Electric lamp and discharge devices – With luminescent solid or liquid material – Solid-state type
Reexamination Certificate
2002-09-13
2004-08-10
Tran, Minhloan (Department: 2826)
Electric lamp and discharge devices
With luminescent solid or liquid material
Solid-state type
C257S040000, C257S043000, C257S099000, C257S103000, C313S504000, C313S506000
Reexamination Certificate
active
06774561
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a light-emitting device and a process for production thereof and, more particularly, to a light-emitting device having an emission layer held between electrodes and a process for production thereof.
BACKGROUND ART
An organic electroluminescence (referred to as EL hereinafter) device, which is a spontaneous light-emitting device (referred to as light-emitting device hereinafter), has an organic film including an organic emission layer between an anode and a cathode.
FIG. 4
is a sectional view showing the structure of one example of such light-emitting devices. The light-emitting device shown in this figure has a lower electrode
102
as an anode of metallic material formed on a substrate
101
and an organic layer
106
including an organic hole injection layer
103
, an organic hole transporting layer
104
, and an organic emission layer
105
or the like, which are sequentially laid one over the other on the lower electrode
102
. And, on this organic layer
106
is formed an upper electrode
107
as a cathode which is a thin film of metallic material transparent to light and is further formed a transparent conductive film
108
to reduce the resistance of the upper electrode
107
as a cathode.
The light-emitting device of such structure is a display element of so-called “top emitting type”, which works in such a way that the light generated by the organic emission layer
105
is reflected by the lower electrode
102
of metallic material and is allowed to emanate through the upper electrode
107
placed opposite to the substrate
101
.
Moreover, production of the light-emitting device of such structure starts with forming a layer of metallic material on the substrate
101
by any process adequately selected from various processes such as sputtering, resistance heating vapor deposition, and electron beam vapor deposition, and forming the lower electrode
102
by patterning the layer of metallic material. Subsequent steps are sequential deposition of materials for the organic layers
103
to
105
, the upper electrode
107
, and the transparent conductive film
108
through a deposited mask, and the deposition is followed by patterning to form the organic layer
106
, the upper electrode
107
, and the transparent conductive layer
108
.
However, the display device and the process for production thereof as mentioned above have the following problem. Namely, all the layers of metallic material tend to have polycrystalline structure no matter whether they are formed by sputtering, resistance heat vapor deposition, or electron beam vapor deposition. As the result, the lower electrode
102
formed by patterning the layer of metallic material has projections on its surface due to marked surface roughening, as shown in
FIG. 5
(an enlarged sectional view), although not so serious as the transparent anode formed from ITO (indium tin oxide).
Consequently, the organic layer
106
formed on the lower electrode
102
becomes locally thin at spots corresponding to projections, with the result that the distance d across the organic layer
106
between the lower electrode
102
and the upper electrode
107
becomes locally short and the electric field concentrates at such spots to cause leakage current.
This leakage current does not help the light-emitting device to emit light but decreases the efficiency of the light-emitting device. Moreover, extremely concentrated leakage current results in a short circuit between the lower electrode
102
and the upper electrode
107
, thereby disabling the light-emitting device from light emission. This is the cause for non-emitting spots so-called dark spots in the organic EL display.
A possible way to prevent leakage current is to form the lower electrode
102
′ from an electrically conductive material, such as chromium oxide, which gives a flat film surface, as shown in FIG.
6
. However, the electrically conductive material in oxide form has a low reflectivity and readily transmits light, so that the lower electrode
102
′ made of the electrically conductive material permits the light h reaching it from the emission layer
105
as one of the organic layers
106
to be absorbed toward the substrate
101
. This results in a decrease in the amount of light h emanating from the upper electrode
107
, which in turn leads to a decease in emission efficiency.
It is an object of the present invention to provide a light-emitting device of top emission type and a process for production thereof, the light-emitting device keeping a stable emitting efficiency without leakage current.
DISCLOSURE OF INVENTION
The present invention to achieve the above-mentioned object covers a light-emitting device composed of a lower electrode which is laid on a substrate, an organic layer including at least an emission layer which is laid on the lower electrode, and an upper electrode transparent to light which is laid on the organic layer, characterized in that the lower electrode is of laminate structure consisting of a metallic material layer and a layer of buffering thin film which is formed on the metallic material layer. The buffering thin film is made of any oxide of the metallic material constituting the metallic material layer, the oxide having a higher conductivity than the organic layer, or made of an oxide of chromium.
Also, according to the present invention, the light-emitting device is produced by a process including steps of forming a lower electrode on a substrate, forming on the lower electrode an organic layer including an emission layer, and forming above the substrate an upper electrode transparent to light such that the emission layer is held between the lower electrode and the upper electrode, characterized in that the step of forming the lower electrode includes additional steps of forming a buffering thin film on a metal film formed on the substrate and patterning the metal film and buffering thin film, thereby forming the lower electrode of laminate structure consisting of the metallic material layer and the buffering thin film. The buffering thin film is made of any oxide of the metallic material constituting the metal layer, the oxide having a higher conductivity than the organic layer, or made of an oxide of chromium.
The above-mentioned light-emitting device and production process are characterized in that the surface layer of the lower electrode is a buffering thin film which is made of any oxide of the metal constituting the underlying metallic material layer, the oxide having a higher conductivity than the organic layer, or made of an oxide of chromium. In general, a metal film has a rough surface due to polycrystalline structure, whereas a film of an oxide of the metallic material constituting the metal film has a less rough surface. In addition, a buffering thin film made of an oxide of chromium has a less rough surface than the metal film independently of the metal film underneath. Moreover, the buffering thin film functions as the lower electrode if it is made of any oxide of the metal constituting the metallic material layer, the oxide having a higher conductivity than the organic layer, or made of a chromium oxide which has the highest conductivity among oxides. Thus, the foregoing structure ensures a uniform space between the lower electrode whose metallic material layer has a mildly rough surface owing to the buffering thin film layer constituting the surface layer and the upper electrode transparent to light which is laid on the lower electrode with an organic layer interposed between them.
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Australian Examinantion Report.
Kananen Ronald P.
Rader & Fishman & Grauer, PLLC
Sony Corporation
Tran Minhloan
Tran Tan
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