Asymmetric switching of ferroelectric polarization in a heteroepitaxial BaTiO3 thin film capacitor

Asymmetric switching of ferroelectric polarization was measured and analyzed for a heteroepitaxial BaTiO3 thin film of 58 nm thickness. The BaTiO3 film prepared on a SrRuO3/SrTiO3 substrate by radio-frequency magnetron sputtering has a c-axis oriented normal to the surface which is 3% longer than that of the bulk due to lattice misfit between SrRuO3 and BaTiO3. When positive and negative voltage pulses of the same amplitude were sequentially applied, asymmetric responses were observed in the transient current, Although the switching charge densities Q(sw) were the same for both the polarities, the switching time t(s) was longer and the peak current i(max) was smaller for the positive response. From the analyses of the transient current, the asymmetric switching of polarization was attributed to the discrepancy in coercive voltages V-c between polarities.