MRS Bulletin

Technical Feature

Technical Feature

Piezoelectric Thin Films for Sensors, Actuators, and Energy Harvesting

P. Muralt, R. G. Polcawich and S. Trolier-McKinstry

Abstract

Piezoelectric microelectromechanical systems (MEMS) offer the opportunity for high-sensitivity sensors and large displacement, low-voltage actuators. In particular, recent advances in the deposition of perovskite thin films point to a generation of MEMS devices capable of large displacements at complementary metal oxide semiconductor-compatible voltage levels. Moreover, if the devices are mounted in mechanically noisy environments, they also can be used for energy harvesting. Key to all of these applications is the ability to obtain high piezoelectric coefficients and retain these coefficients throughout the microfabrication process. This article will review the impact of composition, orientation, and microstructure on the piezoelectric properties of perovskite thin films such as PbZr1−xTixO3 (PZT). Superior piezoelectric coefficients (e31, f of −18 C/m2) are achieved in {001}-oriented PbZr0.52Ti0.48O3 films with improved compositional homogeneity on Si substrates. The advent of such high piezoelectric responses in films opens up a wide variety of possible applications. A few examples of these, including low-voltage radio frequency MEMS switches and resonators, actuators for millimeter-scale robotics, droplet ejectors, energy scavengers for unattended sensors, and medical imaging transducers, will be discussed.

Paul Muralt can be reached at the Swiss Federal Institute of Technology, Switzerland; tel. 41–21–69–34957; and e-mail paul.muralt@ epfl.ch.

Muralt is an adjunct professor at the Swiss Federal Institute of Technology EPFL in Lausanne, Switzerland. He received a diploma in experimental physics and a PhD degree in solid-state physics from the Swiss Federal Institute of Technology ETH in Zurich. At EPFL, he started activities in ferroelectric and piezoelectric thin films and microelectromechanical system (MEMS) devices. Currently, he leads a group in thin film, MEMS, and nanotechnology activities at the Ceramics Laboratory of the Materials Science Institute. His interests are in thin film growth and integration issues of mostly functional oxide materials, property-microstructure relationships, and applications in semiconductor and microelectromechanical devices. Examples of the latter include ultrasonic micromotors, pyroelectric detector arrays, piezoelectric microphones, micromachined ultrasonic transducers, and radio frequency filters based on bulk acoustic waves in thin films. More recent research includes the fabrication and study of ferroelectric nanostructures and oxygen ion conductors for micro solid oxide fuel cell investigations. Muralt delivers lectures in thin film deposition, micro- and nanotechnology, and basic ceramics. He also served as a 2008 MRS Spring Meeting Chair.

Ronald G. Polcawich can be reached at the U.S. Army Research Laboratory, Adelphi, MD 20783, USA; tel. 301–394–1275; fax 301–394–1559; and e-mail ronald.g.polcawich@us.army.mil.

Polcawich is a staff researcher in the Microand Nanomaterials and Devices Branch of the United States Army Research Laboratory (ARL) in Adelphi, MD. He received his BS degree in materials science and engineering from Carnegie Mellon University (1997), his MS degree in materials from Penn State University (1999), and his PhD degree in materials science and engineering from the Pennsylvania State University (2007). He is currently the team lead for the radio frequency microelectro-mechanical system (RF MEMS) and mm-scale robotics programs at ARL. His research activities include materials processing of PZT thin films, MEMS fabrication, piezoelectric MEMS, RF components, MEMS actuators, and mm-scale robotics. In addition, Polcawich is a member of the Institute of Electrical and Electronics Engineers (IEEE) and the Materials Research Society.

Susan Trolier-McKinstry can be reached at the Pennsylvania State University, PA 16802, USA; tel. 814–863–8348; fax 814–865–2326; and e-mail STMcKinstry@psu.edu.

Trolier-McKinstry is a professor of ceramic science and engineering and director of the W.M. Keck Smart Materials Integration Laboratory at the Pennsylvania State University. Her main research interests include dielectric and piezoelectric thin films, the development of texture in bulk ceramic piezoelectrics, and spectroscopic ellip-sometry. Trolier-McKinstry has been actively involved with the Materials Research Society (MRS), having served as a MRS Fall 2003 meeting co-chair, a symposium organizer, and as a member of the Program Development Subcommittee.

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