Design of MEMS PZT Circular Diaphragm Actuators to Generate Large Deflections

Abstract

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 SiO 2 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 800 m in diameter could generate center deflections of around 7.0 m, significantly greater than the diaphragm thickness of 2.8 m. 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. [1671]Index Terms-Diaphragm, lead zirconate titanate (PZT), microactuator, microelectromechanical systems (MEMS), piezoelectric unimorph.

What happens turning a 250-μm-thin piezo-stack sideways?

“…They compared the IDT-induced mechanical deflections with common deflection of thin film d 31 diaphragm actuators. Both show downward deflection, which is in the direction of the passive membrane, under forward bias (Hong et al 2006).…”

Polar Oxide Thin Films for MEMS Applications

“…In actuators, a larger deflection effect was measured in this configuration [32]. In addition, the compressive piezoelectric stress may yield larger deflections of membranes (which was indeed observed [78]), and does not provoke cracking of PZT, as may occur in very thick, dense PZT thin films. In energy scavenging, the use of interdigitated electrodes in conjunction with ferroelectrics is practically necessary since the harvested voltage must be as large as possible [79,80].…”

Effects of residual stresses on lead–zirconate–titanate (PZT) thin-film membrane microactuators

“…This often occurs when the membrane is released from a bulk structure during the fabrication [24][25][26]. Therefore, experimentally measured surface warping can serve as an indirect evidence of significant residual stresses.…”