Sensors and Actuators A 199 (2013) 98–105 Contents lists available at SciVerse ScienceDirect Sensors and Actuators A: Physical jo u r n al homep age: www.elsevier.com/locate/sna Film-thickness and composition dependence of epitaxial thin-film PZT-based mass-sensors Minh Duc Nguyen a,b,c,∗ , Matthijn Dekkers b,c , Hung Ngoc Vu a , Guus Rijnders b a International Training Institute for Materials Science (ITIMS), Hanoi University of Science and Technology, No. 1 Dai Co Viet Road, Hanoi, Viet Nam b Inorganic Materials Science (IMS), MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500AE Enschede, The Netherlands c SolMateS B.V., Drienerlolaan 5, Building 6, 7522NB Enschede, The Netherlands a r t i c l e i n f o Article history: Received 1 March 2013 Received in revised form 29 April 2013 Accepted 11 May 2013 Available online xxx Keywords: Piezoelectric thin-film cantilever Film thickness Film composition Mass-sensitivity Transverse piezoelectric coefficient a b s t r a c t The transverse piezoelectric coefficient e 31,f and mass-sensitivity were measured on piezoelectric can- tilevers based on epitaxial PZT thin-films with film-thicknesses ranging from 100 to 2000 nm. The highest values of e 31,f and mass-sensitivity were observed at a film thickness of 500–750 nm, while the observed remnant polarization P r and longitudinal piezoelectric coefficient d 33,f values become saturated with a film thickness of 750–1000 nm. To obtain high performance by making use of its optimal film thickness, PZT thin films with various Zr/Ti ratios from 20/80 to 80/20 were studied. The experimental results indi- cated that the ferroelectric property reached a highest remnant polarization P r at a Zr/Ti ratio of 20/80, while the longitudinal piezoelectric coefficient d 33,f increased with increasing Zr content and reaches a maximum at a Zr/Ti ratio of 52/48. The findings suggest that the optimal composition for mass-sensitivity and transverse piezoelectric coefficient e 31,f was shifted to the tetragonal part of the phase diagram with the Zr/Ti ratios of 45/55 and 40/60, respectively. © 2013 Elsevier B.V. All rights reserved. 1. Introduction The ability of piezoelectric materials to convert mechanical energy into electrical energy that can offer potential application in the field of sensors and actuators [1]. Among piezoelectric thin-film materials, Pb(Zr,Ti)O 3 (PZT) is an attractive option for MEMS technology due to their superior ferroelectric and piezoelec- tric properties [2]. However, for ferroelectric device applications, the epitaxial growth of ferroelectric thin films on silicon sub- strates is considered to be a key technology for fabricating thinner and smaller electronic devices, because their leakage currents are expected to be lower than those of polycrystalline films [3–5]. Moreover, epitaxial PZT films also exhibit better ferroelectric and piezoelectric properties than polycrystalline PZT films [6]. One of the most interesting aspects in PZT thin film research is the influence of the film composition on the ferroelectric and piezoelectric properties. The major influence on the film proper- ties results from tetragonal-to-rhombohedral phase transition. In the case of PZT bulk materials, maximum values of polarization, ∗ Corresponding author at: International Training Institute for Materials Science (ITIMS), Hanoi University of Science and Technology, No. 1 Dai Co Viet Road, Hanoi, Viet Nam. Tel.: +84 438680787; fax: +84 438692963. E-mail address: minh.nguyen@itims.edu.vn (M.D. Nguyen). dielectric constant and piezoelectric coefficient have been observed at the morphotropic phase boundary (MPB) composition [7]. The MPB of Pb(Zr,Ti)O 3 is located at a PbZrO 3 :PbTiO 3 ratio of 52:48 and separates the Ti-rich tetragonal phase from the Zr-rich rhombohe- dral phase [8]. The large number of possible polarization directions (14 possible orientations for the MPB, eight [1 1 1] directions for the rhombohedral phase and six [1 0 0] directions for the tetragonal phase) and the consequent extrinsic contribution at this boundary are thought to give rise to the superior ferroelectric and piezoelec- tric properties [8,9]. However, due to the influence of substrate clamping, the properties of thin films show a different trend than that for bulk ceramics [10]. Another interesting aspect of PZT thin film is the dependence of the film thickness on the ferroelectric and piezoelectric properties. The influence of an interfacial layer and residual stress has been proposed as the explanation for the change in the properties with film thickness [11]. Until now, there are many reports that describe the influence of film composition (Zr/Ti) and film thickness on the ferroelectric and piezoelectric properties of PZT films. Results showed that the enhanced remnant polarization and piezoelectric coefficient values are obtained with the increase of film thickness, mainly due to the increased mobility of domains, the reduced film-electrode interfa- cial layer and substrate constraints effects, as well as the decrease of residual tensile stress with increasing film thickness [12–16]. Meanwhile, films with composition close to the MPB showed high dielectric constant and piezoelectric coefficient [17,18] or they 0924-4247/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.sna.2013.05.004