This work presents a study of photostriction-based optical actuation in bilayer cantilevers made of silicon and germanium thin-films and follows previous work in this area on silicon cantilevers. This experimental and theoretical study examines the role of the silicon-germanium heterojunction in optical actuation. It is shown that the germanium layer dominates the mechanical response of the device, which can be exploited to achieve enhanced optical actuation in cantilevers.
Photostriction-based all-optical actuation of silicon microcantilevers has been investigated through experimental characterization of structures fabricated on silicon-on-insulator substrates, and through numerical modeling and analysis of their semiconductor device and micromechanical characteristics. Since the pressure coefficient of the bandgap is negative in Si, photostriction-induced photoactuation in Si-based cantilevers was evident as upward mechanical defections (away from the substrate) in response to pulsed laser illumination on the cantilevers' top surface, which is in contrast to the downward deflections typical of photothermal effects. For the numerical modeling of photostriction induced effects, carrier lifetime and excess-carrier concentrations were determined from transient photoconductance measurements. The experimentally determined parameters were then employed to simulate carrier-density profiles across the modeled structure. The modeled cantilever deflections were found to be in excellent agreement with experimentally determined deflections. It is also shown that 100-µm-long Si cantilevers were deflected by up to 10 nm, and generated a force of 0.14 nN, when optically actuated by a 405-nm laser power density of 400 W/cm 2 .[2013-0348]
Abstract. A novel MEMS resonator employing "capacitance-shaping" principle to generate sinusoidal signals is proposed. FEM simulations are done to study the structure. Preliminary characterizations on devices fabricated through SOI-MUMPS are carried-out to study the frequency tuning of the resonator by electrostatic actuation. Variants of the proposed structure are presented. Second order dynamical models of the devices are derived.
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