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Sensors/MEMS??

Nanowires found useful in pressure sensors

Posted: 11 Apr 2012 ?? ?Print Version ?Bookmark and Share

Keywords:pressure sensor? piezoresistive material? field-effect transistor? nanowire?

Researchers from A*STAR Institute of Microelectronics have developed a nanowire-based sensor that according to them touts high sensitivity that it can detect even very low pressure changes. The discovery complements the far-reaching applications of miniaturized pressure sensors that include mechanical and biomedical devices.

The researchers indicated that most miniaturized pressure sensors harness the intrinsic properties of piezoresistive materials. A structural change in such a material, induced for example by an external force, results in a complementary change in its electrical resistance. However, piezoresistive materials have two major limitations. Firstly, these materials are not particularly sensitive, which means that low pressures produce weak electronic signals. Secondly, these materials can generate a lot of electrical noise, which can mask the true measurement signal. An ideal transducer should have a high signal-to-noise ratio (SNR). Woo-Tae Park and his co-workers have now used nanowires to create a pressure sensor with enhanced SNR properties.

Previous research has shown that nanowires can exhibit high piezoresistive effects because of their small size. To take advantage of this, Park and his co-workers used modern material processing techniques to suspend two silicon nanowires between two electrodes on a silicon-on-insulator substrate. Each wire was a few hundred nanometers long and about 10nm wide. They were covered in amorphous silicon that both protected them and acted as an electrical connection, referred to as the gate. The researchers attached to this a circular diaphragm: a two-layer membrane of silicon nitride and silicon dioxide. Any stress in the diaphragm was therefore transferred to the nanowire structure.

The team characterized their sensor by passing a controlled stream of air across it. Ammeters measured the current flowing through the device as a known electrical potential was applied across the two electrodes. An additional voltage, the gate bias, was also applied between one of the electrodes and the gate. Park and his co-workers demonstrated that they could achieve a four-fold increase in pressure sensitivity by reversing the direction of this gate bias. This, they believe, is a result of the bias voltage controlling the confinement of the electrons within the nanowire channelsa concept commonly used in so-called field-effect transistors (FETs). An assessment of the device noise characteristics also showed significant improvements with the right choice of operating parameters.

Park and his co-workers believe that the device provides a promising route for applications requiring miniaturized pressure sensors that use little power.





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