Feasibility study of a partially released lead-zirconate-titanate (PZT) Diaphragm micro-actuator

Piezoelectric thin-film micro-sensors and actuators often appear in the form of a diaphragm anchored around its entire boundary. When a micro-device is scaled down in size, its sensitivity reduces and natural frequency increases, drastically lowering its performance. The purpose of the paper is to study the feasibility of introducing through-etched slots to partially release the diaphragm at its anchor. As a result, a micro-device can be scaled down in size without significantly altering its sensitivity and natural frequency. In this paper, we first present a finite element simulation proving the concept. We then describe processing steps to fabricate a lead-zirconate-titanate (PZT) thin-film diaphragm sensor/actuator with a partially released boundary. Challenges encountered in the fabrications, such as cat ear and electrode non-uniformity, are explained and overcome. As a case study, we demonstrate the feasibility to design, fabricate, and test an intra-cochlear micro-actuator probe that employs three partially released PZT diaphragms at the tip of a cantilever. Experimental measurements indicate that the sensitivity is dominated by the diaphragm deflection, while the first natural frequency is dominated by the cantilever structure. Finite element simulations not only confirm the experimental measurements but also optimize diaphragm dimensions for sensor/actuator performance.