Waferlevel Vacuum Packaged Microscanners: A High Yield Fabrication Process for Mobile Applications
Keywords:microscanner, vacuum, waferbonding, quality factor, laserdisplay
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°.