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

Hermetic wafer level packaging of optical MEMS scanning mirrors is essential for mass-market applications. It is the key to enable reliable low-cost mass producible scanning solutions. Vacuum packaging of resonant MEMS scanning mirrors widens the parameter range specifically with respect to scan angle and scan frequency. It also allows extending the utilizable range of mirror aperture size based on the fact that the energy of the high-Q oscillator can be effectively conserved and accumulated. But there are also some drawbacks associated with vacuum packaging. This paper discusses the different advantageous and disadvantageous aspects of vacuum packaging of MEMS scanning mirrors with respect to laser projection displays. Improved MEMS scanning mirror designs are being presented which focus on overcoming previous limitations. Finally an outlook is presented on the suitability of this technology for very large aperture scanning mirrors to be used in high power laser applications

A higher achievable scan speed and the capability to integrate two scan axes in a very compact device are fundamental advantages of MEMS scanning mirrors over conventional galvanometric scanners. There is a growing demand for biaxial high speed scanning systems complementing the rapid progress of high power lasers for enabling the development of new high throughput manufacturing processes. This paper presents concept, design, fabrication and test of biaxial large aperture MEMS scanning mirrors (LAMM) with aperture sizes up to 20 mm for use in high-power laser applications. To keep static and dynamic deformation of the mirror acceptably low all MEMS mirrors exhibit full substrate thickness of 725 μm. The LAMM-scanners are being vacuum packaged on wafer-level based on a stack of 4 wafers. Scanners with aperture sizes up to 12 mm are designed as a 4-DOF-oscillator with amplitude magnification applying electrostatic actuation for driving a motor-frame. As an example a 7-mm-scanner is presented that achieves an optical scan angle of 32 degrees at 3.2 kHz. LAMM-scanners with apertures sizes of 20 mm are designed as passive high-Q-resonators to be externally excited by low-cost electromagnetic or piezoelectric drives. Multi-layer dielectric coatings with a reflectivity higher than 99.9 % have enabled to apply cw-laser power loads of more than 600 W without damaging the MEMS mirror. Finally, a new excitation concept for resonant scanners is presented providing advantageous shaping of intensity profiles of projected laser patterns without modulating the laser. This is of interest in lighting applications such as automotive laser headlights

Typical applications for resonantly driven vacuum packaged MEMS scanners including laser projection displays require a feedback signal for closed-loop operation as well as high accuracy angle synchronization for data processing. A well known and widely used method is based on determining the angular velocity of the oscillating micromirror by measuring the time derivative of a capacitance. In this work we analyze a capacitive sensing approach that uses integrated vertical comb structures to synchronize the angular motion of a torsional micromirror oscillating in resonance. The investigated measurement method is implemented in a laser display that generates a video projection by scanning a RBG laser beam. As the 2D-micromirror performs sinusoidal oscillations on both perpendicular axes a continuously moving Lissajous pattern is projected. By measuring the displacement current due to an angular deflection of the movable comb structures an appropriate feedback signal for ac tuation and data synchronization is computed. In order to estimate the angular deflection and velocity a mathematical model of the capacitive sensing system is presented. In particular, the nonlinear characteristic of the capacitance as a function of the angle that is calculated using FEM analysis is approximated using cubic splines. Combining this nonlinear function with a dynamic model of the micromirror oscillation and the analog electronics a mathematical model of the capacitive measurement system is derived. To evaluate the proposed model numerical simulations are realized using MATLAB/Simulink and are compared to experimental measurements

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