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  • Production-Scale Vapor-Phase Deposition Demonstrated for Organic LEDs

Photonics Spectra
May 2005
Richard Gaughan

Organic LEDs have intrinsic characteristics that make them promising for such applications as flat panel displays. They may enable displays that are lighter, thinner and use less electrical power than those based on liquid crystal, but they must also be inexpensive.

One driver of the cost of organic LEDs is the technique used to deposit the layers of materials in the manufacturing process. One technology that may reduce this cost is organic vapor-phase deposition, which proof-of-principle experiments have shown to be cleaner, more uniform and more efficient than the conventional vacuum thermal evaporation. Now manufacturing the LEDs with organic vapor-phase deposition has been demonstrated on a pilot production scale.

Theodore X. Zhou’s team at Universal Display Corp. in Ewing, N.J., in collaboration with Stephen R. Forrest’s group at Princeton University in Princeton, N.J., has developed a machine that incorporates both organic vapor-phase deposition and vacuum thermal evaporation capabilities for the fabrication of organic LEDs. Metallic layers are deposited in the high-temperature vacuum thermal evaporation chamber, and organic layers are deposited in the organic vapor-phase deposition chamber, which was designed and built in partnership with Aixtron AG of Aachen, Germany.

Using the system, the researchers manufacture green electrophosphorescent organic LEDs on glass substrates coated with indium tin oxide. Following deposition of a layer of copper phthalocyanine by vacuum thermal evaporation, the substrate is inverted in an integrated “flip chamber,” and four layers of organic compounds are deposited using organic vapor-phase deposition. After another inversion, LiF and Al layers are deposited in the vacuum thermal evaporation chamber again. The entire process takes place within the multichamber instrument, with no vacuum break until encapsulation.

With an external quantum efficiency of 7 percent at 1000 cd/m2, the performance of the organic LEDs is comparable to ones fabricated by vacuum thermal evaporation alone. The lifetime is similar to that of conventional emitters, displaying 83 percent of initial luminance after 1000 hours of normal operation, and better in accelerated lifetime tests. Increasing the deposition rate of the emission layer does not adversely affect performance, suggesting the potential of the method for high-throughput manufacturing.

Zhou characterized the demonstration of a long operational lifetime in organic LEDs fabricated by organic vapor-phase deposition as an important step in the acceptance of the technique by the manufacturing community.

Applied Physics Letters, Jan. 10, 2005, 021107.

liquid crystal
A type of material that possesses less geometrical regularity or order than normal solid crystals, and whose order varies in response to alterations in temperature and other quantities. Liquid crystals are characterized by phase varieties, including cholesteric, nematic and smectic. The optical properties of liquid crystals are familiar from their use in displays, known as LCDs.
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