Preparation of fatigue-free SrBi₂Ta₂O₉ thin films by r.f. magnetron sputtering and their ferroelectric properties

Fatigue-free bismuth-layered SrBi₂Ta₂O₉ (SBT) films were deposited on Pt/Ti/SiO₂/Si substrates by r.f. magnetron sputtering at room temperature. The variation of structure and electrical properties were studied as a function of annealing temperatures from 750-850°C. The films annealed at 800°C had a composition ratio of Sr: Br: Ta = 0.7:2.0:2.0. X-ray photoelectron spectroscopy signals of bismuth show an oxygen-deficient state within the SBT films. The films annealed at 800°C have a thickness of 200 nm and a relatively dense microstructure. The remanent polarization (2P_r), and the coercive field (2E_c), obtained for the SBT films, were 9.1 μC cm^-2 and 85 kV cm^-1 at an applied voltage of 3V, respectively. The films showed fatigue-free characteristics up to 10¹⁰ cycles under 5V bipolar square pulses. The leakage current density was about 7 x 10^-7 A cm^-2 at 150kV cm^-1. The SBT films prepared by r.f. magnetron sputtering were attractive for application to non-volatile memories.