Effects of Mo- and W-doping and annealing processing on the ferroelectric properties of sputtered (Bi, Pr)4Ti3O12 films

The microstructures and ferroelectricity of Mo6+- and W6+-doped (Bi,Pr)4Ti3O12 films, i.e., (Bi,Pr)4Ti3−xMoxO12 (BPTMx) and (Bi,Pr)4Ti3−xWxO12 (BPTWx), as functions of the dopant concentration and annealing processing were studied. For BPTMx and BPTWx films the remanent polarization (2Pr) was improved with x=0.01, while it was degraded with x larger than 0.01. The doping of Mo6+ or W6+ into BPT films can simultaneously induce three effects on the 2Pr, i.e., reducing the amount of oxygen vacancies, enhancing c-axis-oriented growth, and decreasing the grain size. The first effect improves the 2Pr, while the others suppress it. The 2Pr and dielectric properties of the films subjected to two-step annealing, i.e., annealed at 625 °C before deposition of upper Pt electrodes and then annealed at 750 °C after deposition, were significantly improved. This result can be explained in terms of less interfacial reactions between the upper Pt electrodes and the ferroelectric films for two-step annealing.