Pre-stressed piezoelectric bimorph micro-actuators based on machined40 µm PZT thick films: batch scale fabrication and integration with MEMS

Abstract

The projected force–displacement capability of piezoelectric ceramic films in the 20–50 µm thickness range suggests that they are well suited to many micro-fluidic and micro-pneumaticapplications. Furthermore when they are configured as bending actuators and operated at ∼ 1 V µm − 1 they do not necessarily conform to the high-voltage, very low-displacement piezoelectricstereotype. Even so they are rarely found today in commercial micro-electromechanicaldevices, such as micro-pumps and micro-valves, and the main barriers to making themmuch more widely available would appear to be processing incompatibilities rather thancommercial desirability. In particular, the issues associated with integration of these devicesinto MEMS at the production level are highly significant and they have perhaps receivedless attention in the mainstream than they deserve. This paper describes a fabricationroute based on ultra-precision ceramic machining and full-wafer bonding for cost-effectivebatch scale production of thick film PZT bimorph micro-actuators and their integrationwith MEMS. The resulting actuators are pre-stressed (ceramic in compression) which givesthem added performance, they are true bimorphs with bi-directional capability and theyexhibit full bulk piezoelectric ceramic properties. The devices are designed tointegrate with ancillary systems components using transfer-bonding techniques.The work forms part of the European Framework 6 Project ‘Q2M—Quality toMicro’.