Measurement of wear in polysilicon micromotors

Two polysilicon variable-capacitance rotary side-drive micromotor types, including harmonic and salient-pole, are described. Voltages as low as 26 and 35 V across 1.5-μm gaps are sufficient for operating the harmonic and salient-pole side-drive micromotors, respectively. Extended operation of the harmonic micromotors to near 100 million wobble cycles is studied at excitation frequencies of 10000 and 25000 r/min for operational durations of 150 and 71 h, respectively. The results of in situ quantitative studies indicate that, with micromotor operation, the rotor inner radius asperities wear out and the bearing clearance increases. This bearing wear is significant and results in changes in the gear ratio of the harmonic micromotors by as much as 22%. Typical gear ratios are near 90 at the start of harmonic micromotor operation and decrease to near 70 as the bearings wear out. For the salient-pole micromotors, wear particles are observed to form in the bearing and at the bushings. These wear particles adhere to the bushing surfaces and the area near the edge of the rotor inner radius