German breakthrough paves way to foldable flat-screen displays

A major barrier to the miniaturization of medical imaging devices from hand-carried ultrasound to pocket-size PACS may be folding ... literally.

Scientists at the Max Planck Institute for Solid State Research in Stuttgart, Germany, have devised the enabling technology for flat-screen displays that could be unfurled when needed, then tucked back into a jacket pocket.

The idea of using organic circuits for such flexible displays has been around for awhile. But its real-world progeny have gobbled too much energy to be feasible, quickly draining the batteries needed to make the mobile devices into which they would be plugged work.

Hagen Klauk, Ph.D., a research group leader at the institute, and colleagues have overcome this problem, creating organic electronics that draw voltages in line with those of normal household batteries, between 1.5 and 3 volts.

These transistors, made from organic materials, can be constructed on flexible surfaces such as plastic film, making organic circuits ideal for portable and mobile devices.

According to a paper in the February issue of the journal Nature, these energy-saving organic compounds can be deposited on a substrate in a layer less than 3 nanometers thick. Because the voltage needed to operate a circuit depends on the thickness of the monolayer coating the transistor's substrate, the use of such a thin monolayer cuts the necessary operating power.

The German researchers didn't stop there. They created a flat panel with complementary circuits involving two different transistor types that work together to organize the flow of signals.

"Complementary circuits have been standard in silicon technology for 25 years," Klauk said. "By combining them with self-organizing monolayers, we could lower the supply voltage to that of small batteries."

The end result, a flexible flat panel, is made possible by a nexus of these technologies. Silicon transistors rely on glass, Klauk said, because they need a substrate that can stand up to the high temperatures needed to make the transistors. Organic transistors, however, can be manufactured at temperatures below 100°C, paving the way for the use of plastic.

Just as a plastic substrate is essential to the development of a foldable flat panel, the use of organic electronics is essential to the use of plastic. The resulting organically based flat panels, therefore, are both flexible and sturdy - an ideal combination for technologies applied in healthcare.