# Atomic‐Scale Mechanisms of Multi‐Resistance States in HfOx‐Based RRAM: Evolution of Atomic Electric Fields and Oxygen Vacancies

## TL;DR

The paper explains how atomic-level changes in hafnium oxide (HfOx) resistive RAM (RRAM) control different resistance states, which is important for improving memory-based computing.

## Contribution

The study reveals how oxygen vacancies and crystallographic rotations at the atomic scale determine resistive switching mechanisms in HfOx RRAM.

## Key findings

- Thermally driven m-phase rotation correlates with oxygen vacancy migration and resistance state transitions.
- Different resistance states (HRS, MRS, LRS) are linked to specific crystallographic orientations and vacancy distributions.
- Vacancy dynamics modify atomic electric fields, influencing conduction mechanisms like Schottky, Poole-Frenkel, and Ohmic transport.

## Abstract

The stability of multilevel resistive switching in HfOx‐based RRAM is crucial for enhancing matrix‐vector multiplication efficiency in computing‐in‐memory architectures, yet precise control over conductive filament formation is limited by an incomplete understanding of oxygen vacancy dynamics. Using advanced transmission electron microscopy (TEM) techniques, this study reveals key correlations among crystallographic orientation, oxygen vacancy distribution, and resistive switching mechanisms. Distinct m‐phase orientations govern resistance states: the High Resistance State (HRS) is characterized by a [101] orientation without oxygen vacancies; the Medium and Low Resistance States (MRS/LRS) exhibit a [011] orientation with selectively formed vacancies. Thermally driven m‐phase urotation ([101] ↔ [011]) facilitates oxygen vacancy migration, with vacancies preferentially occupying specific lattice sites. This alters the atomic electric fields around Hf atoms and modifies electron transport pathways. The distribution of vacancies directly controls conduction mechanisms: Schottky emission in HRS, Poole‐Frenkel emission in MRS, and Ohmic conduction in LRS, corresponding to increasing vacancy concentrations. These findings demonstrate that resistive states emerge from coupled processes: crystallographic rotation and vacancy formation reconstruct atomic electric fields, which in turn determine macroscopic conduction. This framework establishes design principles for RRAM optimization by demonstrating that precise control of thermal conductivity and voltage modulation can regulate vacancy dynamics, ensuring reliable multilevel switching.

Atomic‐scale mechanisms governing multilevel resistive switching in HfOx‐based RRAM are reveal through advanced TEM. Thermally driven m‐phase rotation ([101]↔[011]) enables selective oxygen vacancy migration, which reconstructs atomic electric fields and dictates conduction—from Schottky/Poole‐Frenkel emission to Ohmic transport. This insight establishes design principles for reliable computing‐in‐memory devices.