In depth nano spectroscopic analysis on homogeneously switching double barrier memristive devices

TL;DR

This study uses advanced nano spectroscopic techniques to analyze the microstructure and conduction mechanisms of a homogeneously switching double barrier memristor, revealing unexpected oxidation and structural deviations.

Contribution

It provides a detailed chemical and structural analysis of the memristor, highlighting the robustness of its design despite deviations from the intended layout.

Findings

Significant oxidation of the bottom electrode detected

Small oxygen vacancy concentration in Al oxide tunnel barrier

Structural deviations do not impair device functionality

Abstract

Memristors based on a double barrier design have been analysed by various nano spectroscopic methods to unveil details about its microstructure and conduction mechanism. The device consists of an AlOx tunnel barrier and a NbOy/Au Schottky barrier sandwiched between Nb bottom electrode and Au top electrode. As it was anticipated that the local chemical composition of the tunnel barrier, i.e. oxidation state of the metals as well as concentration and distribution of oxygen ions, have a major influence on electronic conduction, these factors were carefully analysed. A combined approach was chosen in order to reliably investigate electronic states of Nb and O by electron energy-loss spectroscopy as well as map elements whose transition edges exhibit a different energy range by energy-dispersive X-ray spectroscopy like Au and Al. The results conclusively demonstrate significant oxidation of the bottom electrode as well as a small oxygen vacancy concentration in the Al oxide tunnel barrier. Possible scenarios to explain this unexpected additional oxide layer are discussed and kinetic Monte Carlo simulations were applied in order to identify its influence on conduction mechanisms in the device. In light of the strong deviations between observed and originally sought layout, this study highlights the robustness in terms of structural deviations of the double barrier memristor device.