A Feasibility Study of PZT Thin-Film Microactuators for Hybrid Cochlear Implants

Hybrid cochlear implants would integrate electric and acoustic auditory stimulation into a single unit to rehabilitate patients with sensori-neural hearing loss. Conceptually, hybrid cochlear implants consist of an electrode array, as in traditional cochlear implants, and an acoustic microactuator to generate pressure waves inside the cochlea. To enable hybrid cochlear implants, one must develop acoustic actuators small enough to be placed directly into the cochlea. In this study, the microactuators consist of a silicon diaphragm and a lead-zirconate-titanate oxide (PZT) thin film. Two actuators are tested. For the first actuator, the diaphragm size is 1.1 mm by 1.1 mm, the diaphragm thickness is about 12 mum, and the PZT film thickness is 1 mum. The microactuator is tested in an unloaded condition (in air) and a loaded condition (with water and glass sheets) equivalent to a loading of 17 Pa. The microactuator presents a constant displacement of 16 nm, when the driving voltage is sinusoidal with amplitude of 5 V and frequency ranging from 500 Hz to 10 kHz. For the second actuator, the diaphragm size is 800 mum by 800 mum, the diaphragm thickness is 1 mum, and the PZT film thickness remains 1 mum. The second actuator presents a displacement of 6 nm, when the sinusoidal driving voltage is 7.5 V in amplitude. Given that the motion of the stapes in normal hearing is 10-30 nm when the incoming sound pressure is 1 Pa (i.e., 94 dBA), the PZT thin-film microactuators are a feasible design for hybrid cochlear implants