Voltage shift phenomena in a heteroepitaxial BaTiO3 thin film capacitor

Voltage shift phenomena of the hysteresis loop were characterized for a $c$ -axis oriented heteroepitaxial ${\mathrm{BaTiO}}_{\mathrm{3}}$ film by means of switching current measurements using various types of pulse sequences. During application of voltage, the hysteresis loop gradually shifted along the voltage axis according to the polarity of the voltage. Even after the application of voltage, while the top and bottom electrodes were short-circuited, the hysteresis loop continued to move. Under certain conditions, a part of the hysteresis loop shifted back, whereas the rest shifted forward. These results were explained, assuming that there is a nonswitching layer between the ferroelectric layer and the bottom electrode, and that the discontinuity of polarization can be compensated by injection of negative charges from the electrode. It was suggested that the nonswitching layer is possibly formed by relaxation of lattice misfit strain in the heteroepitaxial ferroelectric thin film.