To form practical nanotech circuits from arrays of nanowires, it is necessary to integrate different types of nanowires into multifunctional circuits. Two different types of nanowires (cadmium selenide for light sensors and germanium core/silicon shell for field-effect transistors) have been integrated on a chip to detect and amplify optical signals. From Lawrence Berkeley National Laboratory (credit PhysOrg.com) “A First in Integrated Nanowire Sensor Circuitry“:
Scientists at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory and the University of California at Berkeley have created the world’s first all-integrated sensor circuit based on nanowire arrays, combining light sensors and electronics made of different crystalline materials. Their method can be used to reproduce numerous such devices with high uniformity.
Nanostructures made with specific chemical, electronic, and other properties have a number of advantages over the same materials in bulk. For example, a nanowire is an ideal shape for a light detector; being virtually one-dimensional, practically “all surface,” a nanowire is not only highly sensitive to light energy, but its electronic response is greatly enhanced as well.
To be practical, however, the photosensors must be integrated with electronics on the same chip. And the materials that make an ideal photosensor are necessarily different from those that make a good transistor.
“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 Ali Javey, who led the research team. Javey is a staff scientist in Berkeley Lab’s Materials Sciences Division (MSD) and an assistant professor in the Electrical Engineering and Computer Sciences Department at UC Berkeley. He and his colleagues report their work in the August 1 edition of Proceedings of the National Academy of Sciences [abstract].
…Results of the Javey group’s integrated nanowire circuit showed successful photoresponse in 80 percent of the circuits, with fairly small variations among them. Where circuits did fail, the causes were due to defects in fabrication of the circuit connections (10 percent), failure in photosensor printing (5 percent), or defective nanowires (5 percent). The relatively high yield of complex operational circuits proved the potential of the technology, with improvements readily achievable by optimizing nanowire synthesis and fabrication of the devices.
“In the future, we can foresee using a variety of different optical sensors to create nanoscale devices sensitive to multiple colors in high-resolution,” says Javey. “And that’s just the beginning. We contemplate printing nanowire sensor circuitry — photosensors, chemical sensors, biosensors — not on silicon but on paper or plastic tape. This could be used, easily and with instant results, where spills have occurred, or to test air quality, or to test for disease organisms — almost any use for a sensor that you can imagine.”