Polymer transistors hint at all-organic displays

Researchers at Pennsylvania State University have built an active-matrix (AM) LCD that uses polymer transistors in place of silicon devices. The technique makes it possible to form LCDs on substrates that would not survive the temperatures needed for silicon-based displays.

The Penn State team claims the performance of the display is comparable to those built using amorphous silicon devices.

According to Thomas Jackson, professor of electrical engineering at Penn State, the same basic organic thin film transistor (TFT) technology could be used for cheap handheld or large-area displays.

“Organic TFTs could be combined with organic LEDs [OLEDs] to build an all-organic AM display because organic TFTs allow low processing temperatures and also very low-cost processing.

“They are also of interest for applications such as smartcards, RF ID tags and large-area sensors.”The Penn State team used a maximum processing temperature of about 110C for its display. Lower temperature processing may be possible. This means that electronics on polymers or even cloth or paper could be possible using techniques more akin to printing than conventional electronics fabrication.

“One can envision a facility that took a large roll of plastic and produced displays or other electronics in a continuous web process at a very low cost,” said Prof Jackson.

The next step will involve combining organic TFTs with OLEDs on a polymer substrate. The team has completed other work using organic and inorganic TFTs on polymers to make micro-electromechanical actuators.

Other groups working on similar projects include Lucent Technologies, IBM, 3M, Xerox, and Sarnoff in the United States, Plastic Logic in the United Kingdom and several Japanese and South Korean companies.

But plastics may not be the only way forward. Last year, U.S.-based Flexics said it had developed a process for polysilicon that does not need temperatures above 100C.

? Sara Sowah

EE Times