Electric lamp and discharge devices – With luminescent solid or liquid material – Solid-state type
Reexamination Certificate
2000-12-11
2003-07-15
Wong, Don (Department: 2821)
Electric lamp and discharge devices
With luminescent solid or liquid material
Solid-state type
C313S310000, C315S169300
Reexamination Certificate
active
06593691
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an EL (electro-luminescence) display device fabricated by forming a semiconductor device (a device utilizing a semiconductor thin film; typically a thin film transistor) onto a substrate. The present invention further relates to an electrical equipment including such an EL display device as a display section.
2. Description of the Related Art
Recently, a technique for forming a thin film transistor (hereinafter referred to as TFT) onto a substrate has significantly advanced, and its application to an active-matrix display device has been developed. In particular, the TFT employing a polysilicon film therein has a field effect mobility higher than that of the conventional TFT employing an amorphous silicon film, and therefore, can operate at higher speed. Thus, a control function for pixels, that is conventionally performed by an external driver circuit provided at the outside of the substrate, can be performed by a driver circuit that is provided on the same substrate as the pixels.
The active-matrix display device as mentioned above can provide various advantages such as reduction in the manufacturing cost, downsizing of the display device, improvement of the yield, reduction in the throughput or the like, when various circuits and/or devices are fabricated on one and the same substrate. Thus, this kind of active-matrix display device has drawn much attention.
In an active-matrix EL display device, a switching device employing a TFT (hereinafter referred to as switching TFT) is provided at each pixel, and each of the respective switching TFTs allows a corresponding drive device for controlling current (hereinafter referred to as current-controlling TFT) to drive, thereby causing an EL layer (more strictly speaking, a light emitting layer) to emit light. An exemplary EL display device is described, for example, in Japanese Patent Application Laid-Open No. Hei. 10-189252.
The EL display device includes a device section composed of a cathode, an EL layer, and an anode (hereinafter, the device composed of these portions is referred to as EL device). When a film resistance of the anode in the device section increases, the in-plane distribution of electrical potentials in the anode becomes non-uniform due to the voltage drop, thereby resulting in disadvantages such as deviations in the light intensity of the EL device.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide an EL display device having the structure capable of lowering a film resistance of an anode in an EL device or exhibiting any corresponding advantages. Furthermore, another objective of the present invention is to provide electrical equipment having a display section which operates stably by employing such an EL display device as the display section.
The present invention will be described below with reference to FIG.
1
. In
FIG. 1
, reference numeral
101
denotes a substrate having an insulating surface. As the substrate
101
, for example, an insulating substrate such as a quartz substrate can be used. Alternatively, various kinds of substrate, such as a glass substrate, a ceramic substrate, a crystallized glass substrate, a metal substrate, or a plastic substrate, can be used by providing an insulating film on a surface thereof.
On the substrate
101
, pixels
102
are formed. Although only three of the pixels are illustrated in
FIG. 1
, a higher number of pixels are actually arranged in matrix. Further, only one of the three pixels will be described below, but the other pixels have the same configuration as the explained one.
In each of the pixels
102
, two TFTs are formed; one of them is a switching TFT
103
, and the other is a current-controlling TFT
104
. A drain of the switching TFT
103
is electrically connected to a gate of the current-controlling TFT
104
. Furthermore, a drain of the current-controlling TFT
104
is electrically connected to a pixel electrode
105
(which, in this case, also functions as a cathode of an EL device). The pixel
102
is thus formed.
Various wirings of the TFT as well as the pixel electrode can be formed of a metal having a low resistivity. For example, an aluminum alloy may be used herein for this purpose.
Following the fabrication of the pixel electrode
105
, an insulating compound (referred to as alkaline compound hereinafter)
106
containing an alkaline metal or an alkaline-earth metal is formed. It should be noted that the outline of the alkaline compound
106
is indicated by a dotted line in
FIG. 1
because the compound
106
has a thickness which is as thin as several nanometers, and it is not clear whether the compound
106
is formed as a layer or in an island-shape.
As the above-mentioned alkaline compound
106
, lithium fluoride (LiF), lithium oxide (Li
2
O), barium fluoride (BaF
2
), barium oxide (BaO), calcium fluoride (CaF
2
), calcium oxide (CaO), strontium oxide (SrO), or cesium oxide (Cs
2
O) can be used. Since these are insulating materials, electrical short-circuiting between the pixel electrodes does not occur even when the compound
106
is formed as a layer.
It is of course possible to use a known conductive material such as a MgAg electrode as the cathode. However, in such a case, in order to avoid electrical short-circuiting between the pixel electrodes, the cathode itself has to be selectively formed or patterned into a certain shape.
Once the alkaline compound
106
is formed, an EL layer
107
(an electro-luminescence layer) is formed over the compound
106
. Any known material and/or structure can be employed for the EL layer
107
. More specifically, with respect to the structure of the EL layer, only a light emitting layer for providing sites for the carrier recombination may be included in the EL layer. Alternatively, if necessary, an electron injection layer, an electron transport layer, a hole transport layer, an electron blocking layer, a hole device layer, or a hole injection layer may be further layered to form the EL layer. In the present application, all of those layers intended to realize injection, transport or recombination of carriers are collectively referred to as the EL layer.
As an organic material to be used as the EL layer
107
, either a low-molecular type organic material or a polymer type (high-molecular type) organic material can be used. However, it is desirable to use a polymer type organic material which can be formed by a film-formation method that can be easily performed, such as a spin coating method, a printing method, or the like.
The structure illustrated in
FIG. 1
is an example of the monochrome color light-emitting type in which an EL layer for emitting a monochrome color light, such as a red color, a blue color, a green color, a white color, a yellow color, an orange color, a purple color or the like, is used for displaying a monotone image. The EL layer for emitting any monochrome color light as mentioned above may be formed of known materials.
Over the EL layer
107
, a transparent conductive film is formed as an anode
108
. As the transparent conductive film, a compound of indium oxide and tin oxide (referred to as ITO), a compound of indium oxide and zinc oxide, tin oxide, or zinc oxide (ZnO) can be used.
In the present application, a film resistance of the whole anode obtained by calculating an average of a film resistance for a region where a metal film
109
and the anode
108
are layered and a film resistance for only the anode (in other words, a film resistance of the whole portion electrically connected to the anode) will be referred to as the average film resistance of the anode. By providing the metal film
109
over the anode, the average film resistance in the anode can be decreased. Furthermore, the metal film
109
also functions as a light shielding film.
As a deposition technique for the metal film
109
, a vapor deposition method is desirable in view of any possible damage to the anode during the deposition process.
In addition, upon the provision of the me
Ishimaru Noriko
Nishi Takeshi
Cook Alex McFarron Manzo Cummings & Mehler, Ltd.
Tran Thuy Vinh
Wong Don
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