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.
A Georgia Tech research team has developed a new class of electronic logic device in which current is switched by an electric field generated by the application of mechanical strain to zinc oxide nanowires. (Photo credit: Gary Meek)
"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.
Georgia Tech researchers measure the performance
of an array of zinc oxide nanodevices fabricated on a flexible polymer
substrate. (Credit: Gary Meek)
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.
In a sense, strained-gate transistors are merely a reinterpretation of the piezoelectric nanowire--defining the wire as the transistor's channel and its bending as the gate to turn it on and off. But by demonstrating that logic circuits can be constructed using this reinterpretation, these researchers makes a strong case for defining a new field called piezotronics.
Interesting invention. I think more can be developed when it comes to sensing motions or energy harvesting. I wonder maybe one day this kind of technology can be implanted inside a living body so that computer can directly deal with our muscle contraction.
Thinking of strain gated switches on a nano scale, Bionics seems like a good area of application. Also, think with nanobots technology progressing rapidly, a mechanical interface to logic is a welcome step.
It sounds similar to what Nantero's carbon nanotubes base NRAM. The second half of the article is actually pretty interesting, think about it, the receptors in our eyes actually convert photons to mechanical energy to "touch" the nerve ends. There may be some applications in artificial vision.
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