Using extended BELST process in fabricating vertical comb actuator for optical application

Angular motion plays a crucial role in optical applications such as switching and scanning. The angular motion is available using electrostatic actuation such as parallel plate, lateral comb, and vertical comb. Among them the vertical comb actuator (VCA) is regarded as the most promising approach to provide large angular motion. Recently, the High-Aspect-Ratio Micromachining (HARM) process has demonstrated its importance in offering even larger angular motion as well as extremely large stiffness microstructures. However, these approaches may suffer from alignment and bonding problems. An improved HARM process, the BELST (Boron Etch-stop assisted Lateral Silicon Etching), using a [111] silicon wafer is proposed in this study to fabricate a vertical comb drive actuator. Moreover, a large yet stiff mirror and a thin torsional spring are also available through this process within three masks. Thus the optical performance is improved and the driving voltage is reduced.