Sputtered AlN Thin Films for Piezoelectric MEMS Devices - FBAR Resonators and Accelerometers

Abstract

Over the past two decades, significant advances have been made in the field of micromachined sensors and actuators. As microelectromechanical systems (MEMS) have become mainstream, a clear need for the integration of materials other than silicon and its compounds into micromachined transducers has emerged. MEMS devices based on piezoelectric materials take advantage of the high energy transduction that scales very favorably upon miniaturization leading to an ever-growing interest in piezoelectric films for MEMS applications. Piezoelectric materials provide a direct transduction mechanism to convert signals from mechanical to electrical domains and vice versa. The reversible and linear piezoelectric effect manifests as the production of a charge (voltage) upon application of stress (direct effect) and/or as the production of strain (stress) upon application of an electric field (converse effect). Transducers using piezoelectric materials can be configured either as actuators, when the design of the device is optimized for generating strain or stress using the converse piezoelectric effect, or as sensors when the design of the device is optimized for the generation of an electric signal, using direct piezoelectric effect, in response to mechanical input. Furthermore, piezoelectric devices also allow the integration of sensing and actuating elements in one device (Xu et al., 2002). The elementary piezoelectric effects are given by