Nanoscale Imaging and Control of Volatile and Non‐Volatile Resistive Switching in VO₂

Abstract

Control of the metal‐insulator phase transition is vital for emerging neuromorphic and memristive technologies. The ability to alter the electrically driven transition between volatile and non‐volatile states is particularly important for quantum‐materials‐based emulation of neurons and synapses. The major challenge of this implementation is to understand and control the nanoscale mechanisms behind these two fundamental switching modalities. Here, in situ X‐ray nanoimaging is used to follow the evolution of the nanostructure and disorder in the archetypal Mott insulator VO2 during an electrically driven transition. Our findings demonstrate selective and reversible stabilization of either the insulating or metallic phases achieved by manipulating the defect concentration. This mechanism enables us to alter the local switching response between volatile and persistent regimes and demonstrates a new possibility for nanoscale control of the resistive switching in Mott materials.

Transverse barrier formation by electrical triggering of a metal-to-insulator transition

“…Instead, an unusual out-of-equilibrium phase separation is favored: a transverse insulating barrier divides the conducting matrix and blocks the electric current flow. This is reciprocal to the resistive switching from an insulator into a metal (for example, in vanadium oxides 22 – 24 , 48 ), which occurs by the formation of longitudinal percolating metallic filaments. The appearance of a voltage-induced insulating barrier proves that the LSMO device undergoes an abrupt resistive switching on a microscopic level, from the metallic into the insulating phase, even though the global I–V curve of the entire device displays smooth, gradual, low- to high-resistance evolution.…”

Quantum materials for energy-efficient neuromorphic computing

“…For example, vanadium oxides can be triggered with external voltage, current source, or thermal source and the formation of filament can be optically mapped such as in-situ Xray nanoimaging. 163,206 It is not a trivial task to integrate the driving excitation system for the phase transition and the analysis tools. When using a Raman spectrometer to analyze a temperature-driven device, careful design of the thermal chamber for the sample is necessary.…”

Embedded metallic nanoparticles facilitate metastability of switchable metallic domains in Mott threshold switches

“…Due to the extreme sensitivity of the electronic phase transition between competing phases, a subtle perturbation by external stimuli can abruptly transform an existing phase into a different electronic phase, leading to steep modulation of the electrical properties [7][8][9][10][11][12] . A characteristic phenomenon during the first order metal-insulator transition is the appearance of phase separation with metallic and insulating domains with inhomogeneous distributions down to a few nanometers 11,[13][14][15][16][17] . The existence of phase separation implies that the resistance modulation occurs through a series of percolation transforming parts of the system from one phase to the other 2,11,[13][14][15][16][17][18][19] .…”

“…A characteristic phenomenon during the first order metal-insulator transition is the appearance of phase separation with metallic and insulating domains with inhomogeneous distributions down to a few nanometers 11,[13][14][15][16][17] . The existence of phase separation implies that the resistance modulation occurs through a series of percolation transforming parts of the system from one phase to the other 2,11,[13][14][15][16][17][18][19] . This percolative nature allows for an inhomogeneous transitional state where both metallic and insulating phases coexist; the dynamics of percolative domains in the intermediate state determines the macroscopic properties related to phase transition in quantum materials 2,11,[13][14][15][16][17][18][19] .…”

“…In addition to temperature as an external stimulus, the insulator-to-metal transition (IMT) can be electrically stimulated on a subnanosecond time scale by applying an external voltage on two-terminal VO 2 devices if a threshold voltage (V th ) is exceeded 2,7,14,[16][17][18][23][24][25][26] . A reverse metal-to-insulator transition (MIT) can promptly occur once the electrical stimulus is removed.…”