Demonstration and characterization of PZT thin-film sensors and actuators for meso- and micro-structures

Abstract

Recent development of next-generation medical devices, such as endoscopes and hearing aids, call for PZT (lead zirconate titanate oxide) thin-film sensors and actuators with thickness in the range of 1–30 μm to enhance actuation strength and sensor sensitivity. Currently, sol–gel derived PZT films often have thickness less than 0.2 μm per coating. Moreover, thermal stresses in the films limit the crack-free area to less than 1 mm 2. This paper has four specific goals. The first goal is to demonstrate an improved sol–gel process using rapid thermal annealing and a diluted sealant coating. The resulting thickness can reach 2 μm in three coatings with a crack-free area as large as 5 mm×5 mm . The second goal is to characterize piezoelectric properties of the fabricated PZT films experimentally. The resulting piezoelectric constant d 33 is 120 pC/N and the dielectric constant ranges from 200 to 400. The third goal is to demonstrate the use of the PZT thin film as a calibrated sensor. The specimen is a silicon cantilever ( 30 mm×7.5 mm×0.4 mm ) with a PZT thin film ( 4 mm×4 mm×1 μm ). Moreover, a tiny shaker excites the cantilever at the fixed end, and a charge amplifier detects the charge accumulated in the PZT film. In the meantime, a laser vibrometer measures the deflection of the cantilever at three points along the PZT film, from which the strain is calculated using Euler–Bernoulli beam theory. Comparison of the strain and the charge amplifier voltage determines the calibration constant of the PZT thin-film sensor. The last goal is to demonstrate the use of the PZT thin film as a powerful actuator through active vibration control. In experiments, a tiny bulk PZT patch is first glued to the silicon cantilever. A function generator drives the bulk PZT simulating a source of disturbance exciting the silicon cantilever. In the meantime, a laser Doppler vibrometer (LDV) measures velocity of the cantilever tip. With a phase shifter as the controller, the LDV measurement is fed back to the PZT thin-film actuator to actively control the cantilever vibration. To evaluate the effectiveness of the active vibration control, a spectrum analyzer measures the frequency response functions (FRF) from the bulk PZT voltage to the LDV response. Experimental results show that the simple active vibration control scheme can reduce resonance amplitude of the first bending mode by 66%.