A novel fabrication technology for anti-reflex wafer-level vacuum packaged microscanning mirrors

Abstract

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.