Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2000-09-12
2003-12-09
Kelly, Cynthia H. (Department: 1774)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S917000, C313S506000, C313S512000, C257S099000, C257S100000
Reexamination Certificate
active
06660409
ABSTRACT:
BACKGROUND OF THE INVENTION
1) Field of the Invention
The present invention relates to a protective film for use in sealing or protection of various electronic devices such as organic electroluminescence devices, etc. used in light emitting devices, etc. in various display devices or light sources or backlight in display devices or optical communication systems, and a process for producing the same.
2) Related Art of the Invention
Generally, electronic devices are protected by sealing to some extent, because they are highly susceptible to external circumstance factors such as moisture, heat, etc., and recent trends toward higher density and higher precision of electronic devices are requiring highly reliable sealing, and thus intensive studies have been so far fostered.
Materials so far used for this purpose are shifting from the inorganic system to the organic/inorganic complex systems taking the versatility of organic materials into consideration. It is now an important problem how to suppress degradation of organic materials very easily susceptible to external circumstance factors such as moisture, heat, stress, etc.
It is organic electroluminescence devices that have recently attracted attention among devices using such organic materials.
Electroluminescence device is a light-emitting device based on electroluminescence of solid fluorescent substances, and inorganic electroluminescence devices based on inorganic light-emitting materials have been so far practically applied to the backlight of liquid crystal display, flat display, etc.
Electroluminescence devices based on organic materials, on the other hand, have been long studied in various ways, but very poor light-emitting efficiency has been a bottleneck to full scale practical application study.
However, C. W. Tang et al of Eastman Kodak Co. proposed in 1987 an organic electroluminescence device in a functionally separated type, stacked layer structure, where organic materials were divided into two layers, i.e. a hole transport layer and a light-emitting layer, and disclosed that a high luminance e.g. 1,000 cd/m
2
or more could be obtained even at a low voltage such as 10 V or less [C. W. Tang and S. A. Vanslyke: Appl. Phys. Lett., 51 (1987), 913, etc.]. After the disclosure the organic electroluminescence devices were suddenly highlighted and extensive studies have been made of organic electroluminescence devices in a similar functionally separated type, stacked layer structure, some of which are now practically used.
Explanation will be made below of the conventional organic electroluminescence device, referring to FIG.
7
.
FIG. 7
is a cross-sectional view showing the essential part of the conventional organic electroluminescence device, where reference numerals have the following meanings:
1
: substrate,
2
: anode,
3
: organic thin film layer,
4
: hole transport layer,
5
: light-emitting layer and
6
: cathode.
As shown in
FIG. 7
, the conventional organic electroluminescence device comprises transparent or opaque substrate
1
of glass, etc., anode
2
made from a transparent conductive film of ITO, etc. formed on substrate
1
by sputtering, resistance-heated vapor deposition, etc., hole transport layer
4
made from N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-diphenyl-4,4,-diamine (hereinafter referred to as TPD), etc., formed on anode
2
by resistance-heated vapor deposition, etc., light-emitting layer
5
made from 8-hydroquinoline aluminum (hereinafter referred to as Alq
3
), etc. formed on hole transport layer
4
by resistance-heated vapor deposition, etc., and cathode
6
made from a metal film, etc. formed on light-emitting layer
5
by resistance-heated vapor deposition, etc., where hole transport layer
4
and light-emitting layer
5
constitute organic thin film layer
3
in FIG.
7
.
When a DC voltage is applied or direct current is passed between anode
2
as a plus electrode and cathode
6
as a minus electrode in the organic electroluminescence device in the stacked layer structure, holes are injected into light-emitting layer
5
from anode
2
through hole transport layer
4
and electrons are injected into light-emitting layer
5
from cathode
6
. In light-emitting layer
5
, holes and electrons are recombined to form excitons and when the excitons thus formed are shifted from the excited state to the ground state light emission phenomena take place. Light emission wavelength can be changed by changing the stacked layer structure of organic thin film layer
3
or materials of light-emitting layer
5
.
To improve light emission characteristics of such an organic electroluminescence device, studies have been made of 1) improvement of the structure of organic thin film layer, i.e. light-emitting layer, hole transport layer, etc. or organic materials for these layers and
2
) improvement of anode and cathode materials.
For example, to lower the barrier between the cathode and the light-emitting layer, thereby facilitating injection of electrons into the light-emitting layer in case of
2
), materials of small work function and high electroconductivity, e.g. Mg—Ag alloys (U.S. Pat. No. 4,885,211), Al—Li alloys (JP-A-5-121172), etc. were proposed, and these materials have been widely used even now.
However, these alloy materials undergo corrosion or oxidation through reactions with moisture or oxygen in air because of their high activities and chemical unstableness. Such cathode corrosion or oxidation gives rise to considerable growth of non-emitting regions, so called dark spots (D.S.) in the light-emitting layer, and is a cause for characteristic degradation with time of organic electroluminescence devices.
Generally, structural changes due to reactions with moisture or oxygen takes place not only in cathode, but also in organic materials used for the organic thin film layer including the light-emitting layer, the hole transport layer, etc., and thus is likewise a cause for D.S. growth.
As a result of studies on D.S. growth from various viewpoints, the present inventors have found that even such a very small amount of moisture as found in vacuum of about 10
−4
Torr can promote D.S. growth. To prevent reactions of cathode materials or organic thin film layer materials with moisture or oxygen, thereby completely eliminating D.S. growth and improving durability and reliability of organic electro-luminescence devices, it is necessary to seal the entire organic electroluminescence devices.
For sealing the organic electroluminescence devices, studies have been made so far mainly of the following two procedures. One procedure is to form a protective film on the outer surface of an organic electroluminescence device by vacuum film formation such as vapor deposition, etc., and another procedure is to seal an organic electroluminescence device with a shielding material such as a glass cap, etc.
As to the former procedure for forming a protective film, thereby sealing an organic electroluminescence device, for example, JP-A-6-96858 discloses forming GeO, SiO, AlF
3
, etc. on the outer surface of the device by ion plating.
Furthermore, JP-A-10-261487 discloses formation of Si
3
N
4
, diamond-like carbon film, etc. on the outer surface of the device by ECR plasma CVD.
Still furthermore, JP-A-7-211455 discloses formation of a protective film comprising a water-absorbable material having a water absorption percentage of not less than 1% and a moisture-resistant material having a moisture absorption percentage of not more than 0.1%.
As to the latter procedure for sealing an organic electroluminescence device with a shielding material, the following procedures are available: procedure of providing a glass plate on the outer surface of a back electrode and sealing silicone oil into between the back electrode and the glass plate, as already used in case of inorganic electroluminescence devices; procedure of forming a protective film comprising an insulating inorganic compound, followed by shielding with an electrically insulating glass or electrically insulating hermetic
Furukawa Katsuhiko
Gao Dawei
Gyoutoku Akira
Hamano Takafumi
Hara Shintaro
Garrett Dawn L.
Kelly Cynthia H.
Panasonic Communications Co., Ltd
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