Direct Imaging of Nanoscale Conductance Evolution in Ion-Gel-Gated Oxide Transistors

TL;DR

This study uses cryogenic microwave impedance microscopy to visualize nanoscale conductance changes in electrolyte-gated oxide transistors, revealing local electronic variations during the metal-insulator transition.

Contribution

It introduces a high-resolution imaging technique for real-space mapping of conductance in electrolyte-gated transistors, overcoming previous microscopic limitations.

Findings

Visualized spatial conductance evolution during transition

Detected local conductance fluctuations and inhomogeneities

Showed uneven conductance distribution under bias

Abstract

Electrostatic modification of functional materials by electrolytic gating has demonstrated a remarkably wide range of density modulation, a condition crucial for developing novel electronic phases in systems ranging from complex oxides to layered chalcogenides. Yet little is known microscopically when carriers are modulated in electrolyte-gated electric double-layer transistors (EDLTs) due to the technical challenge of imaging the buried electrolyte-semiconductor interface. Here, we demonstrate the real-space mapping of the channel conductance in ZnO EDLTs using a cryogenic microwave impedance microscope. A spin-coated ionic gel layer with typical thicknesses below 50 nm allows us to perform high resolution (on the order of 100 nm) sub-surface imaging, while maintaining the capability of inducing the metal-insulator transition under a gate bias. The microwave images vividly show the spatial evolution of channel conductance and its local fluctuations through the transition, as well as the uneven conductance distribution established by a large source-drain bias. The unique combination of ultra-thin ion-gel gating and microwave imaging offers a new opportunity to study the local transport and mesoscopic electronic properties in EDLTs.