Graphene Field-Effect Transistors With High Extrinsic <inline-formula> <tex-math notation="LaTeX">${f}_{T}$</tex-math> </inline-formula> and <inline-formula> <tex-math notation="LaTeX">${f}_{\mathrm{max}}$</tex-math> </inline-formula>

Abstract

In this work, we report on the performance of graphene field-effect transistors (GFETs) in which the extrinsic transit frequency (f T) and maximum frequency of oscillation (fmax) showed improved scaling behavior with respect to the gate length (Lg). This improvement was achieved by the use of high-quality graphene in combination with successful optimization of the GFET technology, where extreme low source/drain contact resistances were obtained together with reduced parasitic pad capacitances. GFETs with gate lengths ranging from 0.5 µm to 2 µm have been characterized, and extrinsic f T and fmax frequencies of up to 34 GHz and 37 GHz, respectively, were obtained for GFETs with the shortest gate lengths. Simulations based on a small-signal equivalent circuit model are in good agreement with the measured data. Extrapolation predicts extrinsic f T and fmax values of approximately 100 GHz at Lg=50 nm. Further optimization of the GFET technology enables fmax values above 100 GHz, which is suitable for many millimeter wave applications.

Wide bandwidth terahertz mixers based on graphene FETs

“…As it can be seen from Fig. 3, the CE can be as high as -21 dB assuming 2 times lower contact resistance, which is possible to achieve using our recently developed technology [7].…”

“…The THz mixers based on the GFETs were fabricated on Si substrate using the high-quality CVD graphene [7]. An optical micrograph of the mixer chip is shown in Fig.…”

The Dependence of the High-Frequency Performance of Graphene Field-Effect Transistors on Channel Transport Properties

“…However, the high-frequency performance of state-of-the-art graphene field-effect transistors (GFETs) is significantly reduced. The highest published extrinsic (measured) transit frequency (f T ) and maximum frequency of oscillation (f max ) of GFETs are typically below 100 GHz [4]. For comparison, the high electron-mobility transistors (HEMTs) based on III-V compounds, with lowfield mobilities above 10 4 cm 2 /Vs, reveal a f T and f max up to 1 THz at deep-sub-µm gate lengths [5].…”

“…An approach has been proposed to realize the drain-current saturation in GFETs without a bandgap formation but via velocity saturation of charge carriers at high fields [7]. This approach has recently been applied in the development of GFETs with a state-of-the-art high-frequency performance operating in the velocity saturation mode [4], [8]. Nevertheless, there is a need to improve material quality and fabrication processes to minimize the extrinsic factors to fully exploit graphene for high-frequency applications.…”

“…A relatively thick oxide layer allows for the reduction of parasitic-pad capacitances. In stage (i), the transferred graphene film is covered with a 5 nm thick Al 2 O 3 layer [4], as indicated by the 1 st dielectric layer in Fig. 2.…”