The effect of Ta oxygen scavenger layer on HfO$_2$-based resistive switching behavior: thermodynamic stability, electronic structure, and low-bias transport

TL;DR

This study uses density functional theory to analyze how a Ta oxygen scavenger layer affects the thermodynamic stability, electronic structure, and low-bias transport in HfO₂-based resistive switching devices, revealing mechanisms for performance enhancement.

Contribution

It provides a fundamental understanding of how Ta scavenger layers modify heterostructure properties, improving device performance and stability in resistive memory applications.

Findings

Ta insertion lowers formation energy of low-resistance states

Ta layer reduces Schottky barrier height in high-resistance state

Conductance becomes less sensitive to oxygen distribution with Ta layer

Abstract

Reversible resistive switching between high-resistance and low-resistance states in metal-oxide-metal heterostructures makes them very interesting for applications in random access memories. While recent experimental work has shown that inserting a metallic "oxygen scavenger layer" between the positive electrode and oxide improves device performance, the fundamental understanding of how the scavenger layer modifies heterostructure properties is lacking. We use density functional theory to calculate thermodynamic properties and conductance of TiN/HfO$_2$/TiN heterostructures with and without Ta scavenger layer. First, we show that Ta insertion lowers the formation energy of low-resistance states. Second, while the Ta scavenger layer reduces the Schottky barrier height in the high-resistance state by modifying the interface charge at the oxide-electrode interface, the heterostructure maintains a high resistance ratio between high- and low-resistance states. Finally, we show that the low-bias conductance of device on-states becomes much less sensitive to the spatial distribution of oxygen removed from the HfO$_2$ in the presence of the Ta layer. By providing fundamental understanding of the observed improvements with scavenger layers, we open a path to engineer interfaces with oxygen scavenger layers to control and enhance device performance. In turn, this may enable the realization of a non-volatile low-power memory technology with concomitant reduction in energy consumption by consumer electronics and significant benefits to society.