Stabilizing Schottky-to-Ohmic Switching in HfO2-based Ferroelectric Films via Electrode Design

Abstract

The discovery of ferroelectric phases in HfO2-based films has reignited interest in ferro- electrics and their application in resistive switching (RS) devices. This study investigates the pivotal role of electrodes in facilitating the Schottky-to-Ohmic transition (SOT) observed in devices consisting of ultrathin epitaxial ferroelectric Hf0.93Y0.07O2 (YHO) films deposited on La0.67Sr0.33MnO3-buffered Nb-doped SrTiO3 (NbSTO|LSMO) with Ti|Au top electrodes. Our findings indicate combined filamentary RS and ferroelectric switching occurs in devices with designed electrodes, having an ON/OFF ratio of over 100 during about 105 cycles. Trans- port measurements of modified device stacks show no change in SOT when the ferroelectric YHO layer is replaced with an equivalent hafnia-based layer, Hf0.5Zr0.5O2 (HZO). However, incomplete SOT is observed for variations in the top electrode thickness or material, as well as LSMO electrode thickness. This underscores the importance of employing oxygen-reactive electrodes and a bottom electrode with significant depletion regions to stabilize SOT. Our findings provide valuable insights for enhancing the performance of ferroelectric RS devices through integration with filamentary RS mechanism.