Piezoresponse Measurement and Imaging of Electromechanical PZT and PZN-BT thin Films
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Piezoresponse measurement and imaging of electromechanical PZT and PZN-BT thin films C. Morros, M.H.Corbett, G. Catalan, J.M. Gregg and R.M. Bowman Condensed Matter Physics & Materials Science Research Division, School of Mathematics & Physics, Queen’s University of Belfast Belfast BT7 1NN UK ABSTRACT Pulsed laser deposition (PLD) was used to growth thin films of lead zirconium titanate (PZT) and lead zinc niobate-barium titanate (PZN-BT). The PZT films were prepared from commercial PZT-5H ceramic target and the PZN-BT made from target made using a modified Columbite method. The PZT films had dielectric constants of 300 and loss of 0.03 at 10kHz, whilst for the PZN-BT films they were 350 and 0.03 respectively at 300K. Hysteresis measurements confirmed their switching properties A piezoresponse microscope based on a modified atomic force microscope was developed to determine electromechanical response at a sub-micrometer resolution. The PZT films yielded d33 ~100pm/V. Mapping measurements on the PZT demonstrated local switching of individual grains. First measurements of piezoresponse of PZN-BT yielded values in the region 150-200 pm/V.
INTRODUCTION Recently there has been great interest in thin film applications of electroceramics, for example for high frequency ultrasound imaging of tissue [1]. This has resulted in effort to prepare and characterise electroceramic materials and their responses at the micron and submicron level. Conventional methods such as laser Doppler interferometry are of little use, particularly with the potential for small sample geometry’s in thin films. Recently, piezoresponse imaging (a generic term to describe scanning probe microscope based electromechanical measurement) has been developing particularly with lead zirconium titanate (PZT) films [2,3]. Much of the work is stimulated by applications of PZT for memory and electronics application. In this paper we describe the development of our piezoresponse microscope and demonstrate its functionality by measurement of the properties of routine PZT thin films. Due to the difficulty of synthesis, a small number of groups have access to high quality elecrostrictive thin films such as lead magnesium niobate (PMN) and lead zirconium niobate (PZN) of interest in next generation transducer and actuator applications. Therefore, few if any, investigations by piezoresponse on these systems have been reported. In this paper we report for the first time the electromechanical response of Pb(Zn1/3Nb2/3)O3-BaTiO3 (PZN-BT) films using piezoresponse techniques.
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EXPERIMENT
PZT thin film growth The thin films were prepared by standard pulsed laser deposition. A SrRuO3 conducting lower electrode is grown on the substrate prior to the growth of the electroceramic thin film. This takes place at 800 oC and the SrRuO3 is typically 150 nm thick. For PZT growth we used a 1” diameter polycrystalline ceramic disc cut from a rod of commercial PZT-5H (Morgan-Matroc). The films were prepared using conditions similar to our protocols for other lead based com
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