Authors: D. Kaden, S. Gu-Stoppel, H.-J. Quenzer, D. Kaltenbacher, B. Wagner, R. Dudde
Affilation: Fraunhofer Inst. Silicon Technology, Germany
Pages: 176 - 179
Keywords: MEMS, devices, sound transducer, PZT, piezoelectic thin films
Piezoelectric materials are of great interest for powerful actuation in MEMS devices. Due to its large electromechanical coupling coefficient Lead Zirconate Titanate (PZT) is one of the most favourable materials for realisation of fast and energy efficient microactuators. Here we report results of process optimisation for high quality thin film PZT deposition using standard magnetron sputter equipment (Oerlikon Balzers) of up to 2µm thickness at a deposition rate of 45nm/min. A new reliable industrial production process was developed leading to optimised material quality for micromechanical applications. Pt bottom electrode configuration, deposition temperatures and process control have been optimised for thin film piezoelectric coefficients. Optimised PZT films of 1µm thickness show a high dielectric constant εr of 1860 with a maximum remnant polarisation of 48,7µC/cm². A remarkable high transversal piezoelectric module e31,f of -17,3C/m² was achieved with an effective longitudinal d33,f coefficient 160pm/V. Top electrodes were realised in Cr/Au. These electrodes were used as hard masks for structuring of the piezoelectric material. Free standing PZT beams were produced by etch removal of a sacrificial layer. Various designs have been realised. Design examples for new sound transducers in the sound and ultrasound region are presented and discussed.