Air Force Research Laboratory scientists have demonstrated world-record performance of transparent transistors created from thin-film nanocrystalline zinc oxide which can function, undetected, on clear surfaces such as glass or plastic.

Lead investigator Dr. Burhan Bayraktaroglu of AFRL's Sensors Directorate and his team are responsible for developing and testing these transparent transistors under support from the Air Force Office of Scientific Research.

A combination of high channel mobility, mechanical flexibility and high optical transparency at room temperature make the transparent transistors excellent candidates to support a wide range of future Air Force electronics needs and applications.

Dr. Kitt Reinhardt, the AFOSR program manager, said potential applications include: video image displays and coatings for windows, visors and windshields; electrical interconnects for future integrated multi-mode, remote sensing, focal plane arrays; high-speed microwave devices and circuits for telecommunications and radar transceivers; and semi-transparent, touch-sensitive screens for emerging multi-touch interface technologies.

Another attractive aspect of this new type of thin film transistor is that the processing technology used to fabricate the devices is relatively simple and is compatible with inexpensive plastic and flexible substrate technology.

The AFRL team found that the trick to controlling the conductivity and transparency of the devices is optimizing the size and density of the zinc oxide nanocrystals.

They have demonstrated films that are 90 to 95 percent transparent, have metal-like electrical conductivities and can withstand high temperatures for long periods without degrading.

Dr. Bayraktaroglu and his team have used these devices to demonstrate the world's first thin-film microwave transistor.

They also have perfected the application of zinc oxide films onto various surfaces using a special technique called pulsed laser deposition, which employs an ultraviolet laser beam to remove zinc oxide nanocrystals from a source, and deposit them as a thin film on the desired surface.

These films are then processed into field effect transistors and transparent conductors using standard lithography techniques.