Development of a Light-Driven Thin-Film Piezoelectric Microactuator

This paper presents the design, fabrication and experimental characterization of a self-contained light-driven microactuator that could find a potential application in a novel retinal prosthesis. The conceived actuator system comprises of a miniaturized solid-state solar cell connected in series with a thin-film piezoelectric microactuator, both fabricated and integrated on a single chip through conventional microfabrication processes. When irradiated with light, the solar cell generates voltage across the thin-film microactuator, which bends and produces mechanical actuation. The novelty of the actuator system lies in its unique integrated design to meet its unique application requirements of producing the output mechanical actuation for input light energy at low illumination levels in the range of 0.1–3 W/m². The work demonstrates the fabrication feasibility of the miniaturized solar cell and the PZT thin-film microactuator, and characterizes their performance separately. The solar cell is fabricated by creating a p-n junction over a small area on a single crystal p-type silicon substrate. The microactuator is fabricated as a 600 nm sol-gel derived 52/48 PZT thin-film on a silicon diaphragm. The voltage output characteristics of the solar cell, experimentally studied as a function of the incident irradiance, shows an open circuit voltage of 250–300 mV under 0.6–1.6 W/m² irradiance. The PZT thin-film microactuator, actuated under low voltages of 0–700 mV, showed deflections in the range of 0–16 nm. Finally, the light-driven actuation is demonstrated by connecting the miniaturized solar cell with the PZT thin-film microactuator and measuring deflections of 5–7 nm under low illumination levels of 0.6–1.6 W/m².