Textured Ferroelectric Thin Films: Synthesis, Characterization, and Influence of Compositional Grading on the Dielectric Behavior

Abstract

This dissertation focuses on two topics concerning the connections between structure and property in ferroelectric thin films. First, the synthesis of highly oriented ferroelectric thin films is addressed, where the texture is needed to generate high strains that rely on electromechanical domain switching. The ferroelectric films are integrated with oxide electrodes onto single crystal MgO and Si substrates using biaxially-textured MgO as buffer layers. The second topic focuses on modeling the dielectric behavior of compositionally graded ferroelectrics. The functional ferroelectric (Pb,Ba)TiO3 films are deposited by metalorganic chemical vapor deposition (MOCVD). SrRuO3, grown by pulsed laser deposition (PLD), is a lattice-matching electrode. Both the ferroelectric and oxide electrode layers are found to inherit the biaxial texture of the underlying MgO template, which can be deposited by ion beam assisted deposition (IBAD) directly on Si-based substrates. In addition, we demonstrated control of the ferroelectric film stoichiometry using a spectroscopic control loop that monitors the ultraviolet spectra of the gas-phase MOCVD precursors during growth. Detailed studies of the microstructural details of these films will be presented. The second topic of this thesis explores the dielectric behavior of functionally graded ferroelectric thin films. Homogenous ferroelectrics offer the possibility of engineering a tunable dielectric response for components in microwave circuits. However, this approach often leads to an undesired temperature sensitivity. Compositionally-graded (Ba,Sr)TiO3 ferroelectric films have been explored as a means of redressing this sensitivity, but experimental observations vary depending on geometry and other details. A continuum model is presented to calculate the capacitive response of graded ferroelectric films with realistic electrode geometries by accurately accounting for the polarization distribution and long-range electrostatic interactions. We show preferred designs that are extremely effective in obtaining high and temperature-stable dielectric properties.