A large-displacement CMOS micromachined thermal actuator with comb electrodes for capacitive 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. Capacitive sensing with vertical comb electrodes is used for detection of the actuator displacement. The microactuator is characterized by the static and dynamic measurements, showing a measured out-of-plane displacement of 24 μm at an applied power of 17 mW, a thermal time constant of 0.24 ms, and a mechanical resonant frequency at 16.8 kHz with a quality factor of 21. The measured minimum input-referred noise voltage of the sensing amplifier is 16.9 μV/Hz, equivalent to a minimum input-referred noise displacement of 0.34 nm/Hz at a displacement of 6 μm. The fabricated devices, after additional post micromachining, are intended for use as scanning cantilevers in atomic force microscopy.