Imprint failures and asymmetric electrical properties induced by thermal processes in epitaxial Bi₄Ti₃O₁₂ thin films

Epitaxial Bi₄Ti₃O₁₂ (BTO) thin films were deposited on MgO(001) substrates using Pt layers as top and bottom electrodes. In spite of the apparently symmetric capacitor structure, polarization-voltage measurements revealed strong imprint failures and current-voltage measurements showed rectifying behaviors. Imprint pulse tests with a 5 V dc bias and post-annealing treatments suggested that the asymmetric behaviors should be due to interfacial states induced by thermal processes. To probe the interfacial states, 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 composed of three capacitors, built-in voltages at the top and the bottom interfaces could be determined. Difference in the built-in voltages could explain the imprint failures and the rectifying behaviors. The interfacial states in the BTO capacitors were controlled by varying electrode materials.