Effects of W doping and annealing parameters on the ferroelectricity and fatigue properties of sputtered Bi3.25La0.75Ti3O12 films

Abstract

The ferroelectricity and fatigue properties of Bi3.25La0.75Ti3O12 (BLT) and W-doped BLT (BLTWx) films, x=0.01, 0.03, 0.05, and 0.1, annealed in air as a function of annealing temperature and time were studied. Most of the polarization–electric-field (P–E) loops of BLT and BLTWx films measured immediately after annealing showed leaky behavior. Upon aging at room temperature for 1–4 h, the P–E loops became saturated. The excess oxygen vacancies remained in the films after annealing and subsequent quenching may be responsible for the leaky behavior. Annealing in O2 at 700 °C and below enhanced the formation of pyrochlore Bi2Ti2O7 and thus degraded the ferroelectricity of the films. The remnant polarization (2Pr) of the samples annealed at a temperature of 675–700 °C for 10–60 min increased with the annealing time, while that of the samples annealed at 750 °C were reduced due to the loss of Bi. The 2Pr of BLTWx films increased with the W concentration up to x=0.03 and then decreased, revealing that W doping induces two contrary effects on Pr, i.e., reducing the amount of oxygen vacancies and causing less structure distortion. In addition, W doping significantly improved the fatigue properties of BLTWx films. The leakage current of BLTWx films was in the order of 10−7 A/cm2 at the field of 200 kV/cm, being at least an order of magnitude lower than that of BLT films.