Nanowire transistors show potential in electronic devices

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Engineers have demonstrated 3D nanowire transistors by combining atoms of semiconductor materials into nanowires and structures on silicon surfaces, a development that could lead to more robust electronic devices.

The advance, by engineers at the University of California, Davis, is claimed to create opportunities for integrating other semiconductors, such as gallium nitride, on silicon substrates.

‘Silicon can’t do everything,’ said Saif Islam, professor of electrical and computer engineering at UC Davis. Circuits built on conventionally etched silicon have reached their lower size limit, which restricts operation speed and integration density. Additionally, conventional silicon circuits cannot function at temperatures above 250 degrees Celsius, or handle high power or voltages or optical applications.

According to UC Davis, the new technology could be used to build sensors that can operate under high temperatures, such as inside aircraft engines.

‘In the foreseeable future, society will be dependent on a variety of sensors and control systems that operate in extreme environments, such as motor vehicles, boats, airplanes, terrestrial oil and ore extraction, rockets, spacecraft, and bodily implants,’ Islam said in a statement.

Devices that include both silicon and non-silicon materials offer higher speeds and more robust performance. Conventional microcircuits are formed from etched layers of silicon and insulators, but it’s difficult to grow non-silicon materials as layers over silicon because of incompatibilities in crystal structure (or lattice mismatch) and differences in thermal properties.

Instead, Islam’s laboratory at UC Davis has created silicon wafers with nanopillars of materials such as gallium arsenide, gallium nitride or indium phosphide on them, and grown nanowire bridges between nanopillars.

‘We can’t grow films of these other materials on silicon, but we can grow them as nanowires,’ Islam said.

The researchers have made the nanowires operate as transistors, and combined them into more complex circuits as well as devices that are responsive to light. They have also developed techniques to control the number of nanowires, their physical characteristics and consistency.

Islam said the suspended structures have other advantages in that they are easier to cool and handle thermal expansion better than planar structures, a relevant issue when mismatched materials are combined in a transistor.

The technology also leverages the well-established technology for manufacturing silicon integrated circuits, instead of having to create an entirely new route for manufacturing and distribution, Islam said.

The work is described in a series of recent papers in the journals Advanced Materials, Applied Physics Letters and IEEE Transactions on Nanotechnology.