Rotary MEMS comb-drive actuator with large deflection for photonic applications

Rotary comb-drive electrostatic actuators with smooth vertical sidewalls were designed and fabricated for photonic applications. Silicon on insulator (SOI) wafers with device layer thicknesses of up to 100 μm and oxide layers of 1-2 μm were used. Structures were fabricated through bulk micromachining of the handle layer followed by removal of the buried oxide. Deep reactive ion etching (DRIE) of the device layer defined the comb structure with simultaneous release of the moving arm. Thick photoresist and oxide masking layers were used for the high aspect ratio deep etches. Notching effects or depth variations of device layers were not observed. Etch/ passivation cycles in DRIE were optimized to obtain smooth sidewalls. Traces of etch scallops were confined only to the first few microns of the top and bottom edges of the reflecting sidewall. A movable arm length of 2 mm with a maximum rotation of 2.8 degrees was achieved. The edge deflection was over 100 μm at 100 volts. The fabricated structure provides a long reflecting sidewall that is accessible for hybrid integration in three dimensional space. The fabricated structures can be reliably operated in the kilohertz range.