Electric lamp and discharge devices: systems – Plural power supplies – Plural cathode and/or anode load device
Reexamination Certificate
1999-11-30
2001-06-12
Philogene, Haissa (Department: 2821)
Electric lamp and discharge devices: systems
Plural power supplies
Plural cathode and/or anode load device
C315S169100, C345S076000, C345S092000, C313S498000, C313S506000
Reexamination Certificate
active
06246179
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a display device using a self-luminous element, and particularly to a display device using an electroluminescence element and a thin-film transistor.
2. Description of the Related Art
In recent years, electroluminescence (referred to hereinafter as “EL”) display devices comprising EL elements are regarded as devices that may replace CRT and LCD. Research has been conducted for the development of EL display devices using, for example, thin film transistors (referred to hereinafter as “TFT”) as switching elements to drive the EL elements.
FIG. 1
shows a plan view of a possible configuration of an active type EL display device, and
FIG. 2
shows a cross-sectional view taken along line II—II of FIG.
1
.
As shown in
FIG. 1
, a TFT is disposed near a junction of a gate signal line
51
with gate electrodes
11
and a drain signal line
52
. The drain of the TFT is connected to the drain signal line
52
, and the gate of the TFT is connected to the gate signal line
51
. Further, the source of the TFT is connected to the anode
81
of an EL element.
As shown in
FIG. 2
, a display pixel
110
is formed by sequentially laminating a TFT and an organic EL element on a substrate
10
which may be a substrate made of glass or synthetic resin, a conductive substrate, or a semiconductor substrate. When a conductive substrate or a semiconductor substrate is used as the substrate
10
, an insulating film made of materials such as SiO
2
or SiN is deposited before the TFT is formed.
Gate electrodes
11
made of refractory metal such as chromium (Cr) are first formed on the insulator substrate
10
. Subsequently, a gate insulating film
12
and an active layer
13
composed of p-Si film are sequentially formed.
In the active layer
13
, channels
13
c
are formed in a position above the gate electrodes
11
. Ion doping is performed using stopper insulating film
14
formed on the channels
13
c
as masks. Regions on both sides of the gate electrodes
11
are then covered with a resist, and further ion doping is conducted. As a result, low-concentration regions
13
LD are disposed on both sides of the channels
13
c
. Furthermore, a source
13
s
and a drain
13
d
, which are high-concentration regions, are formed on the outer sides of the low-concentration regions
13
LD, respectively. The described structure is the so-called LDD (Lightly Doped Drain) structure.
Subsequently, an interlayer insulating film
15
comprising a sequential lamination of a Sio
2
film, a SiN film, and a SiO
2
film is formed to cover the entire region over the gate insulating film
12
, the active layer
13
, and the stopper insulating film
14
. A contact hole formed with respect to the drain
13
d
is filled with metal such as aluminum (Al) to provide the drain electrode
16
. A planarizing insulating film
17
consisting of, for example, organic resin is formed over the entire surface, planarizing the surface. A contact hole is formed in the planarizing insulating film
17
at a location corresponding to the source
13
s
, and an anode
81
of an EL element is then formed over the planarizing insulating film
17
through the contact hole. The anode
81
is composed of ITO (Indium Tin Oxide), and simultaneously serves as the source electrode through its contact with the source
13
s
via the contact hole.
Subsequently, an EL element is formed on the anode
81
.
In the organic EL element, holes injected from the anode
81
and electrons injected from the cathode
87
recombine in the emissive layer which is one layer within the emissive element layer
86
including organic compounds. As a result, organic molecules constituting the emissive layer are excited, generating excitons. Through the process in which these excitons undergo radiation until deactivation, light is emitted from the emissive layer. This light radiates outward through the side of the transparent anode
81
via the transparent insulator substrate
10
, resulting in light emission.
When the EL element is formed as described above, the emissive element layer
86
deposited over the anode
81
is extremely thin, generally at a thickness of approximately less than 2000 Å. The emissive element layer
86
therefore provides poor coverage at uneven portions on the planarizing insulating film
17
at the peripheral portions of the anode
81
(indicated by arrows). The poor coverage may also result at irregularities in the surface created by the TFT through, for example, the thickness of the Al wiring. A problem exists where the emissive element layer
86
becomes disconnected, and the cathode
87
disposed over the emissive element layer and the anode
81
forms a short circuit at the disconnected portion. In such cases, pixels produce deficient displays.
Another existing problem is that an electric field becomes concentrated at the uneven portions created by the thickness of the anode
81
, especially at the edges on the peripheral portions of the anode
81
, thereby speeding up the deterioration of the emissive layer.
A further disadvantage is that some of the emitted light irradiates the TFT underneath the emissive element layer. Because of such light, leakage current of the TFT increases, and stable TFT characteristics and stable display cannot be achieved.
SUMMARY OF THE INVENTION
The present invention was created in light of the above existing disadvantages. The purpose of the present invention is to prevent formation of short circuits between the cathode and the anode due to disconnection in the emissive element caused by the thickness of the anode. Another purpose of the present invention is to provide an EL element and an EL display device which reduces deterioration of the emissive layer due to concentration of electric field at the edges of the anode and which achieves stable display by preventing light from the emissive element layer from reaching the TFT.
The emissive element or the display device of the present invention comprises an emissive region formed by laminating a first electrode, an emissive element layer, and a second electrode. An insulating film is disposed on at least a peripheral portion of the first electrode to separate the first electrode from the emissive element layer and/or the second electrode.
According to another aspect of the present invention, each pixel in the display device is provided with the emissive element. Moreover, the first electrode is separately formed for each pixel, and a peripheral portion of each of the separately formed first electrodes is covered by the insulating film.
In a further aspect of the present invention, the insulating film is disposed between the first electrode and the emissive element layer.
In a different aspect of the present invention, the insulating film overlaps the first electrode along the entire peripheral portion outlining the first electrode.
By providing such insulating film between the first electrode and the emissive element layer and/or the second electrode, it is possible to prevent problems occurring at the uneven portion created by the thickness of the first electrode, such as disconnection of the overlying emissive element layer or the second electrode, and formation of short circuit between the first and the second electrodes. Furthermore, the insulating layer covering the peripheral portion of the first electrode reduces concentration of electric field at this peripheral portion, and thereby reduces characteristics deterioration of the overlying emissive element layer. The effect of reduction in characteristics deterioration is enhanced especially when the entire peripheral portion outlining the first electrode is covered with the insulating film.
According to another aspect of the present invention, the insulating film in the emissive element or the display device covers a peripheral portion of the first electrode, and includes an opening over the associated first electrode. An edge portion of the opening forms a slope.
In the present invention, the edge portion of the op
Cantor & Colburn LLP
Philogene Haissa
Sanyo Electric Co,. Ltd.
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