FREQUENCY-DEPENDENT POLARIZATION IN BiFeO3 THIN FILMS

Single phase BiFeO3 (BFO) thin films were fabricated by chemical solution deposition on Pt/Ti/SiO2/Si(100) structures. J-E (current density vs. electric field) and P-V (polarization vs. voltage) characteristics were measured at room temperature (RT). It is shown in J-E characteristics that sharp increase in the current density occurs at a lower electric field in a thinner BFO film. The P-V hysteresis loops were measured by changing frequencies with triangular voltage pulses from 1 to 100 kHz. The remanent polarization decreases with the frequency mainly between 1 and 20 kHz and the decrease was significant less at higher frequency. The decrease of polarization in the hysteresis loops corresponds to the leakage current components. Furthermore, the coercive field was virtually independent of the measurement frequency. It is concluded from these results that the large remanent polarizations measured in BFO films at RT are intrinsic ones based on ferroelectricity of the films.