Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
1999-11-05
2001-04-10
Crispino, Richard (Department: 1734)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S230000, C156S247000, C427S146000, C427S147000, C427S148000, C428S690000, C428S914000, C428S917000, C430S200000, C430S202000, C430S252000, C430S311000, C313S504000, C313S505000, C313S506000
Reexamination Certificate
active
06214151
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to processes for preparing opto-electronic devices, and more particularly relates to a thermal dye transfer process and its use in the manufacture of optoelectronic devices such as organic light-emitting diodes.
BACKGROUND
Organic light-emitting diodes (“OLEDs”) have demonstrated potential for applications in flat-panel displays due to the OLEDs' high luminescent efficiency, low driving voltage, large viewing angle, light weight, simple device fabrication, and potential low cost. See generally, U.S. Pat. No. 5,707,745 to Forrest et al. A typical OLED structure comprises one or more layers of organic materials sandwiched between a transparent anode such as a thin film of indium tin oxide (“ITO”) on a glass substrate and a metal cathode. When a direct current is applied between the anode and the cathode, holes and electrons are injected in the organic layers from the anode and cathode, respectively, and radiatively recombine, emitting light. Such an OLED structure and method of forming thereof are disclosed in PCT Publication No. WO 97/48139, directed to OLED structures and methods that allow for multiple colors to be integrated into a single substrate.
For color displays, red, green and blue emitters or “pixels” are typically required. Because of the size of the pixels in high resolution screens, it is impractical to deposit individual OLED pixels on a surface. However, the emission color of OLEDs can be changed through the incorporation of relatively small quantities of luminescent dyes into the host organic layers containing light-emitting materials. Therefore, closely positioned yet distinctly colored light emitters may be patterned by depositing a continuous layer of an OLED material on a surface followed by precise positioning and imparting small amounts of differently colored dyes to the layer. In other words, the color of an OLED display can be locally “tuned” by patterning the dye material without disturbing the OLED material. This concept has been demonstrated by introducing luminescent dyes locally using inkjet printing techniques. See, e.g., Hebner et al. (1998) Appl. Phys. Lett. 73: 1775-77. However, inkjet printing and other methods in which a separate dye droplet has to be applied for each individual pixel will limit the manufacturing rate of such displays. In addition, organic materials do not generally withstand conventional photolithographic processing in which solvents are used.
Thus, an improved method of introducing a dye pattern into an organic thin film over a large area, without resorting to sequential introduction of color into each individual pixel, is clearly desirable. One such method of patterning involves a hybrid stamp structure as described in U.S. Pat. No. 5,817,242 to Biebuyck et al. This patent describes a stamp is where a patterned layer is provided that can easily adhere or absorb a specific ink. If the ink contains an organic solvent, the stamp containing the solvent-based ink cannot be used to transfer the ink on to a receiving layer that may be adversely affected by the solvent.
Another method of introducing a dye pattern to an organic thin film over a large area is described in Pschenitzka et al. (1999), “Three-Color Organic Light-Emitting Diodes Patterned by Masked Dye Diffusion,”
Appl. Phys. Lett.
74: 1913-15. This reference describes diffusion by using a large area dye-doped polymer layer as the diffusion source. A patterned masking layer is sandwiched between the dye source plate and a substrate containing the receiving layer for OLED fabrication. By applying heat, the dye vaporizes or sublimes and thus deposits on and diffuses into the receiving layer in the desired pattern.
However, this thermal transfer method suffers from two main drawbacks. First, to effect dye transfer, the diffusion source must be heated to at least the vaporization or sublimation temperature of the dye. Because the dye source plate is in physical contact with a patterned mask which, in turn, is in contact with the film, thermal conduction would likely result in the receiving layer being heated to roughly the temperature of the diffusion source. Such excess heating will alter the microstructure or morphology of the film and may even damage the film. In particular, if the film already contains another dye pattern, that dye pattern will migrate due to elevated processing temperature and thus compromise the resolution of the final product. Second, because the mask necessarily has a thickness, the resulting resolution of the deposited dye pattern is further limited due to geometrical limitations on vapor transport from the dye source to the film.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the invention to provide a process for imparting a dye pattern into a receiving layer of a substrate as in the manufacture of opto-electronic devices including OLEDs, which process overcomes the above-mentioned disadvantages in the art.
It is another object of the invention to provide such a process wherein the dye pattern is imparted into a receiving layer of a substrate at a temperature that is no greater than the vaporization or sublimation temperature of the dye.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention.
In one aspect, the invention comprises a method for imparting a dye pattern into a receiving layer, the method comprising: (a) providing a substrate having a receiving layer thereon wherein the receiving layer comprises a light-emitting material; (b) providing a first dye transfer plate having a first dye composition on a first dye transfer surface thereof in the form of a first pattern, wherein the first dye composition contains a first dye; (c) bringing the first dye transfer plate and the substrate together such that the receiving layer and the dye transfer surface are in contact; and (d) heating the first dye transfer plate and the receiving layer to a first temperature to effect diffusion of the first dye into the receiving layer. Preferably, the method further comprises repeating steps (a) through (d) with a differently colored luminescent dye. It is also preferred that the dye transfer plate be compliant and for a conformal contact the the receiving layer and that the temperature used to effect diffusion of dye into the receiving layer not exceed the vaporization or sublimation temperature of the dye, in order to avoid compromising the resolution of the dye pattern formed in the receiving layer.
A particularly preferred use of the aforementioned method is in a color pixelation process for preparing an organic light-emitting diode. In such a case, the diode comprises a patterned, colored receiving layer formed by the aforementioned method sandwiched between first and second electrodes. The substrate can serve as the first electrode if the substrate is an electrically conductive material. Otherwise, the substrate further includes an electrode layer comprising an electrically conductive material wherein the first electrode layer is interposed between the substrate and the receiving layer. Optionally, hole-transporting or electron-transporting layers can be deposited between the first or second electrodes and the receiving layer. When holes and electrons are injected into the receiving layer by passing current through the electrodes, light is emitted thus forming a diode. Preferably, either the substrate and its electrode layer or the other electrode are optically transparent to transmission of the emitted light therethrough for opto-electronic applications.
In another aspect of the invention, an apparatus is provided for imparting a dye pattern into a receiving layer present on a substrate surface, i.e., for carrying out the above-described method. The apparatus comprises: (a) a first dye transfer plate having a first dye composition thereon in a first pattern wherein the compos
Chen Jianping
Salem Jesse Richard
Scott John Campbell
Crispino Richard
International Business Machines - Corporation
Lorengo J. A.
Reed & Associates
Wu Louis L.
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