New Approaches and Observations in Scaled Contacts for 2D FETs

Atomically thin 2D crystals are promising channel materials for extremely scaled field-effect transistors (FETs). For devices at the scaled regime, both channel and contact length must be scaled, with channel length being the distance from source to drain contacts and contact length being the length of the source/drain covering the 2D semiconductor channel. Contacting 2D materials at these scaled contact lengths (< 30 nm) has rarely been pursued or studied in depth. Moreover, the device community has not yet determined how contacts can be scaled without causing significant degradation in device performance; i.e., how long is the transfer length, below which current crowding effects appear? Here, we demonstrate new measurement approaches and results for determining the transfer length of MoS₂ FETs by physically scaling the contact length. We found that, contrary to previous reports, top contacts can be scaled to ~20 nm without obvious degradation in transistor performance. Our data from measurements of over 100 devices with different contact lengths statistically imply that contact resistance variation increases in the scaled contact regime. Our work illustrates the impact of current crowding in scaled contacts and the ultimate scalability of metal-2D contact interfaces.