High Stroke and High Deflection Bulk-PZT Diaphragm and Cantilever Micro Actuators and Effect of Pre-Stress on Device Performance

This paper presents the design, simulation, fabrication, and experimental characterization of high-performance piezoelectric diaphragm and cantilever beam out-of-plane micro actuators that are fabricated from bulk lead zirconium titanate (PZT) films integrated on silicon. The utilized fabrication technology involves low-temperature diffusion solder bonding of a bulk piezoelectric ceramic on silicon, and subsequent lapping to achieve a desired PZT thickness. Different piezoelectric actuation modes (conventional longitudinal and transverse modes, and a novel shear mode) are explored and compared in terms of displacement range, and the diaphragm structures and electrodes are optimized via finite-element analysis (FEA). The effect of bonding prestress on the device performance is analytically characterized and verified through measurements. The close match between test data and simulation results suggests that the piezoelectric properties of integrated bulk-PZT5A films are mostly preserved without any necessity of re-polarization. Fabricated devices are tested for dynamic displacement range, power consumption, and temperature response, and FEA is used to evaluate the actuation forces. A 25- μm thick 1- mm² sized diaphragm can provide 12 μmPP displacement at 111 kHz with power consumption, while 1-3.5 mm long cantilever beams of similar thickness provide 0.1-1 mmPP displacement at resonance frequencies of 0.7-7.4 kHz. The introduced devices can be leveraged in various ultrasonic and acoustic applications.