In the previous work a quasi-static MEMS mirror with a novel design and powerful piezoelectric driving material of AlScN was shown, which possesses large mechanical tilt angles of up to ±12.5°, high frequency of about 1 kHz, high fill-factor (aperture diameter is 0.8 mm and die size is 1.3 x 1.1 mm2), great long-term stability and great linearity. Further developments have been done for improving the material properties of AlScN, moreover, to integrate the mirror plate onto actuators by BEOL bonding process instead of hybrid assembly, since for the high fill-factor and good mechanical linearity the mirror plate and actuators are on different planes. Additionally, a third wafer of TSV wafer is used for the vertical electrical contacts. This unique technology includes not only triple-wafers-bonding, after which the wafer stacks also have to withstand grinding and pattering via DRIE. This paper shows the process efforts for realizing the triple-wafer-stack and discusses the technological challenges and also achieved results.
Presented here is the world’s first resonant 1D MEMS mirror achieving mechanical scanning angles exceeding ±45° and thus providing a field of view of up to 180°. The MEMS scanner features a 2 mm x 4 mm ellipsoid mirror plate and oscillates at a scan frequency of about 1.5 kHz. Integrated sensors and closed-loop control allow for an accurate position detection below 0.1°. To achieve the scan angles as well as to guarantee long lifetime and reliability, the MEMS mirror is hermetically sealed on wafer level by a dedicated glass cover and operated in vacuum.
This paper presents a new type of piezoelectric quasi-static mirror, which utilizes a three-level-construction comprising a mirror plate (diameter = 0.8 mm), a pillar and four actuators hidden beneath the mirror plate, reducing the chip size to 1.3 mm2 . Special folded springs connecting the pillar and actuators are applied to reduce the mechanical non-linearity. Moreover, the newly developed piezoelectric material AlScN delivers large force enabling a mechanical tilting angle of ±12.5° at 150 VDC, as well as benefits like great linearity, repeatability and long-term stability. No angle change larger than 0.02° was observed during 100 on-and-off switching circles with 5 s intervals under 100 VDC. Long-term test over 76 hours under 100 VDC has shown maximum 0.1°shift. More precise measurements are ongoing. Based on the great linearity a simple closed-loop-control has also been developed and more results will be presented in the near future.