Mara Howell

Materials Science and Engineering

Purdue University
Advising Professor: Eric Kvam
Project Title Dielectric Properties of Ceramic Thin Films

Introduction

Capacitors are used in almost every device in the modern microelectronics industry. They are used to store charge or energy, and can also be used as a control in an RC or RLC circuit. Adding a dielectric material between the electrodes of a capacitor can significantly increase its dielectric constant, which in turn increases the amount of charge or energy that it stores. Barium Titanate in its pure and doped forms is a material that can be used as a dielectric in a capacitor.

Barium Titanate is considered a ferroelectric material. At room temperature it has a tetragonal crystal structure. When a voltage is applied across the material, the titanium ion at the center of the crystal is displaced. The 4+ titanium ion and two corresponding 2- oxygen ions make an electric dipole. The many small dipoles are aligned according to the applied voltage. The large magnitude of these aligned dipoles and the relatively large displacement of the titanium ion lead to a large dielectric constant for the material. The goal of this project is to fabricate Barium Titanate thin films using a Sol Gel process and to test the films for their dielectric properties.

Project Objectives

  • Refine the Sol Gel process used to create Barium Titanate thin films
  • Test the electrical properties of the thin films
  • Explore the effects of dopants on the electrical properties of the films

Eexperimental Approach

  • Plasma sputtering was used to deposit platinum onto the substrate surface, and to create the top electrode for the capacitor
  • Sol Gel processing was used to make a solution of the film
  • Spin coating was used to deposit the film onto the platinum coated substrate
  • X-ray diffraction was used to determine if the phase transformation was completed
  • Atomic Force Microscopy was used to determine grain size in film
  • Optical Microscopy was used to determine porosity and cracking defects
  • Microelectronics testing equipment was used to test electrical properties

Research Findings

  • Using a silicon substrate as opposed to glass drastically reduced porosity, cracking, and warping of the Barium Titanate thin films
  • Annealing at higher temperatures (850o C) led to a more complete phase transition.
  • Breakdown of the film occurs around 40 V; therefore electronic testing should not be done with an applied voltage of over 40 V

Future Work

  • Continue electronics testing on samples
  • Explore the effects of dopants on the electronic properties of the film

 


Fig. 1. XRD of Barium Titanate film sample showing a more complete phase transformation at higher temperatures.
Fig 2. Capacitance vs. Voltage Trend for Barium Titanate Film Sample

Final Presentation

Favorite Webpage

Check out Purdue's Society of Women Engineers