A Large-Displacement CMOS-Micromachined Thermal Actuator with Capacitive Position Sensing

In this paper, we present the design and characterization of a large-displacement thermal actuator fabricated in a conventional CMOS process. The thermally-driven microstructure is fabricated by two dry etching steps after the completion of CMOS. The structure contains multiple layers of metal, silicon dioxide, and polysilicon. To avoid drift caused by change of ambient temperature, we adopt a capacitive sensing scheme that uses vertically sensed comb electrodes with a nominal sensing capacitance of 40 fF. The microactuator is characterized by static and dynamic measurements, with a measured out-of-plane motion up to 24 mum at 17 mW, a thermal time constant of 0.24 ms, and a mechanical resonant frequency at 16.8 kHz. The measured minimum input-referred noise voltage of the sensing preamplifier is 5.9 muV/radicHz, equivalent to a minimum input-referred noise displacement of 0.16 nm/radicHz