Graphene has generated enormous research interest because of its unique physical and electronic properties. In particular, a large part of the research interests and activities arise from the high intrinsic carrier mobility and saturation velocity in graphene that may lead to higher-frequency electronic devices/circuits than can be achieved by conventional semiconductor materials. Here we present the top-gated graphene transistors fabricated on two-inch graphene wafer.

 

Graphene was epitaxially grown on the Si face of a high-purity semi-insulating SiC 4H(0001) wafer by thermal decomposition, yielding a film of 1-2 layers of graphene over the entire wafer. The as-grown graphene film possesses an electron (n-type) carrier density of ~ 3x1012 cm-2 and a Hall-effect mobility between 1000–1500 cm2/V.s. In order to preserve the intrinsic mobility of graphene in the top-gated device structure, an interfacial polymer layer was spin-coated on the graphene prior to the oxide deposition. The carrier mobility of top-gated Hall bar devices varied between 900-1520 cm2/V.s across the two-inch wafer, indicating that little degradation in graphene mobility.

 

The cutoff frequency fTis obtained from the high-frequency S-parameters measurements, which signifies the highest frequency at which a transistor can propagate an electrical signal. For a gate length of 550 nm, the measured fT ranges between 20 to 53 GHz. For a shorter gate length of 240 nm, fT as high as 100 GHz was measured. This 100 GHz cutoff frequency is the highest speed achieved to date for any type of graphene devices, including exfoliated and CVD -grown graphene. Further enhancement in the device performance is expected to be achieved by continued improvements in the electrical characteristics of epitaxial graphene and the gate length scaling.

 

*In collaboration with K. Jenkins, D. Farmer, C. Dimitrakopoulos, H.-Y. Chiu, A. Valdes-Garcia, A. Grill, and P. Avouris.