Immunity to Scaling in MoS2 Transistors Using Edge Contacts

TL;DR

This paper demonstrates that edge contacts to MoS2 transistors maintain high performance even at very small contact lengths, offering a solution to the contact scaling problem in 2D material-based transistors.

Contribution

The study introduces a novel edge contact method for MoS2 transistors that is immune to contact length scaling, outperforming traditional top contacts in efficiency and performance.

Findings

Edge contacts maintain performance down to 20 nm contact length.

Cr-MoS2 interface shows superior bonding and performance.

Edge contacts achieve effective contact length of ~1 nm with high carrier injection.

Abstract

Atomically thin two-dimensional (2D) materials are promising candidates for sub-10 nm transistor channels due to their ultrathin body thickness, which results in strong electrostatic gate control. Properly scaling a transistor technology requires reducing both the channel length (distance from source to drain) and the contact length (distance that source and drain interface with semiconducting channel). Contact length scaling remains an unresolved epidemic for transistor scaling, affecting devices from all semiconductors, from silicon to 2D materials. Here, we show that clean edge contacts to 2D MoS2 provide immunity to the contact-scaling problem, with performance that is independent of contact length down to the 20 nm regime. Using a directional ion beam, in situ edge contacts of various metal-MoS2 interfaces are studied. Characterization of the intricate edge interface using cross-sectional electron microscopy reveals distinct morphological effects on the MoS2 depending on its thickness, from monolayer to few-layer films. Chromium is found to outperform other metals in the edge contact scheme, which is attributed to the shorter Cr-MoS2 bond length. Compared to scaled top contacts with 20 nm contact length, in situ edge contacts yield better performance with an effective contact length of ~ 1 nm and 18 times higher carrier injection efficiency. The in situ edge contacts also exhibit ~8 times higher performance compared to the best-reported edge contacts. Our work provides experimental evidence for a solution to contact scaling in transistors, using 2D materials with clean edge contact interfaces, opening a new way of designing devices with 2D materials.