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Title:Dielectric and pyroelectric susceptibilities of epitaxial ferroelectric thin films
Author(s):Jambunathan, Karthik
Director of Research:Martin, Lane W.
Doctoral Committee Chair(s):Martin, Lane W.
Doctoral Committee Member(s):Cahill, David G.; King, William P.; Dillon, Shen J.
Department / Program:Materials Science & Engineerng
Discipline:Materials Science & Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Ferroelectric thin films
Lead zirconium titanate (PZT)
Phenomenological models
Thermal energy harvesting
Abstract:The dielectric and pyroelectric properties of ferroelectrics have been utilized extensively in a variety of applications such as memories, transducers, and sensors. Traditionally, such applications have utilized bulk or single crystal versions of ferroelectrics but modern electronic devices increasingly require micro-fabricated architectures on thin-fi lms. Despite spectacular advances in our ability to synthesize high-quality thin fi lms, much remains to be understood regarding the evolution of their dielectric and pyroelectric properties. In the present work, we investigate the dielectric and pyroelectric susceptibilities of ferroelectric thin films with PbZr1-xTixO3 (PZT) as a model system using a combination of phenomenological Ginzburg-Landau-Devonshire (GLD) modeling, epitaxial thin- film growth, and ex situ characterization techniques such as x-ray di ffraction, piezoresponse force microscopy, and electrical measurements. We show that large dielectric and pyroelectric susceptibilities can be obtained in tensile strained PZT thin fi lms due to the displacement of 90° domain walls and thermal expansion mismatch with the substrate. The primary advances made herein that enable this are the development of a polydomain GLD model to predict ferroelectric susceptibilities, the development of a hard-mask technique for the fabrication epitaxial capacitor structures, and the implementation of a phase-sensitive technique for the accurate measurement of pyroelectric properties. We then proceed to study the eff ect of composition and strain gradients on the ferroelectric properties of PZT. A combined theoretical and experimental study indicates that the graded heterostructures possess exotic structural and ferroelectric properties that are largely determined by the structure of the initial growth layer. We show that obtain large residual strains and novel ferroelectric properties (such as large built-in electric elds and low dielectric susceptibility) can be obtained in graded structures that are not found in the single layer variants. Finally, we present preliminary results of pyroelectric energy conversion in a micro-fabricated device utilizing the concepts developed in this work. Analysis of reversible pyroelectric cycles indicate that large temperature ramp rates and power densities can be obtained for thermal to electrical energy conversion in thin films as compared to prior experiments on bulk ferroelectric ceramics.
Issue Date:2013-05-24
Rights Information:Copyright 2013 Karthik Jambunathan
Date Available in IDEALS:2013-05-24
Date Deposited:2013-05

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