Piezoelectric Characterization of Bulk and Thin Film Ferroelectric Materials using Fiber Optics - MTI Instruments - #1

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MTI Instruments, Inc. 325 Washington Avenue Extension Albany, NY 12205 PH: +1-518-218-2550 OR USA TOLL FREE: 1-800-342-2203 FX: +1-518-218-2506 sales@mtiinstruments.com www.mtiinstruments.com APPLICATION NOTE Piezoelectric Characterization of Bulk and Thin Film Ferroelectric Materials using Fiber Optics J.T. Dawley*, G. Teowee**, B.J.J. Zelinski*, and D.R. Uhlmann* *Department of Materials Science and Engineering University of Arizona, Tucson, AZ 85721. **Donnelly Corporation 4545 E. Fort Lowell Rd., Tucson, AZ 85712 Abstract In this study, the use of a fi ber optic technique for the measurement of the piezoelectric properties of ferroelectric bulk and thin fi lm samples was investigated. The strain and piezoelectic properties (namely the d33 coeffi cients) were measured using the MTI-2000 Fotonic Sensor, which uses the principle of the optical lever to resolve very small changes in sample displacement (1 Å). Using this technique, we were able to detect the very small strains associated with the converse piezoelectic effect for PVDF fi lms and bulk PZT samples, and correlate the results with data acquired from direct piezoelectric effect measurement. Comparison of the data sets prove that the optical lever would be a useful optical technique for measuring of the d33 values of ceramic thin fi lms, such as BaTiOy ZnO, and PZT. Introduction Voigt’s1 analysis of the free energy of crystals showed that it is possible to measure the d33 of a crystal by two different static methods. The fi rst uses the direct piezoelectic effect and is typically called the normal load method. In this technique, the change in the charge of a sample is measured as a function of the change in applied stress. The stress is applied by placing a load on a metallic tip oriented perpendicular to the fi lm’s surface. With the application of the stress, the sample strains and the equilibrium arrangement of the charged species is disturbed, resulting in the formation of a net charge across the material. This charge appears as a voltage drop across a reference capacitor, in parallel relation to the sample, whose capacitance value must be much larger than the sample in order to fulfi ll the free-fi eld condition.2 The voltage is measured using a multimeter or an electrometer and used to calculate the d33 of the material. Detailed descriptions and discussions of this technique can be found in papers by Lefki and Dormans2 and K. No, et. al3. The other technique used to measure the d33 of materials, especially thin fi lms, is the shrain induced method, which uses the indirect or converse piezoelectric effect. In this method, measurements are made of the strain induced in a sample by the application of an external electric fi eld perpendicular to the surface of the fi lm. Although conceptually simple, measurement of the strain is diffi cult because the strains are on the order of angstroms. During the last 10 years or so, researchers have been studying and using optical techniques, interferometry in particular, to measure the MTII appnote: piezoelectric.pdf - page 1 of 6