Ultra-low resistance ohmic contacts in graphene field effect transistors

Abstract

We report on an experimental demonstration of graphene-metal ohmic contacts with contact resistance below 100 Ω µm. These have been fabricated on graphene wafers, both with and without hydrogen intercalation, and measured using the transmission line method. Specific contact resistivities of 3 × 10−7 to 1.2 × 10−8 Ω cm2 have been obtained. The ultra-low contact resistance yielded short-channel (source-drain distance of 0.45 µm) HfO2/graphene field effect transistors (FETs) with a low on-resistance (Ron) of 550 Ω µm and a high current density of 1.7 A/mm at a source-drain voltage of 1 V. These values represent state-of-the-art (SOA) performance in graphene-metal contacts and graphene FETs. This ohmic contact resistance is comparable to that of SOA high-speed III–V high electron mobility transistors.

Ultraviolet/ozone treatment to reduce metal-graphene contact resistance

“…To date, the best reported R c for lithographically defined contacts deposited onto exfoliated graphene flakes ranges from 200 Ω μm to 500 Ω μm. 3,4 R C for contacts formed to epitaxial graphene on SiC have been reported to be less than 100 Ω μm 5 and with specific contact resistivity (ρ c ) of order 10 -7 Ω cm 2 . 5,6 Reported values of R c for chemical vapor deposited (CVD) graphene typically range from 500 Ω μm to 1000 Ω μm.…”

“…3,4 R C for contacts formed to epitaxial graphene on SiC have been reported to be less than 100 Ω μm 5 and with specific contact resistivity (ρ c ) of order 10 -7 Ω cm 2 . 5,6 Reported values of R c for chemical vapor deposited (CVD) graphene typically range from 500 Ω μm to 1000 Ω μm. 7,8 Despite the technological attractiveness of CVD grown graphene, these contact resistances remain too large for most applications and are far from that reported for contacts to epitaxial graphene on SiC.…”

“…11 R c less than 100 Ω μm and specific contact resistivity less than 10 -7 Ω cm 2 have been reported for contacts formed to epitaxial graphene on SiC by other researchers, but details about device processing, importantly, contact formation are absent in the report. 5 Using a double contact device geometry R c of 200 Ω μm to 500 Ω μm on CVD graphene was reported. 12 Similar contact resistance was reported for metal contacts to CVD graphene by introducing an Al sacrificial layer.…”

Reverse degradation of nickel graphene junction by hydrogen annealing

“…[7][8][9][10][11][12][13][14][15][16][17] It has been argued that these variation can be attributed to the quality of graphene (exfoliated, CVD grown, epitaxial grown), the type of the contact (top or edge conduction), pre and post fabrication treatment as well as the underlying substrate. 18 Among all these metals, Pd metal contacts have been consistently reported to have a resistivity on the order of 100 ohms µm.…”

“…8,19 Ni and Ti contacts have also been reported to reach a lower contact resistivity but the values are strongly process specific. 20,13 The scarcity of Pd metal limits its application in large scale manufacturing, so it becomes critical to understand the origin of the resistance variation at nickel and titanium contacts.…”