New type of logic device uses piezoelectric effect

The Georgia Institute of Technology says the devices, which include transistors and diodes, could be used in nanometer-scale robotics, nano-electromechanical systems (nems), micro-electromechanical systems (mems) and microfluidic devices. According to the researchers, the mechanical action used to initiate the strain could be as simple as a push of a button, or be created by the flow of a liquid, stretching of muscles or the movement of a robotic component. In traditional field effect transistors, an electrical field switches ('gates') the flow of electrical current through a semiconductor. Instead of using an electrical signal, the new logic devices create the switching field by mechanically deforming zinc oxide nanowires. The deformation creates strain in the nanowires, generating an electric field through the piezoelectric effect, which creates electrical charge in certain crystalline materials when they are subjected to mechanical strain. "When we apply a strain to a nanowire placed across two metal electrodes, we create a field, which is strong enough to serve as the gating voltage," said Zhong Lin Wang, a Regents professor in the Georgia Tech School of Materials Science and Engineering. "This type of device would allow mechanical action to be interfaced with electronics, and could be the basis for a new form of logic device that uses the piezoelectric potential in place of a gate voltage." This class of nanometer-scale device is called piezotronics as it uses piezoelectric potential to tune and gate the charge transport process in semiconductors. The devices rely on the unique properties of zinc oxide nanostructures, which are both semiconducting and piezoelectric. According to Wang, the transistors and diodes could be combined into systems in which all components are based on the same zinc oxide material. "The family of devices we have developed can be joined together to create self powered, autonomous and intelligent nanoscale systems. We can create complex systems totally based on zinc oxide nanowires that have memory, processing, and sensing capabilities powered by electrical energy scavenged from the environment." Using strain gated transistors fabricated on a flexible polymer substrate, the researchers claim to have demonstrated basic logic operations and multiplexer/demultiplexer functions by applying different types of strain to the zinc oxide nanowires. They also created an inverter by placing strain gated transistors on both sides of a flexible substrate. "Our work with strain gated devices provides a new approach to logic operations that performs mechanical-electrical actions in one structural unit using a single material," Wang concluded. "These transistors could provide new processing and memory capabilities in very small and portable devices."