Early computational machines were constructued using mechanical levers and actuators, which were later replaced by electronic machines that were faster and more reliable. As the sizes of devices continue to shrink, however, moving mechanical parts have been reintroduced to achieve new functions. Modern nano- and micro-electromechanical systems now combine electrical and mechanical features to achieve a variety of functions, including sensing and communications.

Most nanoelectromechanical devices are made from silicon. However, mechanical silicon components tend to stick and break, making the devices unreliable at high temperatures or in extreme environments. Diamond is stiffer, harder and more resistant to corrosion, but it also suffers from poor reliability and reproducibility due to impurities and weaknesses on grain boundaries in the polycrystalline diamond materials used so far in such systems. Meiyong Liao and colleagues at the National Institute for Materials Science in Japan have now produced a nanoelectromechanical device made from single-crystal diamond that solves these problems.1

Fig. 1: A nanoelectromechanical switch made from single-crystal diamond. The cantilever is pulled or pushed to make or break contact between the source and drain electrodes.© 2010 Wiley-VCH

The research team grew a layer of conductive, boron-doped diamond onto an insulating diamond substrate, which was then patterned and etched to make cantilevers and bridges hundreds of nanometers wide and up to 16 μm in length. This diamond-on-diamond approach avoided the structural mismatch that occurs between diamond and a substrate of a different material. This approach also produces mechanical structures that lie parallel to the substrate and which are designed to move laterally, in contrast to most silicon devices, which are vertically oriented. Another benefit of this fabrication scheme is that many devices can be made at once — a central requirement for mass-production.

The fabricated diamond cantilever structures were made to move and switch between two contacts by applying a voltage to nearby electrodes. In addition to being resistant to sticking, the devices showed high ratios between on and off currents, were stable at high temperatures and could be produced with consistent performance characteristics. Furthermore, because of the high stiffness of diamond, the devices are capable of operating at high frequencies. “We can now produce various resonators and sensors with improved performance, and as single-crystal diamond technology improves and costs drop, diamond nanoelectromechanical devices may begin to compete with their silicon counterparts.”