Micro-Origami Fabricated Micromirrors

Microelectromechanical systems (MEMS) are becoming increasingly important as researchers develop miniaturized mechanical devices for communications, biotechnology, and a variety of measurement applications. Often these machines include hinged parts that must be set in place before operation, which can lead to challenging and time consuming manual manipulation of components at ever decreasing scales. Recently, researchers from the ATR Adaptive Communications Research Laboratories in Japan proposed a technique that they call micro-origami to fabricate MEMS devices that automatically move into position. The group has now tested the technique, in collaboration with researchers at Konan University and Osaka City University, by creating hinged micromirrors that lift themselves up following the final fabrication stage. The key to the micro-origami technique is to manufacture hinges out of a pair of material layers with slightly different atomic spacings. This lattice mismatch causes a stress that in turn bends the hinge (see figure) and, in this case, raises a mirror above the substrate. (The effect is reminiscent of the bimetallic strips in some thermostats, which consist of bonded layers of metals that expand at different rates when heated, leading to stresses that bend the strips as temperatures change.) Once a mirror was in place, the researchers could move it on its hinge by illuminating the mirror with a high power argon laser. It is not yet entirely clear what mechanism caused the illuminated mirror to move; the force due to radiation pressure, in particular, was too small and in the wrong direction to account for the effect. Nevertheless, the researchers (Jose M. Zanardi Ocampo, 81-774-95-1582) were able to use the motion of the micromirror to control the position of a reflected helium-neon laser beam. Potentially, the micro-origami mirror could lead to optical MEMS switches or other small devices that automatically pop into place without human or mechanical intervention, dramatically speeding and simplifying construction of miniature machines. (J. M. Zanardi Ocampo et al., Applied Physics Letters, 3 November 2003)