Ferroresistive Diode Currents in Nanometer-Thick Cobalt-Doped BiFeO₃ Films for Memory Applications

Ferroelectric diodes hold significant promise for potential applications in nonvolatile memories and logic devices. The nondestructive readout of binary information can be achieved by using a bipolar switching with two different conductances under two opposite polarizations in a ferroelectric diode, which exhibits ultrahigh density and ultrafast operating speed. However, the diode current is limited because most ferroelectrics have wide band gaps. Therefore, in modern micromemory circuits, obtaining a sufficient ferroresistive diode current to detect the status of memory stably is a major challenge. Herein, a high current-intensity resistive switching behavior in nanometer-thick BiFe0.9Co0.1O3 films is reported. Epitaxial films were prepared on a (00l) Nb/SrTiO3 single-crystal substrate via the chemical solution epitaxial deposition method. The conductance of the BiFeO3 diode improved by up to 200 times that of the original. This improvement can be attributed to the bandgap decrease in ferroelectric film induced by Co doping, as confirmed by spectrophotometry and first-principles calculations. This device shows a stable bipolar resistive switching feature, a satisfactory switching ratio of ∼103, good data retention, and antifatigue characteristics for up to 107 cycles. The results are useful in exploring the potential applications of a ferroelectric diode in RRAM.