# Meeting the Scaling Challenge for Post-Silicon Nanoelectronics using CaF2 Insulators

## TL;DR

This paper demonstrates the use of crystalline CaF2 as a scalable, ultra-thin insulator for 2D MoS2 transistors, achieving low leakage and high performance, addressing key challenges in post-silicon nanoelectronics.

## Contribution

It introduces CaF2 as a high-quality, epitaxial insulator compatible with 2D semiconductors, enabling scalable, ultra-thin gate dielectrics for nanoelectronic devices.

## Key findings

- CaF2 forms a quasi van der Waals interface with 2D semiconductors.
- Achieved sub-1 nm equivalent oxide thickness with low leakage.
- Devices show record-small hysteresis and competitive performance.

## Abstract

Two-dimensional (2D) semiconductors have been suggested both for ultimately-scaled field-effect transistors (FETs) and More-than-Moore nanoelectronics. However, these targets can not be reached without accompanying gate insulators which are scalable into the nanometer regime. Despite the considerable progress in the search for channel materials with high mobilities and decent bandgaps, finding high-quality insulators compatible with 2D technologies has remained a challenge. Typically used oxides (e.g. SiO2, Al2O3 and HfO2) are amorphous when scaled, while two-dimensional hBN exhibits excessive gate leakages. To overcome this bottleneck, we extend the natural stacking properties of 2D heterostructures to epitaxial fluorite (CaF2), which forms a quasi van der Waals interface with 2D semiconductors. We report scalable single-layer MoS2 FETs with a crystalline CaF2 insulator of about 2 nm thickness, which corresponds to an equivalent oxide thickness of less than 1 nm. While meeting the stringent requirements of low leakage currents, our devices exhibit highly competitive performance and record-small hysteresis. As such, our results present a breakthrough for very large scale integration towards commercially competitive nano-electronic devices.