Effects of interfacial charges on electrical asymmetry of epitaxial Bi₄Ti₃O₁₂ thin film capacitors

An apparently symmetric Pt/Bi₄Ti₃O₁₂/Pt capacitor structure was fabricated on MgO(001) substrate. Current-voltage measurement showed rectifying hysteresis and polarization-voltage measurement revealed strong imprint failure. To understand these interesting phenomena, capacitance-voltage (C-V) measurements were performed. By fitting the C-V data with a model which describes the Pt/BTO/Pt structure as a series circuit of three capacitors, built-in voltages at the top and the bottom interfaces were determined to be 1.1 V and 3.2 V, respectively. By applying the polarization-dependent permittivity model with the experimental values of the asymmetric built-in voltages, the current hysteresis could be described.