Reducing Contact Resistance in Graphene Devices through Contact Area Patterning

Abstract

Performance of graphene electronics is limited by contact resistance associated with the metal-graphene (M-G) interface, where unique transport challenges arise as carriers are injected from a 3D metal into a 2D-graphene sheet. In this work, enhanced carrier injection is experimentally achieved in graphene devices by forming cuts in the graphene within the contact regions. These cuts are oriented normal to the channel and facilitate bonding between the contact metal and carbon atoms at the graphene cut edges, reproducibly maximizing "edge-contacted" injection. Despite the reduction in M-G contact area caused by these cuts, we find that a 32% reduction in contact resistance results in Cu-contacted, two-terminal devices, while a 22% reduction is achieved for top-gated graphene transistors with Pd contacts as compared to conventionally fabricated devices. The crucial role of contact annealing to facilitate this improvement is also elucidated. This simple approach provides a reliable and reproducible means of lowering contact resistance in graphene devices to bolster performance. Importantly, this enhancement requires no additional processing steps.

Graphene field effect transistors with niobium contacts and asymmetric transfer characteristics

“…Selected graphene monolayers were contacted using electron [14] and other factors may contribute the transparency of the interface, so that graphene defectiveness may not necessarily be detrimental. Reduction of the specific contact resistance has been achieved by O2 plasma damaging [15] or by intentional pitting [16] or cutting [17] of graphene in the contact region.…”

Contact resistance in graphene channel transistors

“…Theoretical reports estimated that the contact resistivity could be as low as 10 to 10 3 times the facial contact based on a quantum tunneling process [57]. Very recently, contact modules considering the edge contact resistance were developed [80]. The proposed contact module results in an improvement of approximately 20~60% compared to the conventional method involving a lift-off process.…”

Approaches to Reduce the Contact Resistance by the Formation of Covalent Contacts in Graphene Thin Film Transistors

“…It is notable that the cuts are not extended to the end of graphene, which would result in a comb pattern. Smith et al fabricated the rail-patterned graphene device using different number of cuts to increase the perimeter length of graphene for their study on the device performance based on the amount of cuts made [53]. Their TLM measurements yielded a contact resistance of 125 Ω·μm post-anneal with 10 cuts under Cu contact, compared to 184 Ω·μm post-anneal without any patterns, which proves that the patterns provide a better device performance via covalent contacts.…”

“…Furthermore, their study showed that as the perimeter length increased, more areas of graphene become available for covalent contacts, and a decrease in the total resistance of the device post-anneal was first seen. Yet, as the number of cuts increased beyond 8, an upturn of the resistance was shown because extreme narrowing of the width of the graphene nanoribbons by making too many cuts had led to quantization effects that impeded carrier transfer at the interface [53]. Because this pattern works best under optimal conditions, in which the perimeter length is kept as large as possible while maintaining a large enough graphene nanoribbon width, a significant limitation exists for this device pattern.…”