Fabrication of sonic sensors using PZT thin film on Si diaphragm and cantilever

Micro sonic sensors with a high quality factor (Q-value) using piezoelectric diaphragm and cantilever have been developed for detecting a specific sonic wave which is emitted due to anomalous behavior of rotary machines such as turbines, motors and engines. A piezoelectric PbZr_0.52Ti_0.48O₃ thin film was prepared on a micromachined SOI wafer by sol-gel method. The dependence of the output voltage of the both diaphragm- and cantilever-sensors on the sonic frequency was examined. The both sensors were found to have resonant peaks in the frequency region over 5 kHz with a high Q-value (>100), and the typical sensitivity for the sonic wave at the resonant frequency was estimated to be 10 mV/Pa, which is comparable to that of a commercial bulk ceramics sensor.