Coexistence of unipolar and bipolar resistive switching in BiFeO3 and Bi0.8Ca0.2FeO3 films

Ferroelectric BiFeO3 and paraelectric Bi0.8Ca0.2FeO3 polycrystalline films were prepared to study the dependence of resistive switch on defect density. With defect density and the corresponding leakage current increasing, current-voltage loops allow four different types, i.e., overlapping, hysteresis without memory effect, bipolar resistive switch, and unipolar resistive switch. The first three types can transform to the last one, once electroforming introduces enough charged defects to films and the resistance monotonically increases to a certain value. Unipolar resistive switch is due to conductive filamentary type and can be treated as an especial electroforming process. Furthermore, its high resistance status allows the second or third type at low voltage region. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4716867]