Hysteresis Offset in Stress Induced Polarization-Graded Ferroelectrics
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U12.20.1
Hysteresis Offset in Stress Induced Polarization-Graded Ferroelectrics J. V. Mantese, N. W. Schubring, A. L. Micheli, and M. P. Thompson Delphi Research Laboratories, Shelby Township, MI R. Naik Department of Physics & Astronomy, Wayne State University, Detroit, MI G. W. Auner Department of Electrical & Computer Engineering, Wayne State University, Detroit, MI I. B. Misirlioglu, Z.-G. Ban, and S. P. Alpay Department of Metallurgy & Materials Engineering and Institute of Materials Science, University of Connecticut, Storrs, CT
ABSTRACT Polarization-graded ferroelectrics and their electrically active counterparts, graded ferroelectric devices (GFDs) and transpacitors has been achieved in a number ways, including a variation in the composition of the material, or impressing a temperature gradients across the structure.In this article, we report how these same devices can be formed from homogeneous ferroelectric films of lead strontium titanate by imposing stress gradients on the materials normal to their electrode surfaces. A qualitative description of asymmetric hysteresis behavior based on a modified Landau potential is provided. INTRODUCTION Polarization-graded ferroelectrics and their associated active structures, gradedferroelectric devices (GFDs) and transpacitors, have been characterized as the dielectric analogues of semiconductor diode junctions and transistors [1,2]. Such devices are usually formed from planar, capacitive-like structures by establishing a gradient in electric polarization normal to the electrode surfaces. Most recently, the gain characteristics of transpacitor charge amplifiers have been measured. In this latter configuration, it was found that the gain factors are remarkably similar to transistor current amplifiers [2]. It is well known that the ferroelectric spontaneous polarization, Ps is a function of: material composition, c; temperature, T; and stress, σ; i.e. Ps=Ps(c, T, σ) [3,4]. Consequently, it has been possible to form GFDs from a variety of material systems, both by grading the composition of the ferroelectric and by imposing temperature gradients normal to the electrode surfaces [5-12]. The latter, temperature-based, experiments convincingly demonstrate that extraneous artifacts, such as asymmetric electrical contacts and space charge regions near the electrode surfaces, are not the origin of the observed aberrant (“up” and “down”) hysteretic characteristics of these devices [5]. In this paper, we show that homogenous ferroelectric structures in the presence of a gradient in stress can gives rise to polarization-graded structures, which in turn yield the unconventional hysteresis seen in GFDs and transpacitors. We also show that this unusual phenomenon of hysteresis offset can be explained by using a Landau phenomenological model.
U12.20.2
EXPERIMENT Approximately 4 µm thick lead strontium titanate (PST) films, were deposited on 0.02 cm thick platinum foil substrates by metalorganic decomposition. Metal oxide precursors consisting of: titanium (IV) 2-ethylhexoxide,
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