Effect of Capacitor Configuration on Oxygen-dependent Electrical Properties of Ferroelectric Pb(Zr, Ti)O 3 Thin Films
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Effect of Capacitor Configuration on Oxygen-dependent Electrical Properties of Ferroelectric Pb(Zr,Ti)O3 Thin Films M. A. McCormick, E. B. Slamovich, and P. Metcalf Purdue University, W. Lafayette, IN 47907 M. McElfresh Lawrence Livermore National Laboratory, 7000 East Ave., Livermore, CA 94550 ABSTRACT Polarization versus applied field (P-E) hysteresis loop measurements on Pb(Zr,Ti)O3 (PZT) thin films were performed using a controlled-atmosphere probe station. Measurements were made using two different capacitor configurations, each producing differing results. The capacitor configurations included using either the typical arrangement of two top electrodes (planar) or an arrangement using contacts to the top and the bottom electrodes (sandwich). The films included PZT films deposited using pulsed laser deposition (PLD) and commercially-available rfsputtered PZT thin films. Qualitatively similar results were obtained for both types of films. For both PLD and Ramtron PZT films, translation of ferroelectric hysteresis loops along the polarization axis was observed for sandwich capacitors. The magnitude of this voltage was strongly dependent on the partial pressure of oxygen at room temperature. Translations were not observed for the same films using the planar capacitor configuration. However, for both sandwich and planar configurations, the thin film capacitance was sensitive to changes in pO2. INTRODUCTION Recently, Brazier et al. reported anomalous ferroelectric properties for Pb(Zr,Ti)O3 (PZT) thin films [1]. In particular, polarization versus applied electric field hysteresis loops, measured using a Sawyer-Tower circuit, were observed to translate vertically along what is normally regarded as the polarization axis. It was shown that the hysteresis loop translations are consistent with a dc voltage offset that develops across the sample capacitor when it is driven with an ac electric field. Furthermore, the direction and magnitude of the translation were shown to depend on the oxygen partial pressure (pO2) above the film during measurement. One distinctive difference between the method used by Brazier et al. and that used by many other groups is the capacitor configuration utilized. The typical ferroelectric measurement on a thin film involves using a pair of contacts on the top of the film, essentially creating a pair of capacitors in series sharing a common bottom electrode. Here this is referred to as the planar capacitor configuration. On the other hand, Brazier et al. made contacts to the top and bottom electrodes, which will be referred to as the sandwich capacitor configuration. In this work, the planar and sandwich capacitor configurations are shown to produce different results. To help confirm the observations of voltage offsets as a material property, rather than a depositiondependent property, PZT films obtained from Ramtron Corporation were tested. The results for both PLD and Ramtron PZT thin films were qualitatively similar and will be discussed in detail. EXPERIMENTAL Thin films of highly oriented (
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