MEMS scanning micromirrors with a new electrostatic angular vertical combdrive

Details of the design, fabrication, and performance of two large area (1 mm diameter), microelectromechanical systems (MEMS) electrostatic scanners developed for optical switching and imaging applications will be presented. The development of a state-of-the-art scanning micromirror with novel angular vertical combdrive (AVC) actuation will be described. A complete silicon-on-insulator (SOI)-MEMS fabrication process has been developed at UCLA for realization of the AVC scanner featuring: deep reactive ion etching (DRIE) of a single commercial SOI wafer with no wafer bonding required. The moving and fixed fingers of the combdrive are self-aligned as they are formed with a single etch of the silicon device and subsequently rotated out of the wafer plane with a self-assembly technique based on polymer reflow. The polymer reflow with photoresist is found to be limited by residue in the high aspect ratio (23 to 25 μm thick with 3 μm gaps) structures formed by the combs and negative photoactive benzocyclobutene (BCB) is shown to eliminate this limitation. Static mechanical scan ranges of 14° at 65 V and 16.6° at 45 V have been achieved on AVC scanners with resonant frequencies of 598 Hz and 340 Hz, respectively. The measured static characteristics of the AVC scanners verify the numerical model utilized in designing the device. The development of a parallel-plate type scanner which employs a lightweight single crystal silicon honeycomb micromirror integrated with a surface-micromachined 2D scanner for improved flatness, compared to polysilicon alone, and improved response, compared to a solid bonded single crystal micromirror is also described.