Silicone Oil Damping for Quasi-Static Micro Scanners with Electrostatic Staggered Vertical Comb Drives

Abstract

Many applications like image projection, distance sensors or spectroscopy require high speed quasi-static operating scanners with the size of several millimeters for the laser beam guidance. Quasi-static micro scanners with electrostatic staggered vertical comb drives of sizes up to 5 mm achieve remarkable mechanical deflections of +-8 degree and eigenfrequencies of several hundred Hertz. Closed-loop control of the scanner position highly reduces parasitic eigenfrequency oscillation when driving an arbitrary trajectory like triangle or saw tooth, but requires position feedback and high performant drive electronics for real-time control. In this contribution we investigate silicone oil to attenuate undesired oscillations by passive mechanic damping. We present experimental results with different viscosity and determine the resulting system parameters such as damping coefficient, eigenfrequency and permittivity, supported by transient simulations. While the permittivity, refractive index and damping increase significantly, the deceasing eigenfrequency results in slower admissible trajectories. The overall performance is assessed and compared to the active damping approach using closed-loop control of the micro scanner operating in air. Finally, a potential packaging technology is presented.