Design optimization of an electrostatically driven Micro Scanning Mirror

A design optimization of the electrostatic ally driven ID Micro Scanning Mirror development at the Fraunhofer Institute of Microelectronical Circuits and Systems has been carried out. The improvements are based on the use of non-Manhatten shaped structures for the mirror plate and the driving electrode combs. Several new design variants have been fabricated, characterized and are compared with devices of the previous design comprising quadratic mirror plates. The advantage of lower inertial moment favours the circular and elliptic design of the mirror plate. The capacity variation has been increased significantly by a special arrangement of the driving electrode fingers. Especially, a comb with star shaped fingers allows us to enhance the capacity variation remarkably. The experimental characterization of the devices shows that the elliptic plate with star shaped electrode combs is the variant to favour when the application requires large deflection angles for a given driving voltage and characteristic frequency. This meets the theoretical based expectation although the experimentally determined damping factor of devices with this design is significantly larger than for design variants with elliptic mirror plate and parallel electrode fingers. Devices of the novel design achieve mechanical deflection angles of up to+14.0° at a driving voltage of 11 V at low oscillation frequency. In comparison to the previous design this is an increase of 35 %.