Resonant biaxial 7-mm MEMS mirror for omnidirectional scanning

Low-cost automotive laser scanners for environmental perception are needed to enable the integration of advanced driver assistant systems into all automotive vehicle segments, which is a key to reduce the number of traffic accidents on roads. Within the scope of the European-funded project MiniFaros, partners from five different countries have been cooperating in developing a small-sized low-cost time-of-flight-based range sensor. An omnidirectional 360-deg laser scanning concept has been developed based on the combination of an omnidirectional lens and a biaxial large aperture MEMS mirror. The concept, design, fabrication, and first measurement results of a resonant biaxial 7-mm gimbal-less MEMS mirror that is electrostatically actuated by stacked vertical comb drives is described. Identical resonant frequencies of the two orthogonal axes are necessary to enable the required circle scanning capability. A tripod suspension was chosen, since it minimizes the frequency splitting of the two resonant axes. Low-mirror curvature is achieved by a thickness of the mirror of more than 500 pm. Hermetic wafer-level vacuum packaging of such large mirrors based on multiple wafer bonding has been developed to enable a large mechanical tilt angle of +/- 6.5 deg in each axis. Due to the large targeted tilt angle of +/- 15 deg and because of the MEMS mirror actuator having a diameter of 10 mm, a cavity depth of about 1.6 mm has been realized.