A virtual pivot point MEMS rotary comb actuator for tunable laser applications

Rotary comb-drive electrostatic actuators with virtual pivotal point of rotation were designed and fabricated for their application in external cavity tunable lasers in Littman configuration. Silicon on insulator (SOI) wafers with device layer thickness of 50 mu m and buried oxide layer of 2 mu m were used. The structures were fabricated through bulk micromachining of the device layer followed by release of movable arms through wet etching. Six pairs of comb arms were used to symmetrically distribute electrostatic forces on an interconnected movable arm structure. The movable structure consisting of stiff truss connectors in arc shapes on inner and outer periphery was anchored through three beams. Actuation of the movable arms on a circular profile with a virtual pivotal point was achieved for the designed range of operation. A maximum rotation of +/- 1.5 degrees at 190 V was achieved. The dimensions of the movable arm are on the order of 1.2-1.5 mm. The actuators have a physical clearance of up to 2.8 mm from the device structure to the virtual pivot point. The sidewalls of the movable arms are accessible for optical applications. The geometrical configuration of the fabricated structures supports the stringent requirements of optical path alignments in external cavity lasers. The fabricated structures can be reliably operated in the kilohertz range.