Improved Contacts to MoS2 Transistors by Ultra-High Vacuum Metal Deposition

TL;DR

This study demonstrates that ultra-high vacuum metal deposition significantly reduces contact resistance in MoS2 transistors, enabling smaller device dimensions and improved stability, with detailed modeling providing insights for further scaling.

Contribution

It introduces a systematic analysis of MoS2 contacts with ultra-high vacuum gold deposition, revealing lower contact resistance and providing a model to understand contact contributions for device scaling.

Findings

Ultra-high vacuum gold deposition reduces contact resistance by three times.

Contact resistance remains stable over four months.

Contact transfer length is approximately 35 nm at 300 K.

Abstract

The scaling of transistors to sub-10 nm dimensions is strongly limited by their contact resistance (Rc). Here we present a systematic study of scaling MoS2 devices and contacts with varying electrode metals and controlled deposition conditions, over a wide range of temperatures (80 to 500 K), carrier densities (10^12 to 10^13 1/cm^2), and contact dimensions (20 to 500 nm). We uncover that Au deposited in ultra-high vacuum (~10^-9 Torr) yields three times lower Rc than under normal conditions, reaching 740 Ohm-um and specific contact resistivity 3x10^-7 Ohm.cm2, stable for over four months. Modeling reveals separate Rc contributions from the Schottky barrier and the series access resistance, providing key insights on how to further improve scaling of MoS2 contacts and transistor dimensions. The contact transfer length is ~35 nm at 300 K, which is verified experimentally using devices with 20 nm contacts and 70 nm contact pitch (CP), equivalent to the "14 nm" technology node.