparent insulator film 59 located therebetween. 
The transparent insulator film 59 thus serves as a dielectric film. The 
transparent insulator film 59 and the electrodes 56 and 107 form a 
capacitor or the added capacitor 106. 
The electrode 107 extends along the surface of the transparent insulator 
film 59 and is connected to the source region 65 of the TFT 60. Since, the 
anode 5 of the organic EL element 10 is in contact with the electrode 107, 
the anode 5 serves as the source electrode of the TFT 60. 
FIG. 28 is an equivalent circuit diagram of the pixel 105. The organic EL 
element 10 is connected via the added resistor 110 to a common cathode 
line CL. The added capacitor 106 is connected between the TFT 60 and the 
common cathode line CL. Specifically, the series circuit of the organic EL 
element 10 and the added resistor 110 is connected in parallel to the 
added capacitor 106, between the source region 65 of the TFT 60 and the 
common cathode line CL. 
It should be apparent to those skilled in the art that the present 
invention may be embodied in many other specific forms without departing 
from the spirit or scope of the invention. For instance, the present 
invention may be adapted to an organic EL display apparatus which employs 
a transistor type or diode type of an active matrix system that uses bulk 
transistors as pixel driving elements. Diode type pixel driving elements 
include an MIM (Metal Insulator Metal) diode, ZnO (Zinc Oxide) varistor, 
MSI (Metal Semi-Insulator) diode, BTB (Back to Back) diode and RD (Ring 
Diode). The present invention may be adapted to a display apparatus which 
uses inorganic EL elements. Therefore, the present examples and 
embodiments are to be considered as illustrative and not restrictive and 
the invention is not to be limited to the details given herein, but may be 
modified within the scope and equivalence of the appended claims.