An integrated sensor circuit that is based on nanowire arrays and combining light sensors with electronics made from different crystalline materials, has been developed by scientists at the Lawrence Berkeley Laboratory of the U.S. Department of Energy and the University of California at Berkeley [Fan et all., doi10.1073pnas.0801994105].
Being virtually one-dimensional and having well defined atomic composition, a nanowire is an ideal shape for use as a light detector. Sensor downgrading to the nanoscale has been shown to drastically enhance their sensitivity in a variety of materials and applications. However, electronics must be integrated on the same chip to make this a practical application but the two devices would normally be made from different materials, presenting fundamental difficulties.
At Berkeley, nanowires were used for both sensors and transistors and were grown, either on a roller for contact printing or on a substrate that could be slid away. This has the benefit of ‘combing’ the nanowires into one direction and aligning them for uniform performance. “Our integration of arrays of nanowires that perform separate functions and are made of heterogeneous substances — and doing this in a way that can be reproduced on a large scale in a controlled way — is a first,” says research team leader, Ali Javey.
Offering the best photo sensor performance, cadmium selenide nanowires were used as visible-light sensors while germanium core/silicon shell nanowires comprised the electronic component, amplifying the light-response current produced by the photo sensors by five orders of magnitude. The two materials were positioned at precise locations on the receiver substrate, the device pattern on a photoresist layer coated on the substrate, which was removed by acetone. Metal electrodes were deposited and each circuit represented a pixel when used for imaging.
With small variations, successful photo response was shown in 80% of the resulting circuits and improvements are thought readily achievable with optimized device fabrication and nanowire synthesis. “This work presents a route toward utilization of nanowire materials for integrated sensors;