Size-dependent polarization retention in ferroelectric BiFeO3 domain wall memories

Abstract

Reliable polarization retention in a single crystal-like ferroelectric thin film is crucial for the effective implementation of ferroelectric domain wall (DW) memories. This ensures that the saved information can be non-destructively read out by identifying the resistive state of the memory with a voltage signal below the coercive voltage (Vc) of the ferroelectric film. However, stabilizing a small volume of switched polarization for ultra-high-density information storage applications is still challenging due to its back-switching behavior at zero electric field. In this study, we investigated the polarization retention of ferroelectric BiFeO3 (BFO) thin film devices with size-variable Pt electrodes. With the scaling down of the device size, the switched polarizations became more susceptible to depolarization field and ferroelastic stress arising at the artificially created domain boundary. We found that BFO devices featuring a switched polarization area larger than 7 × 106 nm2 demonstrated both long-term polarization retention and a current rectification ratio of 4.5:1 induced by DW manipulation. As the device size decreases, the retention time of the switched polarization reduces gradually, which results in the disappearance of the device current due to the DW being eliminated by the back-switching of the polarization. A plot was created to illustrate the relationship between the current retention time and the switched polarization area on the surface of the BFO thin films. Furthermore, the unsustainable polarization retention facilitates a higher current rectification ratio of 48:1, which is suitable for non-destructive information readout with a voltage pulse larger than Vc in high-density ferroelectric DW memories.