Schottky-to-Ohmic switching in ferroelectric memristors based on semiconducting Hf0.93Y0.07O2 thin films

Abstract

We demonstrate resistive switching and memristive behavior in devices consisting of ultrathin (4.5 nm) semiconducting, epitaxial ferroelectric Hf0.93Y0.07O2 (YHO) films on La0.7Sr0.3MnO3-buffered, Nb-doped SrTiO3 single crystal substrates with Au top electrodes. Unlike the tunneling-driven current–voltage characteristics of ferroelectric tunnel junctions which utilize ultrathin insulating (fully depleted) ferroelectric films, the semiconducting nature of our YHO films, i.e., the presence of free charge carriers introduced by Y doping, results in radically different current–voltage characteristics. Current–voltage measurements indicate a polarization-modulated transition from Schottky-barrier-controlled charge transport to Ohmic conduction in the YHO devices, which results in a large on/off ratio of up to 540. Moreover, voltage pulse train measurements reveal a broad range of accessible resistance states, which indicates the memristive behavior of the devices. Our results represent an important step toward the development of future nonvolatile memory and brain-inspired neuromorphic computing applications based on ultrathin semiconducting ferroelectric films.