Micro vertical comb actuators by selective stiction process

Selective stiction has been successfully applied to the batch fabrication of angular vertical comb actuators made of single-crystal silicon with self-aligned comb sets. The possible failure modes of the devices during the manufacturing process are studied, and a novel design of stiction plate and mechanical spring is also presented to suppress the failure modes. The fabrication process with unique designs of mechanical springs enables the stiction of microstructures in a controlled manner and significantly reduces unwanted compliances on the actuators, preventing unwarranted motion and providing stable operations. The prototype microactuators operate at a resonant frequency of 0.92 kHz with 85° optical scanning angle and quality factor of 162 in air under driving voltages of 19 Vdc plus 15 Vpp. A reliability test on an unpackaged actuator with more than 800 million cycles of operation showed extremely small variation in the resonant frequency and scanning angle, showing no sign of degradation in the induced stiction interface or the microstructures. Applications include scanning micromirrors, optical switches, and variable capacitors and we present results obtained with MEMS scanning mirrors.