Impedance Spectroscopy on Hafnium Oxide‐Based Memristive Devices

Memristive devices for neuromorphic computing have been attracting ever growing attention over the last couple of years. In neuromorphic elec-tronics, 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, imped-ance 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 inter-preted by the charging and discharging of double positively charged oxygen vacancies 22++VVOO≈ 0.9 eV. The results of the impedance analysis are translated into a more general model for memristive devices to map the physical pro-cesses during switching.