ISBN 9783843931656

978-3-8439-3165-6, Reihe Elektrotechnik

Astrid Marchewka
A numerical simulation model of valence-change-based resistive switching

233 Seiten, Dissertation Rheinisch-Westfälische Technische Hochschule Aachen (2017), Softcover, B5

Zusammenfassung / Abstract

Due to superior scalability and performance, nanoscale resistive switches based on the valence-change mechanism are considered promising candidates for future nonvolatile memory and logic applications. The switching mechanism in these metal-oxide-metal structures is widely acknowledged to rely on temperature-accelerated migration of donors, such as oxygen vacancies, inside the oxide layer and a concomitant change in the electronic barrier at the Schottky-like metal-oxide interface.

On the way towards a sound understanding of the underlying physics, the development of comprehensive simulation models is still a key challenge. In this work, a numerical model of valence-change-based resistive switching is introduced. It is based on a finite-volume formulation of the coupled electronic and ionic transport in the device. Associated physical processes like thermionic emission and tunnelling of electrons, Joule heating, incomplete dopant ionization, and oxygen exchange at the electrodes are also captured.

The simulation model is employed to investigate a variety of resistive-switching phenomena. One-dimensional simulations assuming static donor profiles are performed to explore the influence of various physical parameters on the current-density-voltage relations, and the switching mechanism of Schottky-barrier modification induced by changes in donor density is evaluated. Simulations involving donor migration are demonstrated to result in bipolar switching with an abrupt set and a gradual reset transition for devices with asymmetric barriers. It is shown that a transition to complementary switching occurs when reducing the asymmetry of the barriers. The nonlinear set kinetics is evaluated for different parameters, confirming the experimentally observed universal relationship between the dissipated power and the set times.

Two-dimensional axisymmetric simulations are employed to investigate the reset process in TaOx-based memory cells, identifying the gradual nature to rely on the interaction between ionic drift and diffusion processes that approach equilibrium. Simulations of electroforming reveal a dependence of filament growth direction and post-forming resistance state on the rate of oxygen exchange vs. the rate of ionic transport inside the oxide layer. Finally, simulations of potential profiles of pristine Pt/Fe:STO/Nb:STO structures suggest that acceptor-type dopants at the Nb:STO electrode interface significantly impact the local field distribution.