Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure – Encapsulated
Reexamination Certificate
2001-05-25
2004-01-13
Tran, Minh Loan (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
Encapsulated
C313S489000, C313S492000, C313S493000, C313S505000, C313S512000
Reexamination Certificate
active
06677620
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an organic EL (ElectroLuminescence) element and, more particularly, to an organic EL element in which an organic EL layer is hermetically sealed with a hermetic sealing cap, and a method of manufacturing the same.
EL is a phenomenon in that a certain type of phosphor emits light upon application of an electric field, and an element that utilizes this phenomenon is an EL element. In the structure of an organic EL element, an organic layer made of a light-emitting material using an organic compound is sandwiched between two electrodes. The arrangement of the organic layer includes a multilayered structure of a light-emitting layer made of a fluorescent organic solid such as anthracene and a hole injection layer made of a triphenylamine derivative or the like. Another organic layer is also available which is comprised of a multilayered structure of a light-emitting layer and an electron injection layer made of a perylene derivative, or a multilayered structure of a hole injection layer (hole transport layer), an EL light-emitting layer, and an electron injection layer (electron transport layer). In the organic EL element, a multilayered structure interposed between two electrodes is generally formed on a substrate.
Such an organic EL element utilizes light emitted when electrons injected to the light-emitting layer are recombined with holes. With this organic EL element, high-luminance light emission of several 100 cd/m
2
to several ten 1,000 cd/m
2
can be obtained with a voltage of about 10 V, and the response speed is also high.
The organic EL element has a disadvantage in that it is not resistant to water. For example, even a very small amount of water can separate the light-emitting layer and electrode layer from each other, or denature the materials constituting the light-emitting layer and the like. In this case, a non-emission portion called a dark sport is formed to degrade the quality of emission. Therefore, when a conventional organic EL element is driven in the atmosphere, its light-emitting characteristics quickly degrade. In order to obtain a practical organic EL element, the element must be sealed so water or the like will not enter the light-emitting layer.
As a structure for sealing the organic EL element, a structure in which a resin or the like is directly applied to the organic EL element, or a hollow structure filled with a gas or liquid is available.
FIG. 3
shows the arrangement of an organic EL element to which a conventional sealing structure (filled-type structure) is applied. In the organic EL element shown in
FIG. 3
, anodes
13
, an organic EL layer
14
, and cathodes
15
are sequentially formed on a glass substrate
12
. For example, the organic EL layer
14
has a multilayered structure of a hole transport layer and an EL light-emitting layer. In a filled-type structure, the organic EL element formed on the glass substrate
12
is covered with a hermetic sealing cap
16
fixed by an adhesive
41
, and the interior of the hermetic sealing cap
16
is filled with an inert gas.
As the material of the sealing cap
16
, for example, a glass, metal, or plastic is used. As the adhesive
41
for bonding the glass substrate
12
and sealing cap
16
with each other, a resin that sets at room temperature or a resin that sets upon irradiation with ultraviolet rays is used because the organic EL element has a low heat resistance. When the sealing cap
16
is to be fixed on the glass substrate
12
by using such an adhesive, after the adhesive
41
is applied to the bonding surface of the glass substrate
12
or sealing cap
16
, operation of fixing the glass substrate
12
and sealing cap
16
is necessary.
When the organic EL element as described above is to be downsized, the area of a region that does not contribute to light emission must be reduced. A region that does not contribute to light emission includes a portion necessary for sealing adhesion, a region between a sealing adhesion portion and the end of a light-emitting region, an electrode (anode) extraction portion, and the like. An electrode with a thickness of about 100 nm, which is necessary for causing the internal organic EL element to emit light, is formed on the surface of the glass substrate
12
. The glass substrate
12
itself has a warp or undulation of at least about several &mgr;m.
Hence, the warp or undulation described above and a three-dimensional shape (step) formed by the electrode are present on that portion of the glass substrate
12
which is to be bonded to the sealing cap
16
. When the glass substrate
12
and sealing cap
16
are brought into direct contact with each other, they do not come into tight contact with each other but leave many gaps between them. For this reason, the adhesive
41
is applied to a certain constant thickness (10 &mgr;m to several 100 &mgr;m) to absorb the three-dimensional shape, and the glass substrate
12
and sealing cap
16
are bonded to each other to form no gaps between them. Since the adhesive
41
is applied thick in this manner, when the glass substrate
12
and sealing cap
16
are aligned with and pressed against each other, the sandwiched adhesive
41
may be squeezed and extend to likely attach to the organic EL element.
When the adhesive
41
attaches to the organic EL element, a stress is generated to act on the organic EL element regardless of whether the adhesive
41
is set/unset. The organic EL element which is very thin is thus damaged to form a non-emission portion. For this reason, squeezing of the adhesive
41
must be controlled. When the amount of adhesive
41
is reduced, although squeezing does not occur, the three-dimensional shape cannot be sufficiently absorbed by the adhesive
41
, and adhesion becomes poor to form gaps, so hermeticity cannot be held.
The adhesive
41
used for sealing the organic EL element must be set at a temperature which is low to such a degree that it does not degrade the organic EL element. Also, a gas that adversely affects the organic EL element during setting should not be generated. In addition, the adhesive
41
must have a low permeability so that hermeticity can be held over a long period of time.
From the above requirements, the adhesive used for sealing the organic EL element must have the following characteristics:
1. A warp or undulation on the bonding surface between the sealing cap and glass substrate, and a step formed by an extraction interconnection can be planarized sufficiently.
2. The setting temperature (adhesive fixing temperature) is lower than a temperature that the organic EL element can stand.
3. No gas toxic to the organic EL element is generated during setting.
4. The set adhesive has a low permeability.
5. The interface of the adhesive has low adhesion properties and water permeation from the interface with the hermetic sealing cap or glass substrate is sufficiently small.
Although an ultraviolet-curing epoxy resin which does not require heating can satisfy the required characteristics of items 1 to 3, and 5, its permeability is not very low, which is disadvantageous in holding the hermeticity. In contrast to this, although a thermosetting epoxy resin has a lower permeability than that of the ultraviolet-curing epoxy resin, the gas generated during setting degrades the organic EL element, and the temperature necessary for setting exceeds the heat resistance of the organic EL element. Therefore, this epoxy resin does not satisfy the items 2 and 3, and cannot be adopted for sealing the organic EL element.
Therefore, conventionally, the ultraviolet-curing resin is used, although its hermeticity holding level is insufficient from the viewpoint of the service life of the organic EL element. Also, the thickness of the adhesive is decreased as much as possible in order to compensate for the low permeability. When the material of the sealing cap is a conductive metal, partly because of the molding precision of the sealing cap, the thickness of the adhesive cannot be made thin when preventing the organic EL elem
Ishii Ikuko
Kondo Yuji
Tran Minh Loan
Tran Tan
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