Domain wall contributions to the properties of piezoelectric thin films Nazanin Bassiri-Gharb & Ichiro Fujii & Eunki Hong & Susan Trolier-McKinstry & David V. Taylor & Dragan Damjanovic Received: 27 September 2006 / Accepted: 15 January 2007 / Published online: 8 March 2007 # Springer Science + Business Media, LLC 2007 Abstract In bulk ferroelectric ceramics, extrinsic contribu- tions associated with motion of domain walls and phase boundaries are a significant component of the measured dielectric and piezoelectric response. In thin films, the small grain sizes, substantial residual stresses, and the high concentration of point and line defects change the relative mobility of these boundaries. One of the consequences of this is that thin films typically act as hard piezoelectrics. This paper reviews the literature in this field, emphasizing the difference between the nonlinearities observed in the dielectric and piezoelectric properties of films. The effect of ac field excitation levels, dc bias fields, temperature, and applied mechanical stress are discussed. Keywords Review . Domain walls . Piezoelectric thin films 1 Introduction With their superior dielectric and piezoelectric response, perovskite-structured ferroelectric thin films have attracted attention for application in capacitors and microelectro- mechanical systems (MEMS). The large dielectric response of these materials is due in part to intrinsic (averaged crystallographic response of the ferroelectric material’ s domains) and in part due to extrinsic contributions, mainly due to the motion of the domain walls and phase boundaries. In perovskite ferroelectrics, domain walls can be moved by electric fields, stresses, or combinations of the two. Indeed, domain wall motion is the process by which the spontaneous polarization is oriented during poling processes to yield a net piezoelectric effect. Domain wall motion is an important contributor to the dielectric response of polycrystalline ceramic materials, and is a major component of the extrinsic piezoelectric response [1]. Extrinsic contributions can be responsible for up to ∼75% of the dielectric and piezoelectric response of a ferroelectric ceramic [2]. However, while domain wall motion is extremely useful in increasing the achievable response, the walls move through a potential field that can locally pin the walls, for example due to local elastic or electric fields. Motion is thus a progressive process of freeing, moving, and re-pinning the walls. As a result, domain wall motion is hysteretic and nonlinear. Due to extrinsic contributions, the effective dielectric and piezoelectric coefficients of ferroelectrics depend on the applied electric field strength and frequency [2]. As many applications require thinner films (sensors and actuators in MEMS, multilayer capacitors, etc.) an understanding of the J Electroceram (2007) 19:47–65 DOI 10.1007/s10832-007-9001-1 N. Bassiri-Gharb : I. Fujii : E. Hong : S. Trolier-McKinstry Materials Research Institute, The Pennsylvania State University, University Park, PA 16802, USA N. Bassiri-Gharb : I. Fujii : E. Hong : S. Trolier-McKinstry Materials Science and Engineering Department, The Pennsylvania State University, University Park, PA 16802, USA D. V. Taylor : D. Damjanovic Ceramics Laboratory, Swiss Federal Institute of Technology (EPFL), Lausanne, Switzerland N. Bassiri-Gharb (*) Materials and Device R&D, QUALCOMM MEMS Technologies, Incorporated, 2581 Junction Ave., 120.I., San Jose, CA 95134, USA e-mail: nazaninb@qualcomm.com Present address: D. V. Taylor Nanosys Inc., Palo Alto, CA 94304, USA