Electromagnetic actuation and MOS-transistor sensing for CMOS-integrated micromechanical resonators

A combined actuation and deflection sensing technique employing electromagnetic actuation and piezoresistive MOS-transistor sensing for CMOS-integrated resonators has been developed. It is exemplified for a cantilever resonator with on-chip amplifier, but is broadly applicable to other resonator types. The high efficiency of electromagnetic actuation significantly reduces the required operation power and allows for the use in portable devices. The resonator can be operated in a self-oscillation mode with a minimum power consumption of 69 μW. The minimum Lorentz force necessary was found to be 43 nN. By use of stress-sensitive PMOS-transistors as active loads, the size of the piezoresistive Wheatstone bridge is significantly reduced compared to diffused piezoresistors. Thirdly, the post-processing sequence of the cantilever resonator has been optimized, so that only one photolithography step is necessary to release the whole mechanical structure to facilitate the fabrication and reduce fabrication costs.

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