Piezotronics defines new semiconductor-device category

PORTLAND, Ore.—Piezotronic transistors harness the piezoelectric effect in zinc-oxide nanowires to transform mechanical motion into a signal that controls arithmetic—logic operations. Researchers at the Georgia Institute of Technology recently demonstrated their new breed of piezotronic circuits performing standard digital circuit functions.

Piezotronics marks a new class electronic device that uses a MEMS-like moving part to create an electric field which controls a field-effect transistors (FET). Its inventor, professor Zhong Lin Wang, claims that such strain-gated transistors work like a traditional FET—with the current flowing from source to drain being gated by an electric field--but the field is generated by bending a piezoelectric nanowire—called strain—rather than by storing charge on the gate. The resulting strain-gated transistor could have direct uses for nanobots, microfluidics and other applications of micro-electro-mechanical systems.

"This type of device allows mechanical action to be interfaced with electronics," said Wang "And could form the basis for a new kind of logic device that uses the piezoelectric potential in place of a gate voltage."

Wang's Georgia Tech research lab has been pursuing applications of semiconducting piezoelectric nanowires for several years. Each application he tried, however, required building up the circuitry from scratch. However, by establishing a set of standardized piezotronic circuits on inexpensive polymer substrates, the researchers hope to more quickly develop future applications in everything from sensing the pushing of a button to tracking fluid flows to clothing that generates energy from the motion of its wearer.

Circuits harnessing strain-gated piezoelectric transistors, which are both semiconducting and piezoelectric, were recently demonstrated by the team as capable of realizing standard logic functions including inverters, NOR, XOR and NAND gates as well as multiplexer and demultiplexer functions.

"This is the first time that a mechanical action has been used to create logic operations," said Wang.

Currently, the Georgia Tech team is experimenting with using lasers to control the conductivity of piezotronic devices by taking advantage of the photo-excitation properties of zinc-oxide interfaces with metal electrodes whereby ultraviolet light creates electron-hole pairs which alter the height of the Schottky barrier there. Used together, lasers and mechanical strain promise to provide fine-control over future "piezo-phototronic" devices. The group is also experimenting with combining carbon nanotubes with zinc-oxide nanowires to create hybrid devices.

Funding for the Georgia Tech project was provided by the National Science Foundation, the Defense Advanced Research Projects Agency and the U.S. Department of Energy. Wang's team consisted of researchers Wenzhuo Wu, Yaguang Wei, Youfan Hu, Weihua Liu, Minbaek Lee, Yan Zhang, Yanling Chang, Shu Xiang, Lei Ding, Jie Liu and Robert Snyder.