The BELST II process for a silicon high-aspect-ratio micromaching vertical comb actuator and its applications

Abstract

The BELST process has been proposed and it has demonstrated the capability to overcome anchoring and depth controlling issues in many high-aspect-ratio micromaching (HARM) processes. However, the actuation mechanisms are still restricted to in-plane motion only. In this study, a novel fabrication process called BELST II has successfully been developed. Moreover, the BELST II process was employed to fabricate a novel electrostatic vertical comb actuator (VCA). Three advantages for this VCA can be observed. First, through some exquisite designs the fabrication process has no critical alignment and bonding problems. Secondly, the relative vertical position between the moving and the stationary fingers can be adjusted freely to optimize the performance of the VCA. Thirdly, both a large mirror structure and trimmed torsional spring are available through this process. Thus, improved performance regarding enlarged traveling distance with reduced driving voltage can be obtained. In the application of the BELST II process, various HARM devices were realized, such as an optical scanner mirror and variable optical attenuator driven by the VCA.