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Optoelectronics/Displays??

Organic light source remembers its setting

Posted: 11 Feb 2002 ?? ?Print Version ?Bookmark and Share

Keywords:bistable organic light-emitting? ucla? organic bistable memory device? organic led?

US researchers have developed a bistable organic light-emitting device that could let displays double up as non-volatile memories.

Scientists in the department of materials science and engineering, University of California at Los Angeles (UCLA), have combined an organic bistable memory device (OBD) and a polymer LED to produce a non-volatile memory that can be read electrically or, thanks to the fact it glows, optically.

Dr Yang Yang, associate professor of materials science and engineering at UCLA, said: "This is a rather important invention for two reasons.

"First, we report an organic memory device with a performance that exceeds all existing memory devices. Second, we combine this organic memory with a light-emitting device and create another kind of memory light-emitting device."

By combining an OBD and an LED, the team demonstrated an organic bistable LED (OBLED) which can be addressed and stored electronically, and read out either electrically or optically by measuring the injection current or the light emission.

Dr Yang said: "I consider this invention [the organic bistable device] as important as the first organic LED paper published by Tang in 1987."

The scientists built a structure that consists of three layers between two electrodes. By using a voltage to bias it, the device can be switched from a high impedance state to a low impedance state.

The device remains in that state until another voltage, in reverse bias, is applied. The low- or high-impedance state remains even when the power is turned off.

A polymer LED is integrated into the device so that information can be read out optically.

Dr Yang explained the advantage of optical detection: "For traditional OBD memory devices having the X-Y matrix format, the reading of the memory array is usually in serial sequence?that is, the maximum data throughput is achieved by scanning one line after another.

"But the optical detection capability of OBLEDs enables parallel reading, which enhances the reading speed dramatically. The throughput of the memory array can become instant by turning on the whole memory array simultaneously."

Most important, due to the presence of electroluminescence, human eyes can read the recorded information directly.

Possible applications for the OBLEDs include digital memories, optoelectronic books, newspapers and smart papers.

The team's next steps will be to understand the mechanism of the device better, to reduce it to micron size and to demonstrate a 1Kbyte memory chip by the end of 2003.

? Sara Sowah

EE Times





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