Effects of oxygen partial pressure and ion doping on the ferroelectricity and microstructures of sputter-deposited Bi3.25La0.75Ti3O12 films

The effects of oxygen partial pressure during deposition and V and P doping on the microstructures and ferroelectricity of sputter-deposited Bi3.25La0.75Ti3O12 (BLT) films on Pt/SiO2/Si(100) were studied. At the deposition pressure of 4 mTorr the O2/(Ar+O2) ratio in the range of 0.4-0.5 allowed the films to achieve a larger remnant polarization (2Pr). For the (Bi3.25La0.75)(Ti3−xVx)O12 films, the 2Pr first increases with increasing the V concentration (x) up to 0.03, then gradually decreases in the range of x=0.05-0.1 and drastically decreases at x=0.15. The doping of V into the BLT films can simultaneously induce two contrary effects on the 2Pr, i.e., reducing the amount of oxygen vacancies and decreasing the grain size, which result in the improvement and degradation of 2Pr, respectively. The two effects are similar to those induced by the factor of oxygen partial pressure during deposition. The degradation of 2Pr for the P-doped BLT films can be ascribed to the dissociation of BiO bonds and reduction of grain size due to P doping.