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This paper is to demonstrate a temporary encapsulating technique that uses photoresist to package PZT thin-film microactuators for an experimental inner ear implant. The microactuator consists of a diaphragm suspension, a bottom electrode, a PZT thin film, and a top electrode. The dimensions of the microactuator and the diaphragm suspension are 3 mm × 3 mm × 400 μ m and 900 μ m × 900 μ m × 0.95 μ m, respectively. A layer of photoresist (AZ1512) with a thickness around 4-16 μ m is brushed over the diaphragm suspension as the packaging material. The advantage of this temporary packaging technique is twofold. First, it does not substantially increase the size of the PZT thin-film microactuators. Second, it is waterproof thus allowing the microactuators to function in aqueous environments. To evaluate how the temporary package affects the performance of the microactuator, a function generator drives the microactuator at 1, 3, 5, and 10 kHz and a laser vibrometer measures the vibration of the diaphragm suspension before and after the microactuator is packaged. Experimental measurements show that the presence of the package reduces the gain of the microactuator from 0.33 nm/V to 0.15 nm/V. Also, an impedance analyzer measures the impedance of the packaged microactuator, while it is driven in air and in water. The measured impedance shows no difference in air and in water. This indicates that the temporary package is waterproof and the actuator is strong enough to function in an aqueous environment. [ABSTRACT FROM AUTHOR]

This paper consists of three major topics. The first topic is a review of challenges encountered in PZT thin film fabrication. Currently, sol-gel processing is one of the most promising techniques to fabricate PZT thin films. There are, however, several major challenges, including crack formation, thermally unstable electrodes, and poor piezoelectric properties. The second topic reveals some innovative fabrication processes that could substantially enhance quality of PZT thin films. For example, use of dilute sealant layer and rapid thermal annealing can lead to PZT films with large crack-free area. Use of sol electrophoretic deposition can enhance piezoelectric properties and thickness of PZT films simultaneously. Use of sol electrophoresis and soft lithography can directly pattern PZT films without etching. The third topic is design considerations encountered in the development of PZT thin-film microactuators. For example, one needs to confirm that the corner frequency of the PZT RC-circuit is much higher than the lowest natural frequency of the actuator's mechanical structure, so that the bandwidth and quality factor will not be sacrificed. Also, accuracy of finite element analyses cannot be readily assumed, because uncertainties in piezoelectric constants and boundary conditions can significantly alter the predictions from the finite element analyses. [ABSTRACT FROM AUTHOR]