New Thin-film Transistors Could Mean Flexible Screens

Ultra-thin, flexible transistors could lead to the next generation of screens for computers, smartphones and televisions.

A team from the U.S. Department of Energy’s Argonne National Lab has created transparent transistors 10 atomic layers thick. Traditional thin-film transistors are used for screens and displays, such as flat-screen TVs and smartphones; until now, however, such transistors have been able to produce only rigid displays.

“This (discovery) could make a transparent, nearly invisible screen,” said Andreas Roelofs, interim director of Argonne’s Center for Nanoscale Materials. “Imagine a normal window that doubles as a screen whenever you turn it on, for example.”

A scanning electron microscope image of the thin-film transistor. Courtesy of Saptarshi Das, Argonne National Lab.

The researchers used a strip of tape to remove a sheet of tungsten diselenide that was only a few atoms thick — a technique invented by scientists at the University of Manchester. Next, they used chemical deposition to grow sheets of other materials on top, allowing them to build the transistors layer by layer.

The transistors were found to maintain optimal performance in a wide range of temperatures (from -320 °F to 250 °F), the researchers said, which is a valuable property given how hot some electronics can run.

The on/off ratio of the transistors was then measured, as was the field effect carrier mobility, which measures how completely the electrons can move through.

“We were pleased to find that the on/off ratio is just as good as current commercial thin-film transistors,” said Saptarshi Das, lead researcher and postdoctoral scientist at Argonne. “But the mobility is a hundred times better than what is on the market today.”

The researchers also studied how the transistors acted under stress by bending the films. Existing thin-film transistor material would crack under such pressure. The new transistors’ properties did not change, Roelofs said. Instead, “the layers just slide.”

The team hopes to add logic and memory to the flexible films. This would allow for development of not only screens, but an entire flexible, transparent TV or computer.

The research is published in Nano Letters (doi: 10.1021/nl5009037).

For more information, visit www.science.energy.gov.