Nanostructural tuning of the texture of PZT pervoskite thin films grown by RF sputtering for piezoelectric MEMS
- PDF / 2,372,102 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 31 Downloads / 320 Views
Nanostructural tuning of the texture of PZT pervoskite thin films grown by RF sputtering for piezoelectric MEMS Andrea Mazzalai1, Martin Kratzer2, Ramin Matloub1, Cosmin Sandu1, and Paul Muralt1 1 Ceramics Laboratory, École Polytechnique Fédérale de Lasuanne – EPFL Lausanne, CH-1015, Switzerland. 2 Oerlikon Systems R&D, Oerlikon Advanced Technologies AG Balzers, LI-9496, Liechtenstein. ABSTRACT Currently, large efforts are going on to scale up PZT thin film processes for large volume MEMS fabrication. It is critical to complete the scaling up with optimized film properties. In this work we report about microstructural control and piezoelectric properties of RF magnetron sputtered PZT (Pb(Zrx,Ti1-x)O3) thin films. The former is a prerequisite to achieve good properties homogeneously on the entire wafer, and with a good repeatability. We focus on the use of a commercial tool capable to reach a deposition rate of 1nm/sec with a thickness uniformity better than +/-3%. We show particularly how the texture can be chosen between (100) and (111) orientation upon tuning the thickness of a very thin TiO2 seed layer on fully passivated Pt electrodes. The surface morphology as resulting from the various grain shapes is strongly influenced by the self-bias established on the substrate, and by the growth temperature. PZT films with compact grain structure and flat surface reached a transverse piezoelectric coefficient e31,f of -23±1 C/m2 in the actuator mode (converse piezoelectric effect) and a dielectric strength of 0.5MV/cm. Both are remarkable values for un-doped, pure PZT thin films. INTRODUCTION The perovskite compound lead-zirconate-titanate Pb(ZrxTi1-x)O3 (PZT) is since many years by far the most popular material among the ferroelectric ceramics for piezoelectric applications, particularly for actuators and ultrasonic transducers. The optimal composition at x=0.53 is right at the morphotropic phase boundary between a tetragonal and a rhombohedral phase where piezoelectric and dielectric properties are peaking [1]. Significant efforts have been spent over the last 20 years for growing PZT thin films on silicon substrates for the realization of MEMS devices. It was recognized that PZT thin films (in contrast to ceramics) grow with a defined texture upon suitably controlling nucleation, allowing for higher piezoelectric coefficients than with random orientations of grains. In case of polycrystalline films grown on Pt(111) electrode films, the ideal texture was found to be {100} [2]. The remarkable piezoelectric coefficients achieved in micrometer-thick films allow for the generation of large forces, and consequently large strokes in suitable flexural structures. The recent progress in this integration work caught large interests of industry needing miniaturized, high-speed, and lowpower actuators. Piezo-MEMS devices need in general less power, less voltage, and are faster than devices based on competing principles. Many interesting devices have been developed or improved, such as faster ink-jet printheads with higher dot den
Data Loading...
