PZT MEMS Actuator with Integrated Buried Piezoresistors for Position Control

We have monolithically integrated a PZT thin film and "buried" Si piezoresistive sensors for piezoelectric MEMS actuators. The PZT thin film works as a sensor as well as an actuator, but the static position sensing is difficult unlike piezoresistors. On the other hand, the process compatibility of PZT with a Si piezoresistor is unclear, because the Si piezoresistor is very sensitive to impurities, surface charges and contaminations. In this study, PZT MEMS cantilevers with the "buried" Si piezoresistive sensors were successfully fabricated by a proposed fabrication process, and the material composition was analyzed by secondary ion mass spectrometry (SIMS) to study the process compatibility. The fabricated devices were actuated by the PZT thin film, showing the first resonance frequency at 6.3 kHz. The integrated position sensor could successfully detect the amplitude with a sensitivity, non-linearity and noise floor of 0.037 mV/pm, 0.75% and 1 × 10-6 V/√Hz, respectively.