Investigation of the Polarization Dependence of the Transient Current in Polycrystalline and Epitaxial Pb(Zr, Ti)O3 Thin Films

The polarization dependence of the current in epitaxial and polycrystalline (with conductive grain boundaries) Pb(Zr, Ti)O-3 (PZT) films is studied using direct-current (dc) measurements and scanning spreading current microscopy. Both methods show identical results in micro-and nanoscale ranges. The current response from the film to the applied bias contains a long relaxation component that depends on the bias rise rate and polarization direction, exhibiting current peaks near the coercive force value. The polarization dependences of the current for polycrystalline and epitaxial films are found to be fundamentally different. The current of the polycrystalline film is much higher when the bias is directed against the polarization, whereas the current of the epitaxial film is higher if the bias and polarization directions coincide. All films exhibit current hysteresis of non-ferroelectric (clockwise) direction with decreasing bias. It is also shown that the polarization dependences of the transient current in both polycrystalline and epitaxial films are similar to the polarization dependence of the photovoltaic current in these films.