Injection charge dynamics on the Pb(Zr_0.52Ti_0.48)O₃surface by scanning probe microscopy

The origin of an injected charge and its temperature dependence in ferroelectric Pb(Zr0.52Ti0.48)O3 (PZT) thin films is studied by multimode scanning probe microscopy. During the poling process in scanning probe microscope (SPM) measurement, which is a local bias applied by using a conductive tip on a film's surface to induce polarization orientation, a strong charge injection is always observed in oxide ferroelectric films; therefore, the surface potential is dominated by injection charge rather than polarization and screening charge. The surface potential shows an increase with the increase in the applied bias and saturation at a higher bias, which is much higher than the coercive field in PZT films. The positive surface potential shows a clear increase after oxygen plasma treatment, suggesting that the injection behavior is significantly enhanced. Subsequent heating could recover the surface condition to the initial state. Charge injection could be weakened but could not be completely eliminated by heat treatment. The current results suggest that charge injection behavior could not be easily relaxed, and a careful control of the localized poling process using an SPM conductive tip is required especially for studying the charge state on the surfaces of ferroelectric thin films.