Electric heating – Metal heating – By arc
Reexamination Certificate
2001-02-08
2003-08-19
Evans, Geoffrey S. (Department: 1725)
Electric heating
Metal heating
By arc
C228S245000, C228S246000
Reexamination Certificate
active
06608283
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to the sealing of organic light emitting diode (OLED) devices. In particular, the present invention is directed to an apparatus and method of solder-sealing an active matrix OLED display.
BACKGROUND OF THE INVENTION
An OLED is a thin film structure formed on a substrate. A light emitting layer of a luminescent organic solid, as well as adjacent semiconductor layers, are sandwiched between a cathode and an anode. The semiconductor layers may be either hole-injecting or electron-injecting layers. The light emitting layer may consist of multiple sublayers. When a potential difference is applied across the device, negatively charged electrons move from the cathode to the electron-injecting layer and finally into the layer(s) of organic material. At the same time, positive charges, typically referred to as holes, move from the anode to the hole-injection layer and finally into the same light emitting organic layer. When the positive and negative charges meet in the organic material layer(s), they recombine and produce photons.
In a typical matrix-addressed OLED display, numerous OLEDs are formed on a single substrate and arranged in groups in a grid pattern. Several OLED groups forming a column of the grid may share a common cathode, or cathode line. Several OLED groups forming a row of the grid may share a common anode, or anode line. The individual OLEDs in a given group emit light when their cathode line and anode line are activated at the same time.
OLEDs have a number of beneficial characteristics. These characteristics include a low activation voltage, fast response when formed with a thin light emitting layer, and high brightness in proportion to the injected electric current. Depending on the composition of the organic material making up the light emitting layer, many different colors of light may be produced, ranging from visible blue, to green, yellow and red.
OLEDs, however, are susceptible to damage resulting from exposure to the atmosphere. The fluorescent organic material in the light emitting layer can be reactive. Exposure to moisture and oxygen may cause a reduction in the useful life of the light emitting device. OLEDs are extremely sensitive to moisture. Their performance rapidly degrades in the presence of a minute amount of moisture. The organic materials are susceptible to reacting with constituents of the atmosphere such as water and oxygen. Additionally, the materials that typically comprise the cathode and anode may react with oxygen and may be negatively affected by oxidation.
One disadvantage of oxygen and moisture penetration into the interior of the OLED is the potential to form metal oxide impurities at the metal-organic material interface. In a matrix addressed OLED, these metal oxide impurities may cause separation of the cathode or anode from the organic material. Oxidation sensitive cathode materials such as Mg—Ag or Al—Li are especially susceptible. The result may be dark, non-emitting spots at the areas of separation due to a lack of current flow.
Edge shorting between the cathode and anode layers is a further problem affecting most conventional OLED devices. Edge shorting reduces the illumination potential of the display devices. For the reasons set forth above, exposing a conventional OLED to the atmosphere shortens its life. To obtain a practical, useable OLED device, it is necessary to protect or seal the device, so that water, oxygen, etc., do not infiltrate the light emitting layer or oxidize the electrodes.
Methods commonly employed for protecting or sealing inorganic electroluminescent devices are typically not effective for sealing OLEDs. Resin coatings have been used to protect inorganic electroluminescent devices, but are not suited for OLEDs. The solvent used in the resin coating solution tends to infiltrate the light emitting layer, degrading the light emission properties of the device.
U.S. Pat. No. 5,505,985 to Nakamura et al. (Nakamura), discloses a process for depositing a film comprising an electrically insulating polymer as a protective layer on an outer surface of an organic electroluminescent device. Nakamura asserts that the polymers disclosed protect the device and have excellent electrical resistivity, breakdown strength and moisture resistance, while at the same time are transparent to emitted light. Nakamura also teaches that, when deposited by a physical vapor deposition (PVD) method, the protective layer formed by the polymer compound is pin-hole free. The sealing method taught by Nakamura, however, yields a moisture diffusivity too high to be useful for reliable OLEDs. Moisture levels as low as 1 ppm may damage an OLED.
Others have tried evaporated metal films to seal an OLED. However, to avoid pinholes, these films must be relatively thick, resulting in poor light transmission.
Hermetic sealings for OLEDs are the key to better performance. An epoxy-based sealing process, however, is not desirable because moisture permeation through the epoxy is significant. A metal seal process is the best solution to the problem. Although metal sealing provides the necessary hermeticity, the actual process of sealing, using a suitable solder material, poses many problems. The most significant problem is that of heating the substrate that contains the OLEDs during the sealing process. Since the OLEDs can not withstand exposure to more than about 120° C., it is difficult to obtain a good seal at such a temperature. A more rugged seal requires higher temperatures.
In the case of monochrome OLEDs, the sealing process may be achieved by seam sealing. The use of a metal flange with a clear glass window provides a good sealing process. However, in the case of color OLED devices, the window-glass consists of patterned color filters or color changing media material (CCM). These color patterns need to be precisely aligned with the OLED device on the silicon substrate and then sealed. Seam sealing does not lend itself to such precise boding accuracy. Thermal sealing, using a thermal head, can also be used. However, the heat generated during the seal is too high.
In the present invention, Applicants use a focused light beam, such as a laser beam, to provide an efficient and practical way to seal color OLEDs. The innovative sealing process of the present invention is efficient in thermal budget, uniform in applying pressure and provides a high packing density of the device per silicon wafer. To prevent heat damage, a glass chuck is used to position an array of inverted heat sinks, so that each OLED is aligned with an individual heat sink.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to provide an efficient process for sealing an OLED.
It is another object of the present invention to provide a rugged seal for an OLED.
It is still another object of the present invention to provide an apparatus for sealing an OLED.
It is yet another object of the present invention to provide an apparatus for sealing an OLED utilizing a solid state laser.
It is a further object of the present invention to provide an apparatus for orienting an OLED and seal assembly having high alignment accuracy.
Additional objects and advantages of the invention are set forth, in part in the description which follows and, in part, will be apparent to one of ordinary skill in the art from the description and/or from the practice of the invention.
SUMMARY OF THE INVENTION
In response to the foregoing challenge, Applicants have developed an innovative, efficient and rugged sealing assembly for sealing an OLED device on a substrate. The sealing assembly includes a cover assembly adapted to be positioned over the OLED device. The cover assembly includes a periphery. The cover assembly further includes a securing assembly for securing the cover assembly to the substrate. The securing assembly is located about the periphery of the cover assembly. The sealing assembly further includes an attachment assembly for attaching the securing assembly to the substrate. The attachment assembly is located o
Ghosh Amalkumar P.
Heller Christian M.
Liu Yachin
Zimmerman Steven M.
Bazerman & Drangel PC
eMagin Corporation
Evans Geoffrey S.
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