Fabrication and performance of d₃₃-mode lead-zirconate-titanate (PZT) MEMS accelerometers

Piezoelectric accelerometers fabricated from Lead-Zirconate-Titanate (PZT) thin films are expected to achieve higher sensitivities and better signal-to-noise ratios (SNR) in comparison with capacitive and piezoresistive accelerometers. This paper will present, for the first time, the fabrication and performance of piezoelectric, bulk-micromachined accelerometers using PZT thin films operating in the d₃₃-mode. Using sol-gel techniques, 0.6μm thick PZT films with high piezoelectric coefficients were deposited. Measurements on these PZT films show a remnant polarization P_r > 19 μC/cm², dielectric constants ε_r > 800, and d₃₃ coefficient of 120 _pC/N. The PZT accelerometers operating in the d₃₃ mode were successfully fabricated. Interdigitated capacitors were used to achieve the d₃₃ mode of operation and deep reactive ion etching was used to define the proof-mass of the accelerometers. Measurements on these accelerometers show sensitivities ranging from 0.85-1.67 mV/g with resonance frequencies ranging from 22.4-15.4 kHz respectively. In addition to the improved sensitivity, advantages of d₃₃-mode accelerometers include use of thinner PZT films, and the ability to optimize the impedance of the device to achieve a higher SNR. The performance of MEMS d₃₃-mode accelerometers will also be compare with the previously reported d₃₁-mode accelerometers using PZT thin films.