Local On/Off Currents in BiFeO3 Thin Films Modulated by Bipolar Polarization Orientations

Nonvolatile memories on the basis of tunneling junctions of ferroelectric ultrathin-film barriers make use of resistance switching between high and low conductance states upon polarization reversal, which facilitates the nondestructive readout of the binary information within a tiny memory cell. The apparent electroresistance effect for the generation of a large on/off current ratio depends on the modulation of the tunneling barrier height in two opposite polarization orientations due to asymmetric finite screening lengths of top and bottom electrodes, where the direct tunneling current attenuates quickly with enhanced film thickness. To break through the atomistic thickness requirement of the tunneling junction, we separately observed the same electroresistance effect in a semiconducting BiFeO3 film with the thickness of 120 nm. Its working mechanism depends on the formation of a ferroelectric diode for the film in contacts with top and bottom electrodes, where the polarity of diode junction can be switched by polarization reversal.