# Full control of solid-state electrolytes for electrostatic gating

## TL;DR

This paper demonstrates the use of solid-state electrolytes for ionic gating in FETs, achieving high control, reproducibility, and enabling advanced surface and spectroscopic techniques.

## Contribution

It identifies the causes of spurious phenomena in solid-state electrolyte gating and demonstrates high-performance, reproducible transistors with novel capabilities such as ionic-gate spectroscopy and independent double gating.

## Key findings

- Achieved high gate capacitance of 20-50 μF/cm²
- Demonstrated gate-induced superconductivity in MoS₂
- Enabled surface-sensitive techniques in ionic gating

## Abstract

Ionic gating is a powerful technique to realize field-effect transistors (FETs) enabling experiments not possible otherwise. So far, ionic gating has relied on the use of top-electrolyte gates, which pose experimental constraints and make device fabrication complex. Promising results obtained recently in FETs based on solid-state electrolytes remain plagued by spurious phenomena of unknown origin, preventing proper transistor operation, and causing limited control and reproducibility. Here we explore a class of solid-state electrolytes for gating (Lithium-ion conducting glass-ceramics, LICGCs), identify the processes responsible for the spurious phenomena and irreproducible behavior,and demonstrate properly functioning transistors exhibiting high density ambipolar operation with gate capacitance of ~20-50 $\mu$F/cm$^2$ (depending on the polarity of the accumulated charges). Using two-dimensional semiconducting transition-metal dichalcogenides we demonstrate the ability to implement ionic-gate spectroscopy to determine the semiconducting bandgap, and to accumulate electron densities above 10$^{14}$ cm$^{-2}$, resulting in gate-induced superconductivity in MoS$_2$ multilayers. As LICGCs are implemented in a back-gate configuration, they leave the surface of the material exposed, enabling the use of surface-sensitive techniques (such as scanning tunneling microscopy and photoemission spectroscopy) impossible so far in ionic-liquid gated devices. They also allow double ionic gated devices providing independent control of charge density and electric field.