SiGe micromirrors for optical applications

Micromirrors are a typical example of Micro-Electromechanical Systems (MEMS) with many applications including optical scanners, optical switching, projection displays, etc. We have succeeded in producing MEMS micromirrors in a SiGe structural layer, which can be used to realize CMOS-integrated MEMS structures. Several pixel designs were simulated using COMSOL multiphysics and subsequently verified in hardware. They differ in mirror size, hinge length and number of attracting electrodes (two or four). One particular mirror design enables variable Pulse Width Modulation (PWM) addressing. In this design, the mirror switches between two extreme states with a variable duty cycle determined by two generic high voltage signals and two CMOS-compatible pixel-specific DC voltages applied to the four attracting electrodes. The processed arrays were subjected to Laser Doppler Vibrometer (LDV) measurements in order to verify the simulation results. The simulated and measured pull-in voltages are compared for 8, 10 and 15µm mirrors. The agreement between simulation and measurement lies within the expectations, which is an encouraging result for future designs.Micromirrors are a typical example of Micro-Electromechanical Systems (MEMS) with many applications including optical scanners, optical switching, projection displays, etc. We have succeeded in producing MEMS micromirrors in a SiGe structural layer, which can be used to realize CMOS-integrated MEMS structures. Several pixel designs were simulated using COMSOL multiphysics and subsequently verified in hardware. They differ in mirror size, hinge length and number of attracting electrodes (two or four). One particular mirror design enables variable Pulse Width Modulation (PWM) addressing. In this design, the mirror switches between two extreme states with a variable duty cycle determined by two generic high voltage signals and two CMOS-compatible pixel-specific DC voltages applied to the four attracting electrodes. The processed arrays were subjected to Laser Doppler Vibrometer (LDV) measurements in order to verify the simulation results. The simulated and measured pull-in voltages are compared for 8, 10 and 15µm mirrors. The agreement between simulation and measurement lies within the expectations, which is an encouraging result for future designs.P