In situ Growth of Fatigue-free SrBi2Ta2O9 Films by Pulsed Laser Ablation

Abstract

In situ growth of SrBi₂Ta₂O₉ (SBT) films as a function of Bi concentration in the target, substrate temperature, oxygen pressure, and the thickness of bottom Pt electrode by pulsed laser deposition was studied. The SBT phase initially formed at a temperature of 500–520 °C. The SBT films grown from the stoichiometric target generally showed Bi deficiency. A well-crystallized and stoichiometric SBT film could be grown at a temperature of 550–580 °C in 300 mTorr of O₂ from the surplus Bi targets, which showed c-axis preferred orientation. The formation temperature of SrTa₄O₁₁ (ST) phase was above 600 °C, depending on the Bi concentration in the target. Higher oxygen pressure raised the formation temperatures of the SBT and ST phases and concomitantly enriched the Bi concentration of the SBT films. For the bottom Pt electrode 1200 Å thick, the voids were not observed in the SBT overlayer until the deposition temperatures were above 590 °C. Annealing at temperatures above 700 °C in an atmosphere of O₂ was required to improve the contact between Pt electrode and the SBT film and hence the ferroelectric properties of the SBT film. In the present study, a smooth, stoichiometric, and c-axis oriented SBT film, about 350 nm thick, could be grown on Pt (1200 Å)/Ti/SiO₂/Si at a temperature of 550–580 °C in 300 mTorr of O₂ from the Bi surplus targets, which showed remnant polarization (Pr) of 3.0–3.5 μC/cm² and coercive field (Ec) of 30–40 kV/cm at 4 V. No fatigue was observed up to 10⁹. switching cycles