Design of MEMS PZT circular diaphragm actuators to generate large deflections

This paper presents a design of lead zirconate titanate (PZT) circular diaphragm actuators to generate large deflections. The actuators utilize a unimorph structure consisting of an active PZT and a passive thermally grown SiO₂ layer. The diaphragm structures were formed by deep reactive ion etching (DRIE). Two different designs, where the PZT layer in the diaphragm actuators was driven by either interdigitated (IDT) electrodes or parallel plate electrodes, were investigated. Both finite element analysis and experimental results proved that the IDT configuration is favorable to generate deflections larger than the diaphragm thickness. The IDT configuration creates an expansion in the PZT layer in the radial direction and a contraction in the tangential direction under forward bias, which enables large deflections. At applied voltages of 100 V, an actuator 800μm in diameter could generate center deflections of around ∼ 7.0μm, significantly greater than the diaphragm thickness of 2.8μm. The deflection profiles for the diaphragm actuators became flatter when an inactive region in the annular IDT configuration was introduced. There was also a proportional reduction of the maximum deflection.