Effects of poling, and implications for metastable phase behavior in barium strontium titanate thin film capacitors

Barium strontium titanate (Ba0.5Sr0.5TiO3–BST) thin film capacitor structures were made using pulsed laser deposition, and their functional properties were monitored with varying temperature. It was found that poling at low temperature could induce distinct differences in the behavior of the dielectric constant and loss tangent, on heating. In relatively thick BST films (>∼650nm), poling the sample at 80K produced a change from a single broad anomaly to one in which three distinct anomalies could be observed. The temperatures of these anomalies (∼140, ∼200, and ∼260K) were close to those known to be associated with phase transitions in bulk. Monitoring changes in polarization loops with temperature confirmed the likelihood that the dielectric anomalies observed were indeed the result of phase transitions in the films. Unusually, though, when the films were poled at 150K, and then cooled to 80K prior to collection of dielectric data on heating, the dielectric anomaly around 140K was completely suppressed. ...