Lead Free KNN Thin Films Based Actuator Devices Realized in a 200 MM Silicon Technology for Piezoelectric Transducer Applications

This paper reports the realization and characterization of (K,Na)NbO3 (KNN) based actuator devices in a 200 mm MEMS line for piezoelectric transducer applications. State-of-the-art KNN films of thickness 1.9 µm were sputter deposited on 200 mm SOI substrates and integrated into various types of actuator devices using industrial compatible MEMS process. These actuators show excellent performance, close to Pb(Zr,Ti)O3 (PZT) based counterparts. This first demonstration opens the way to the replacement of PZT, which must be banned due to lead, in piezoMEMS industry in the near future.

INTRODUCTION

PZT is today the most used and the best performing piezoelectric material for micro-actuator applications (inkjet printheads, micro-speakers, scanner, haptics…) [1]. However, its use is threaten since 2006 by the Restriction of Hazardous Substances (RoHS) directive [2], as some elements such as lead are, with some temporary exceptions, prohibited. After more than 15 years searching for a lead free alternative, KNN is seen today as one of the most promising candidates for replacing PZT as it exhibits piezoelectric properties close to the latter. However, to enter in the piezoMEMS industry, some standards have to be fulfilled, like the deposition and the integration on 200 mm Si wafer following an industrial process. Very recently, it has been reported that KNN films could be deposited on such large substrate with good thickness uniformity across the wafer using a mass-production ready sputtering tool [3]. In the present paper, we report the integration and the characterization of such KNN films into MEMS actuator devices.