The present invention relates generally to a display device having organic light emitting diodes (OLEDs) or polymeric light emitting diodes (PLEDs) as light emitters. More specifically, the present invention relates to a method for encapsulating such display devices.
Organic light emitting diodes (OLEDs) and polymeric light emitting diodes (PLEDs) are becoming increasingly popular for applications such as display, illumination, and backlighting. The heart of a typical organic flat panel display device is a two-dimensional pixel array disposed on a flat, transparent substrate. As shown in
Because of the intrinsic properties of the materials, the pixel array of the above construction is highly susceptible to deterioration caused by oxygen and water vapor. For that reason, it has become common practice to construct a protective cover 30 on the pixel array, preferably encapsulating the pixel array. The protective cover may comprise one or more layers of inorganic or organic materials such as silicon oxides, silicon nitrides and polymers. With the protective cover properly disposed on the light-emitting materials, the display device is, to a certain extent, protected against air and moisture.
Various encapsulation structures are known in the art. For example, Graff et al (U.S. Pat. No. 6,573,652) discloses a display device encapsulated with a barrier stack comprising barrier layers and polymer layers. The barrier layers are disposed adjacent to the display device with a thickness of 100-400 Å, and the polymer layers are disposed adjacent to the barrier layers with a thickness of 1000-10,000 Å. Biebuyck et al. (U.S. Pat. No 5,895,228), Affinito (U.S. Pat. No. 6,268,695), Terasaki et al. (U.S. Pat. No. 6,432,516) and Silvernail et al. (U.S. Pat. No. 6,597,111) also disclose similar layers of protective material disposed on top of the active layers of display devices.
The main purpose of having the protective cover encapsulating the display device, as disclosed in prior art, is to protect the environmentally sensitive display materials against moisture and oxygen in the air. The protective cover in the prior art display devices, however, is not suitable for protecting the light emitting elements in the display device from accidental physical damages, especially during the manufacturing processes.
Thus, it is advantageous and desirable to provide a method to protect a display device having a light-emitting layer from physical damages caused by the scratching by finger nails, dust particles, and metal debris, for example.
A display device, according to the present invention, has a protective structure for protecting the light emitting elements against physical damages. The display device comprises a substrate, an electroluminescent display element disposed on the substrate, one or more layers of barrier against moisture and harmful gaseous elements, and a scratch resistant layer to protect the display element and the barrier from physical damages. The scratch resistant layer can be made of metals, high polymers, glasses and ceramics such that the hardness of the scratch resistant layer is equal to or greater than 2.5 on Moh's scale of hardness. Preferably, the thickness of the scratch resistant layer is equal to or greater than 10 μm.
The above and other objects, features and advantages of the invention will become apparent upon reading the description taken in connection with accompanying drawings, in which:
The electroluminescent display device, according to the present invention, comprises a scratch resistant layer as a part of a protective structure encapsulating the active display materials of the device. A schematic representation of the electroluminescent display device is shown in
First Embodiment of the Invention
The first embodiment of the invention is shown in
Second Embodiment of the Invention
The second embodiment of the invention is shown in
Third Embodiment of the Invention
The third embodiment of the invention is shown in
In the above embodiments, most metals can be used to produce the scratch-resistant layer. The preferred polymers for use to produce the scratch-resistant layer 40, 42 include acrylic plastic, plastic steel, and epoxy resin. As for the first embodiment, the scratch resistant cover 40 can be made of platinum, titanium and ceramic in a sputtering process, for example. Other processes suitable for producing the scratch resistant cover 40 are: chemical vapor deposition of Kelvar, Lexan and lucite, for example; plasma enhanced chemical vapor deposition (PECVD) of ceramic, for example; dipping (similar to electroplating) for producing a layer of metal such as Cu, Ag; and spin-coating of polymers.
In sum, the present invention provides a display device wherein a scratch-resistant layer (40, 42) is disposed in relationship to the electroluminescent display element (26, 24, 22) so as to protect the display element against physical damages such as dust particles, metal debris, and accidental scratching by finger nails. The fabrication process of the device, in general, involves the disposing of a display element on a substrate, and the disposing of the scratch-resistant layer over and/or surrounding the display element. A moisture/oxygen barrier can be provided between the scratch-resistance layer and the display element. Adhesive can be used to provide a hermetic seal for display element and to secure the scratch-resistant layer to the display device. As shown in
It is to be understood that the above-described arrangements are only illustrative of the principles of the present invention. Although the invention has been described and illustrated with respect to exemplary embodiments thereof, the foregoing and various other additions and omissions may be made therein without departing from the scope of the present invention, and the appended claims are intended to cover such modifications and arrangements.