Ferroelectric thin film development

Abstract

The long-term goal of the research project initiated with this thesis is the development of lead-free, fully-transparent ferroelectric devices, such as ferroelectric capacitors or ferroelectric-gate field-effect transistors. Ferroelectric materials exhibit spontaneous polarization with the application of an external electric field, which is persistent upon removal of the applied field, and can be reversed by applying a field of opposite polarity. Ferroelectric thin films can be used in non-volatile memory applications in storage capacitors or as the gate dielectric of a field-effect transistor. Ferroelectric devices are fabricated by the deposition of ferroelectric lead zirconate titanate (PZT) by RF sputtering and by the chemical solution deposition (CSD) method of spin coating. Ferroelectric PZT capacitors are characterized by measuring capacitance and conductance as a function of frequency, and by measuring polarization as a function of applied electric field using a Sawyer-Tower circuit. Ferroelectric PZT capacitors with opaque Au or Ni top electrodes exhibit dielectric constants in the range of »300-600, typical of a ferroelectric film. However, all attempts to fabricate ferroelectric capacitors with transparent top contacts, involving several types of transparent conductors and the use of insulating buffer layers, resulted in charge injection and breakdown before the ferroelectric layer is fully polarized.