Scanning laser projection using resonant actuated MEMS scanning mirrors is expected to overcome the current limitation of small display size of mobile devices like cell phones, digital cameras and PDAs. Recent progress in the development of compact modulated RGB laser sources enables to set up very small laser projection systems that become attractive not only for consumer products but also for automotive applications like head-up and dash-board displays. Within the last years continuous progress was made in increasing MEMS scanner performance. However, only little is reported on how mass-produceability of these devices and stable functionality even under harsh environmental conditions can be guaranteed. Automotive application requires stable MEMS scanner operation over a wide temperature range from -40° to +85°Celsius. Therefore, hermetic packaging of electrostatically actuated MEMS scanning mirrors becomes essential to protect the sensitive device against particle contamination and condensing moisture. This paper reports on design, fabrication and test of a resonant actuated two-dimensional micro scanning mirror that is hermetically sealed on wafer level. With resonant frequencies of 30kHz and 1kHz, an achievable Theta-D-product of 13mm.deg and low dynamic deformation <20nm RMS it targets Lissajous projection with SVGA-resolution. Inevitable reflexes at the vacuum package surface can be seperated from the projection field by permanent inclination of the micromirror

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Packaging of MEMS is an important expense factor within the production costs and, to ensure mass producibility, the packaging has to be performed on a waferlevel. While for inertial MEMS this is state of the art, it has not yet been reported for scanning micromirrors. Therefore, Fraunhofer ISIT has developed a process technology based on two 30 μm thick epitaxially deposited polysilicon layers for the manufacturing of waferlevel vacuum packaged MEMS scanning mirrors. It allows the fabrication of vertically stacked combdrives for out-of-plane mirror operation and a low damping environment for the reduction of needed driving signals. An anodically bonded structured glass wafer seals the devices at the front side, while an Au-Si eutectically bonded silicon wafer with an integrated 400 nm thick Ti getter layer is used to seal the devices from the backside. The measurement of the quality factor allows the estimation of the internal cavity pressure of sealed devices, which is in the range of 10-3 mbar.Waferlevel measurements showed that the fabrication process reaches a high mechanical yield of Ym = 95%. Vacuum packaged devices needed 6V driving voltage to reach a total optical scan angle of above 50°.

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The use of microscanning mirrors in mobile laser projection systems demands for robust fabrication technologies. Dust, change in humidity and temperature can only be tolerated if the fragile devices are enclosed in a hermetic package. A novel fabrication process is presented based on two 30 micron thick epitaxially deposited silicon layers and a buried interconnection layer. This technology allows the fabrication of stacked combdrives for electrostatic mirror actuation and lateral feedthroughs needed for hermetic encapsulation with standard wafer bonding processes. High display resolution requires large scan angles of the mirror plate. Therefore, a fabrication technology for structured glass wafers is presented to provide deep cavities for large mirror plate movements. A solution for effective laser spot reflex suppression is presented based on a static tilt of the mirror plate in relation to the glass cover wafer during eutectic bonding. By doing so, the reflex generated at the glass surfaces is shifted out of the image area. The cavity pressure of packaged devices has been measured showing the necessity of a getter layer in order to provide cavity pressures below 1 mbar. The performance of a packaged device with integrated getter layer has been evaluated. A driving amplitude of only 6 V is needed to achieve scan angles of above 50 deg. White light interferometric measurements showed excellent planarity of the mirror plate with a radius of curvature of about 18 m