The effects of electrodes patterned onto the piezoelectric thin film on frequency response characteristics of PMN-PT MEMS acoustic actuators

摘要

The piezoelectric acoustic actuators were fabricated with PMN-PT single crystal membranes patterned by circular inter-digitated electrodes (IDEs) using silicon-based microelectromechanical systems (MEMS) technology. In order to investigate the effect of the electrodes patterned onto the PMN-PT membrane on the performance of the fabricated piezoelectric MEMS acoustic actuators, we simulated and analyzed the vibrational frequency response characteristics of the PMN-PT acoustic actuators with three different electrode diameters of 4, 6 and 8 mm. The PMN-PT piezoelectric acoustic actuators had a dimension of 11.7 x 11.7 mm(2), and the 10 mu m-thick and 8.5 mm-diameter PMN-PT membranes were formed by the backside etching process using both KOH silicon wet etching and Deep RIE equipment. From the simulated and measured results, it was shown that the vibrational displacement of the PMN-PT MEMS acoustic actuator can be improved with increasing area of the IDE patterned on the piezoelectric membrane. Moreover, the output sound pressure levels (SPLs) of the fabricated PMN-PT MEMS acoustic actuators were also improved with increasing areas of electrodes patterned on the piezoelectric membranes. Particularly, in a low-frequency range of less than 1 kHz, the PMN-PT piezoelectric MEMS acoustic actuator with an electrode diameter of 8 mm generated about 15 dB higher sound pressures compared to the piezoelectric acoustic actuator with an electrode diameter of 4 mm. These results reveal that not only the displacement characteristics but also the output sound performance of the PMN-PT MEMS acoustic actuator can be improved with increasing area of IDE patterned on the d(33) mode piezoelectric membrane.