US scientists have developed the first examples of logic gates (NAND, NOR and XOR gates) that can be switched simply by bending the substrate. The gates exploit the piezotronic effect; a combination of piezoelectric and semiconducting effects in zinc oxide nanowires.
Logic gates are important components for new technologies such as portable electronic devices, nanorobotics, and control of flow in microfluidic devices. Nanowires are popular for making these gates as they can conduct electricity and provide high sensitivity. However a logic gate generally consists of both an electrically responsive unit and an externally applied voltage. These systems are known as CMOS or complementary metal-oxide semiconductor gates.
Zhong Lin Wang and his group at Georgia Tech, Atlanta, have come up with a new kind of logic gate. Building on their previous work that established a so-called piezotronic effect, which is a combination of the piezoelectric and semiconducting effects found uniquely in zinc oxide, the group have produced strain-gated devices. Strain gating uses the strain induced in a surface when the surface is bent to create a piezoelectric potential, which the group then use as the voltage input for the logic gate. This means that the logic gate can be switched on or off simply by bending the substrate.
The logic gates produced in this way can be used to make NAND, NOR, and XOR gates, from which any combination of required outputs can be produced. Wang’s team claim that their gates are complementary to conventional CMOS logic gates as they can be used in different circumstances and have different properties; for example, with regards to speed and operating conditions.
Wang hopes that the new strain-gated piezotronic logic gates will become integral to future nano/microsystems and that they will be used in combination with nanowire-based sensors and generators that his team have also helped to develop, to give self-powered, entirely nanowire-based devices. He says “I expect that piezotronics will find application in technologies related to human-electronics interfacing, smart MEMS, nanorobotics, and touch-pad sensing and actuators”.
W. Z. Wu et al., Adv. Mater., DOI: 10.1002/adma.201001925