Number 363 (Story #1), March 23, 1998 by Phillip F. Schewe and Ben Stein|
NANO-ELECTROMECHANICAL SYSTEMS (NEMS) will be faster, smaller, and more energy efficient than the present day micro-electromechanical systems (MEMS), an example of which is the accelerometer that triggers airbags in cars. At last week's American Physical Society meeting in Los Angeles, Michael Roukes of Caltech (626-395-2916) described the leading edge of NEMS research. Using lithography and etching techniques, the Caltech researchers (which include Axel Scherer, firstname.lastname@example.org) has fabricated a 10x10x100-nm suspended beam of gallium arsenide which oscillates at an estimated frequency of 7 GHz (although no detector can yet "hear" the vibrations). Such a resonator will eventually be used in microwave signal processing (for modulating or filtering signals). The speed and stability of nanoscopic silicon arms might even facilitate the advent of some new kind of Babbage-type computer in which mechanical levers once again serve as processing or memory elements.(In other words, a machine with "moving parts" may not be so bad.) Silicon structures in this size regime will also be used as cantilever probes in magnetic resonance force microscopy (the goal being atomic-resolution NMR imaging; see Update 313) and as calorimeters for the study of quantized heat pulses (Update 320). Roukes' colleague, Andrew Cleland of UC Santa Barbara, described a paddle-shaped silicon structure (whose smallest lateral feature was 200 nm) for detecting very small amounts of electrical charge, with a potential application in high- sensitivity photodetection (see also Nature, 12 March 1998). At the same APS session, Rex Beck of Harvard reported a NEMS force sensor which integrates a field effect transistor into a scanned probe microscope. The present sensitivities are about 10 angstroms for displacement and 5 pico-Newtons for force (per square root of the frequency), but Beck expects improvements as the size of the device shrinks. The smallest transistor-probe structure Beck reported had dimensions of 3x2 microns x 140 nm.