Electric lamp and discharge devices: systems – Plural power supplies – Plural cathode and/or anode load device
Reexamination Certificate
2000-02-24
2002-04-02
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Plural power supplies
Plural cathode and/or anode load device
C315S169100, C313S498000, C313S500000, C345S076000, C345S077000, C345S092000
Reexamination Certificate
active
06366025
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electroluminescence display apparatus comprising an electroluminescence (hereinafter also referred to as EL) element and a thin film transistor (hereinafter referred to as TFT) element.
2. Description of the Related Art
In recent years, the EL display apparatus employing EL elements has attracted attention as being the display apparatus to replace CRTs and LCDs.
Furthermore, research and development have been conducted on display apparatuses having TFTs as the switching elements to drive the EL elements.
FIG. 1
is a top plan view showing a display pixel and periphery in an organic EL display apparatus of the related art,
FIG. 2A
shows a cross-sectional view along line A—A of
FIG. 1
, and
FIG. 2B
shows a cross-sectional view along line B—B of FIG.
1
.
As shown in
FIG. 1
, a display pixel is formed in a region surrounded by gate signal lines
51
and drain signal lines
52
. A first TFT
30
is provided in proximity to an intersection of both signal lines, and a source
13
s
of the TFT
30
serves as a capacitance electrode
55
, which forms a capacitor with a holding capacitance electrode line
54
to be described later, and is connected to a gate
41
of a second TFT
40
. A source
43
s
of the second TFT
40
is connected to an anode
61
of an organic EL element
60
, and a drain
43
d
at the other end is connected to a power source line
53
, which is a current source that is supplied to the organic EL element
60
.
Furthermore, in the proximity of the TFTs, the holding capacitance electrode line
54
is positioned in parallel with the gate signal lines
51
. The holding capacitance electrode line
54
is formed from a material such as chromium, and the capacitance electrode
55
is connected to the source
13
s
of the TFT
30
. The electric charge is stored between the holding capacitance electrode line
54
and the capacitance electrode
55
, via a gate insulating film
12
, thus forming a capacitor. This holding capacitor is provided to hold a voltage that is applied to the gate electrode
41
of the second TFT
40
.
As shown in
FIGS. 2A and 2B
, the organic EL display apparatus is formed by laminating in sequence the TFT and the organic EL element onto a substrate
10
, such as a substrate formed from glass or synthetic resin, a conductive substrate, or a semiconductor substrate. However, when a conductive substrate or a semiconductor substrate is used for the substrate
10
, an insulating film is formed, such as from SiO
2
or SiN, on which the TFT and organic EL display element are formed.
The first TFT
30
, which is a switching TFT, will be described first.
As shown in
FIG. 2A
, gate signal lines
51
also serving as gate electrodes
11
and formed from a refractory metal, such as chromium or molybdenum, and the holding capacitance electrode
54
are formed on the insulating substrate
10
, such as of quartz glass or no-alkali glass. Next, the gate insulating film
12
and an active layer
13
, which is formed from a poly-silicon (p-Si) film, are formed in sequence.
On the entire surface of the gate insulating film
12
, the active layer
13
and stopper insulating films
14
, is formed an interlayer insulating film
15
in which a SiO
2
film, a SiN film, and a SiO
2
film are laminated in sequence. A drain electrode
16
, which is filled with a metal, such as A
1
, is provided at a contact hole formed at a position corresponding to a drain
13
d
of the interlayer insulating film
15
. Furthermore, a planarization insulating film
17
, which is formed from an organic resin, is formed on the entire surface of the substrate so as to planarize the surface.
The second TFT
40
, which is a TFT for driving the organic EL element, will be described next.
As shown in
FIG. 2B
, the gate electrodes
41
, which is formed from a refractory metal, such as Cr or Mo, the gate insulating film
12
, and the active layer
43
which is formed from a p-Si film, are formed in sequence on the insulating substrate
10
which is made of quartz glass or no-alkali glass. In the active layer
43
are provided channels
43
c,
and on both sides of the channels
43
c,
the source
43
s
and the drain
43
d.
On the entire surface of the gate insulating film
12
and the active layer
43
is formed the interlayer insulating film
15
in which a SiO
2
film, a SiN film, and a SiO
2
film are laminated in sequence. A power source line
53
connected to a power source (not shown) and filled with a metal, such as A
1
, is provided at a contact hole formed to correspond to the drain
43
d.
Furthermore, the planarization insulating film
17
, which is formed from an organic resin or the like, is formed on the entire surface so as to planarize the surface. A contact hole is formed at a position corresponding to the source
43
s
of the planarization insulating film
17
and the interlayer insulating film
15
, and a transparent electrode, namely, the anode
61
of the organic EL element, which is formed from ITO (indium tin oxide) and contacting the source
43
s
via this contact hole, is provided on the planarization insulating film
17
.
The organic EL element
60
, provided at each pixel so as to enable light emission at each pixel, has a structure in which are formed in sequence the anode
61
made of a transparent electrode, such as ITO, a hole transport layer
62
having a first hole transport layer formed such as from MTDATA (4,4′,4″-tris(3-methylphenylphenylamino)triphenylamine) and a second hole transport layer formed such as from TPD (N,N′-diphenyl-N,N′-di(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine), an emissive layer
63
formed such as from Bebq
2
(bis(10-hydroxybenzo[h]quinolinato) beryllium) including a Quinacridon derivative, an electron transport layer
64
formed such as from Bebq
2
, and a cathode
66
formed from an alloy, such as magnesium-indium. The hole transport layer
62
, the emissive layer
63
, and the electron layer
64
form an emissive element layer
65
.
In this organic EL element, holes injected from the anode and electrons injected from the cathode recombine, and organic molecules forming the emissive layer are excited and yield exitons. Light is released from the emissive layer in the process where the exitons undergo radiation deactivation, and this light is released to the outside from the transparent anode via the transparent insulating substrate.
However, the emission efficiency of the emissive layer for emitting light of various colors differs with each color.
However, in the EL display apparatus of the related art shown in
FIG. 3
, emissive regions
1
B,
1
R, and
1
G for the display pixel of the respective color are arranged in a matrix configuration at every intersection of a plurality of the gate signal lines
51
and a plurality of the drain signal lines
53
and all have identical emissive areas in size. Thus, in order to obtain the same luminance at the display pixels having a low emission efficiency, a current larger than that supplied to the other display pixels having a high emission efficiency must be supplied. This causes the life of those display pixels having a low emission efficiency, in particular, to shorten, and also possibly causes the life of the EL display apparatus to shorten.
Furthermore, when the emissive areas of the display pixels of various colors, each having a different emission efficiency, are set to be identical, color balance (white balance) is difficult to achieve, and higher currents must be supplied to certain emissive layers to achieve such a balance. Thus, a drawback is that deterioration occurs at the EL elements in the display pixels supplied with the higher currents.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention, which takes into consideration the above-mentioned disadvantage of the related art, to provide a display apparatus having emissive elements, such as EL elements, in which the control of white balance is simple and the service life
Cantor & Colburn LLP
Sanyo Electric Co,. Ltd.
Vo Tuyet T.
Wong Don
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