Semiconductor device manufacturing: process – Making device or circuit emissive of nonelectrical signal
Reexamination Certificate
2001-03-28
2004-02-03
Nelms, David (Department: 2818)
Semiconductor device manufacturing: process
Making device or circuit emissive of nonelectrical signal
Reexamination Certificate
active
06686215
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of producing an electroluminescence (hereinafter referred to as “EL”) display device.
2. Description of Related Art
EL display devices using an EL element have recently attracted interest as potential replacements for devices such as CRT or LCD displays.
Also, EL display devices having a thin film transistor (TFT) as a switching element for driving the EL element have been studied and developed.
FIG. 1
shows, in a plan view, one display pixel of an organic EL display device.
FIG. 2
is an equivalent circuit diagram corresponding to one display pixel of an EL display device.
Referring to
FIGS. 1 and 2
, a display pixel is formed in a region enclosed by a gate signal line
51
and a drain signal line
52
. Around the intersection of both signal lines is formed a first TFT
30
as a switching TFT. A source
31
s
of the first TFT
30
also functions as a storage capacitor electrode
55
, and a storage capacitor
70
is formed between the source
31
s
and a storage capacitor electrode
54
which will be described later. The source
13
s
of the TFT
30
is also connected to a gate
41
of a second TFT
40
which drives an organic EL element. A source
43
s
of the second TFT
40
is connected to an anode
61
of the organic EL element while a drain
43
d
is connected to a power source line
53
for driving the organic EL element.
The storage capacitor electrode
54
is disposed in parallel to the gate signal line
51
so as to run through each pixel. The storage capacitor electrode
54
is composed of chromium or the like, and charges are accumulated between the storage capacitor electrode
54
and the capacitor electrode
55
, which also functions as the source
31
s
of the first TFT
30
, via a gate insulating film
12
. The storage capacitor
70
is provided so as to hold a voltage to be applied to the gate
41
of the second TFT
40
.
On a substrate composed of a glass or the like are formed the above-mentioned first and second TFTs
30
,
40
, the lines
51
,
52
,
53
for supplying a gate signal, a data signal, and an element driving power to these TFTs, and the above-referenced storage capacitor electrode
54
. A planarizing insulating film
17
is further formed so as to cover these elements. Over the planarizing insulating film
17
, a transparent electrode using ITO (Indium Tin Oxide), specifically, an anode
61
of an organic EL element
60
, is disposed.
The organic EL element
60
comprises the anode
61
, an emissive element layer comprising an organic compound and formed on the anode
61
, and a cathode formed on the emissive element layer as a common layer for each element. The emissive element layer comprises at least an emissive layer, and may have a laminated structure including, for example, a hole transport layer, an emissive layer, and an electron transport layer, which are disposed in that order from the anode side.
In the organic EL element configured as described above, holes injected from the anode and electrons injected from the cathode are recombined inside the emissive layer to excite organic molecules forming the emissive layer for causing exciton. In the process of radiation and deactivation by the exciton, the emissive layer produces light which is emitted from the transparent anode through the transparent insulating substrate.
Next, a method of forming an emissive element layer of the above-described organic EL element will be described.
For a color display device, in order to emit red (R), green (G), and blue (B) light, it is necessary that the emissive layers for emitting these colors are formed from different materials associated with colors to be emitted. The emissive material layers are formed on the hole transport layer by means of evaporation. More specifically, an emissive material of each of different colors including, for example, red, green, and blue is sequentially evaporated on the corresponding anode
61
in an island pattern corresponding to the anode
61
.
Thus, the emissive layer for emitting each color of R, G, or B is sequentially formed corresponding to the anode
61
for each pixel electrode in a repeated manner, so that, when observed in a plan view, the emissive layers are arranged within the display area of the substrate in a matrix pattern.
When forming the emissive layers, a metal mask
250
having openings at locations corresponding to the display pixels for emitting light of the same color, as shown in
FIG. 3
, is moved in the right or left direction in
FIG. 3
, so that an emissive layer material for each color is evaporated.
FIG. 3
shows a case of evaporating an emissive material of B, with the emissive layers of R and G already formed. Namely, an emissive material of blue, which is placed on an evaporation source
200
, is evaporated and accumulated at locations corresponding to the display electrodes for the B color.
However, the metal mask
250
for use in evaporation as shown in
FIG. 3
, which has openings
251
at locations corresponding to the emissive layers of the same color, causes problems such as the following. When the thickness of the metal mask is h, and the width of the opening (the horizontal direction in
FIG. 3
) is d, and the width d is too large with regard to the thickness h, the emissive material evaporated from the evaporation source is deposited not only on the intended display pixel, but spreads to areas of the emissive layer of an adjoining pixel electrode designed to emit a different color. For example, on a pixel electrode in which the emissive material of G is already evaporated and accumulated, emissive material for B color for the adjacent pixel can be mixed such that a mixed color of B and G is generated. This leads to a disadvantage that intended color display can not be obtained.
SUMMARY OF THE INVENTION
The present invention was conceived in view of the aforementioned problems of the related art and aims to provide a method of producing an EL display device in which spread of an emissive layer material onto an adjoining pixel electrode is prevented, thereby reducing color mixture and enabling more accurate and consistent display of desired colors.
In accordance with the present invention, there is provided a method of producing an electroluminescence display device comprising an emissive layer for emitting a color formed between an anode and a cathode constituting a pixel electrode, in which provided on said anode to form said emissive layer is a mask having a thickness h and an opening width d determined between adjacent display pixels such that the thickness h and the opening width d satisfying the relationship h>n×d, wherein n>1.
Further, in the above method, it may be preferable that the thickness h and the opening width d of the mask satisfy a relation of h>n×d where 1<n≦2.5.
Further, in the above method, said mask may be formed from a metal or semiconductor.
As described above, in accordance with the present invention, the emissive layer is formed using a mask having an appropriate thickness with respect to the width of the opening, so that mixture of colors between emissive layers in adjoining pixel electrodes can be reduced. It is therefore possible to provide an EL display device capable of displaying pure colors.
REFERENCES:
patent: 5937272 (1999-08-01), Tang
patent: 6087772 (2000-07-01), Ootsuki et al.
patent: 6255775 (2001-07-01), Ikuko et al.
Office Action from Taiwan Patent Application Ser. No. 090107326.
Cantor & Colburn LLP
Hoang Quoc
Nelms David
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