Semiconductor device manufacturing: process – Having organic semiconductive component
Reexamination Certificate
2002-06-25
2004-02-17
Elms, Richard (Department: 2824)
Semiconductor device manufacturing: process
Having organic semiconductive component
C438S064000, C438S116000
Reexamination Certificate
active
06692986
ABSTRACT:
FIELD OF THE INVENTION
The invention generally relates to a method of encapsulating components based on organic semiconductors. Preferably, it relates especially to organic light-emitting diodes, in which a housing is bonded adhesively to a substrate.
BACKGROUND OF THE INVENTION
Components whose functioning is based on the use of organic semiconductors must be given effective protection against ambient influences, and especially against degradation caused by air or moisture. This purpose is generally served by a housing, which may also, for example, be a flat cover.
Components based on organic semiconductors are, in particular, organic light-emitting diodes (OLEDs). Light-emitting diodes of this kind feature organic monomers or polymers arranged between electrodes, with one electrode being transparent. When a voltage is applied to the electrodes, light is emitted. For this purpose OLEDs typically feature an organic electroluminescent material (emitter), an organic hole transport material, and an organic electron transport material. These materials, and the cathode material too, require protection against degradation caused by air (oxygen) and water, for which efficient capsuling is needed.
The capsuling of OLEDs can take place in a variety of ways: for example, by means of glass solders, i.e., by joining (glass) parts using a glass solder (German patent application file ref. 198 45 075.3). Already known as well is an electroluminescent system wherein the electroluminescent element is enclosed in a housing composed of a substrate, which carries the electroluminescent element, and a cover layer, made of a low-melting metal or a corresponding alloy and provided with an electrically conducting adhesive film (WO 97/46052). A disadvantage here is that the relatively high temperatures needed for processing the glass solder and/or the metal or alloy from the melt may result in damage to the electroluminescent element.
An organic electroluminescent device with a flat cover is known from EP 0 468 440 B 1. Atop the cathode in this device is a protective layer composed of a mixture of at least one component of the organic electroluminescent medium and at least one metal having a work function in the range from 4 to 4.5 Ev. The protective layer is produced by coevaporation of the aforementioned materials, although this involves a great deal of complexity.
“Applied Physics Letters”, Vol. 65 (1994), pages 2922 to 2924 discloses covering the OLED on a glass substrate with a glass plate and adhesively bonding said plate to the glass substrate; bonding can be carried out using a commercial epoxy adhesive. The use of an epoxide for sealing organic light-emitting devices is also known from the U.S. Pat. Nos. 5,703,394 and 5,747,363.
DE 196 03 746 A1 discloses an electroluminescent device (with light-emitting organic material) whose capsuling comprises a multilayer system. This multilayer system is composed of at least one layer of plastic, and a metallic layer. In addition, there may be what is called a getter layer, which is embedded between two plastic layers. The plastic layers may consist, inter alia, of an epoxy resin.
In investigations on organic light-emitting diodes—for example, in storage tests at a temperature of 85° C. and a relative humidity of 85%—it nevertheless proved impossible to find any commercially available adhesive which neither corroded the base metals used as cathode material nor impaired the light-emitting materials.
SUMMARY OF THE INVENTION
It is an object of an embodiment of the invention, therefore, to specify a method of encapsulating components based on organic semiconductors which on the one hand permits hermetic capsuling, so that harmful environmental effects are ruled out, and on the other hand does not lead to damage to the materials used in the components.
An object can be achieved in accordance with an embodiment of the invention by carrying out adhesive bonding using a UV-curable reactive adhesive comprising the following components:
an epoxy resin,
a hydroxy-functional reaction product of an epoxide compound with a phenolic compound,
a silane-type adhesion promoter, and
a photoinitiator, and also
if desired, filler.
The stated technical problem can be solved in accordance with an embodiment of the invention by joining the given parts by using a specially formulated adhesive based on epoxy resin. The given parts comprise a housing and a substrate which is the location for the organic semiconductor and the other materials needed for the functioning of the component: for example, metals as conductor tracks. Glass substrates in particular can be used, although plastic film substrates or plastic/glass composites may also be used. The housing may be a plate, particularly a glass plate, and is preferably a cover, made in particular from glass, although it may also be of ceramic or metal.
The adhesive used in accordance with an embodiment of the invention for constructive adhesive sealing, which can be applied without great effort, can be advantageously liquid or low-melting and therefore wetting. It is therefore particularly suitable for capillary gluing, i.e., for filling thin joints, but may alternatively be used as a casting resin or coating material.
The use of the adhesive of an embodiment of the invention produces the following advantages, including:
cost effective, automatable process;
rapid process;
low temperature process, thus no damage to the organic semiconductor;
no cumbersome insulation of adjacent conductor tracks which pass through the adhesion zone, owing to the electrically insulating nature of the adhesive.
Special advantages of the adhesives include:
one-component system, storable at room temperature for at least 1 year;
no outgassing of volatile constituents damaging to the functioning of the component;
high adhesion to glass over a wide temperature range;
flexibility sufficient over a wide temperature range, thereby minimizing mechanical stress as a result of thermal loading;
optical transparency;
higher O
2
and H
2
O diffusion barrier;
electrically insulating activity;
ability to be processed under inert conditions;
rapid curing by UV irradiation.
The specific formulation of the adhesive gives it, in particular, high compatibility with components and also an effective air and moisture barrier effect. Accordingly, this adhesive is outstandingly suitable for capsuling (encapsulating) components based on organic semiconductors, especially light-emitting diodes.
When using covers which are bonded only at the edges, rather than plates, it is possible to avoid flat bonding and, consequent thereon, additional mechanical stress on the component.
The adhesive can be applied in particular, by capillary gluing, thus producing an extremely small adhesive joint of from 1 to 30 &mgr;m, generally <10 &mgr;m. The result is a minimal area of attack for oxygen and water. As a result of the specific cationically initiated curing of the adhesive, i.e., the UV cure, “one” polymer molecule is obtained, so to speak, which is free of low molecular mass, outgassable constituents harmful to the performance of the diodes. Moreover, it is possible to apply the adhesive in an inert gas atmosphere, which is necessary for the handling of the air-sensitive metal electrode materials, such as calcium. As a consequence of the UV-curability, a rapid process with a one-component resin is made possible. Encapsulation may also take place in addition to flat inorganic protective layers that are present on the components; such protective layers include, for example, SiO
2
or Si
3
N
4
.
UV curing of the reactive adhesive may be followed advantageously by a thermal treatment, preferably up to a temperature of 120° C. The lower temperature limit is generally about 10 to 20° C. below the glass transition temperature of the cured adhesive. As a result of the thermal treatment (aftercure), the barrier effect of the adhesive film toward water and oxygen can be increased further.
The epoxy resin in the reactive adhesive may be an aliphatic, cycloaliphatic or aromatic epoxide, with pre
Bayer Heiner
Rogler Wolfgang
Roth Wolfgang
Elms Richard
Harness & Dickey & Pierce P.L.C.
Osram Opto Semiconductors GmbH
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