Bistable states of ferroelectric hysteresis loops in a heteroepitaxial BaTiO3 thin film capacitor

Polarization vs voltage (P-V) hysteresis loops were investigated for a heteroepitaxial BaTiO3 thin film capacitor. Depending on amplitude of DC bias voltage which was superposed on alternative triangular waves, two types of P-V hysteresis loops were observed. They were characterized by the magnitude of the voltage shift from 0 V and named "on" and "off" states after their position. The transition between the two states exhibited hysteresis when the DC bias voltage was gradually increased and decreased. When intermediate amplitude of the DC bias voltage was applied, a "mixed" state appeared in the hysteresis loop, in which polarization reversal took place in two steps. Owing to the "on" state stabilized in the hysteresis loop, ferroelectric polarization of the heteroepitaxial capacitor was confirmed to be retained for longer than 4 h at 0 V.