Nanoscale imaging of He-ion irradiation effects on amorphous TaO$_x$ toward electroforming-free neuromorphic functions

TL;DR

This study uses advanced microscopy techniques to investigate how helium ion irradiation affects amorphous TaO$_x$, revealing insights into resistive switching mechanisms and enabling low-power, electroforming-free neuromorphic device functions.

Contribution

It introduces a multimodal experimental framework combining sMIM and CL microscopy to probe resistive switching in amorphous TaO$_x$, and demonstrates low-power electroforming-free control via He-ion irradiation.

Findings

He-ion irradiation modifies bond nature but maintains stability at low doses.

Electroforming can be achieved with less than 20 nW power.

He-irradiation induces metallic states only at high damage levels.

Abstract

Resistive switching in thin films has been widely studied in a broad range of materials. Yet the mechanisms behind electroresistive switching have been persistently difficult to decipher and control, in part due to their non-equilibrium nature. Here, we demonstrate new experimental approaches that can probe resistive switching phenomena, utilizing amorphous TaO$_x$ as a model material system. Specifically, we apply Scanning Microwave Impedance Microscopy (sMIM) and cathodoluminescence (CL) microscopy as direct probes of conductance and electronic structure, respectively. These methods provide direct evidence of the electronic state of TaO$_x$ despite its amorphous nature. For example CL identifies characteristic impurity levels in TaO$_x$, in agreement with first principles calculations. We applied these methods to investigate He-ion-beam irradiation as a path to activate conductivity of materials and enable electroforming-free control over resistive switching. However, we find that even though He-ions begin to modify the nature of bonds even at the lowest doses, the films conductive properties exhibit remarkable stability with large displacement damage and they are driven to metallic states only at the limit of structural decomposition. Finally, we show that electroforming in a nanoscale junction can be carried out with a dissipated power of < 20 nW, a much smaller value compared to earlier studies and one that minimizes irreversible structural modifications of the films. The multimodal approach described here provides a new framework toward the theory/experiment guided design and optimization of electroresistive materials.