Impedance Spectroscopy on Hafnium Oxide‐Based Memristive Devices

Abstract

AbstractMemristive devices for neuromorphic computing have been attracting ever growing attention over the last couple of years. In neuromorphic electronics, memristive devices with multi‐level resistance states are required to accurately reproduce synaptic weights. Here, a memristive device based on a multilayer oxide system (Nb/NbOx/Al2O3/HfO2/Au), which features a filamentary‐free, homogenous interfacial resistive switching mechanism, is investigated. To gain a deeper insight into the switching mechanism, impedance spectroscopy (ImpSpec), X‐ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM) are exploited. While this work focuses on the analysis of impedance and current‐voltage characteristics, XPS and TEM investigations can be found in a companion paper (Zahari et al.). In the course of this investigation, potentiodynamic impedance spectroscopy (PD‐ImpSpec) and time resolved impedance spectroscopy (TR‐ImpSpec) in combination with transient analysis are used. Evidence is presented of switching kinetics at voltages above 2.1 V directly related to changes in Schottky barrier resistance. These switching kinetics can in turn be interpreted by the charging and discharging of double positively charged oxygen vacancies ≈ 0.9 eV. The results of the impedance analysis are translated into a more general model for memristive devices to map the physical processes during switching.