Thin Film Bi-based Perovskites for High Energy Density Capacitor Applications

Colin Shear is a senior in Physics and in the University Honors College. His thesis work was supervised by Prof. Brady Gibbons of Materials Science/Mechanical Engineering.

Pulsed laser deposition (PLD) was used to create 0.1-Bi(Zn¬0.5Ti0.5)O3 – 0.9-BaTiO3¬ (BZT-BT) thin films to examine the effects of laser energy (2.25 or 2.5 J/cm2), pulse frequency (2 Hz or 5 Hz), and deposition temperature (550, 600, 650, and 700 °C) on the electrical properties of the films. These effects were analyzed by characterizing the films using X-ray diffraction (XRD), spectroscopic ellipsometry (SE), and electrical measurements including dielectric constant, dielectric loss, and polarization hysteresis (P-E) response. The deposition temperature and pulse frequency combined to create good perovskite phase development (as seen in the XRD data) and large grains in high temperature/low frequency films, while producing poor perovskite phase development and fine grains in low temperature/high frequency films. Good phase development resulted in high dielectric constants while reducing the breakdown strength, suggesting that grain boundaries and poor phase development block electron conduction. Energy storage densities were on the order of 1 J/cm3 and did not vary significantly across deposition parameters, as higher dielectric constants were paired with lower breakdown strengths.