Development of a lead-zirconate-titanate (PZT) thin-film microactuator probe for intracochlear applications

In this paper, we present design, fabrication, and testing results of a small-scale piezoelectric lead-zirconate-titanate (PZT) thin-film microactuator probe that could be implanted in the inner ear for hearing rehabilitation. The PZT probe would generate a pressure wave directly stimulating perilymph in the cochlea to provide acoustic stimulation. Specifically, the PZT probe is 1-mm wide, 10-mm long, and 0.4-mm thick with a PZT thin-film diaphragm at the tip of the probe serving as an acoustic actuator. The diaphragm size is 0.8 mm x 0.8 mm and the probe is packaged with parylene of 0.25-mu m thickness. The design effort includes finite element simulations to determine thickness of the parylene package as well as back-of-the-envelope calculations of implantation depth of the PZT probe. The fabrication work includes deposition of a PZT thin film via sol gel processes, deep reaction ion etching to form an array of vibrating PZT diaphragms, dicing the wafer to release the PZT probes, and application of parylene layer to package the PZT probes. The testing effort includes measurements of actuator velocity (via a laser Doppler vibrometer) and impedance (via an impedance analyzer) in air and in water. After the PZT probe is submerged in water, its displacement gradually increases and saturates at around 2 h. Impedance measurements also show a similar trend. To explain these phenomena, we hypothesize that water infiltrates into the PZT thin film via diffusion, thus increasing the dielectric constant of the PZT film. SEM images reveal numerous nano-pores on PZT and probe surfaces, indirectly supporting the hypothesis. The PZT probe functions in water for 55 h without breaking down. (C) 2013 Elsevier B.V. All rights reserved.