BN / Graphene / BN RF Transistors

In this work we demonstrate the first BN/graphene/BN transistor for high frequency RF applications. This sandwich structure allows a significant improvement in the mobility of graphene, which reaches more than 18,000 cm$^{2}$/Vs at room temperature. Graphene field effect transistors (GFETs) have been fabricated with L$_{DS}$= 800 nm and L$_{G}$=300 nm. The minimum conduction point of these devices is very close to zero, a result of the negligible substrate doping to the graphene. A current density in excess of 1 A/mm and DC transconductance above 200 mS/mm are achieved for both electron and hole conductions. RF characterization is performed for the first time on this device structure and initial results show a current-gain cut-off frequency $f_{T}$=10 GHz. These experimental results have been combined with simulations of the small-signal model to study the scaling potential of these GFETs for high frequency applications. The impact of the access resistances (R$_{s}$, R$_{d})$, the capacitances (C$_{gs}$, C$_{gd}$, C$_{ds})$, and the transconductance (g$_{m}$) on the frequency performance of the GFETs has also been studied. Finally, the fabricated devices have been compared to GFETs fabricated with SiO$_{2}$ substrate and Al$_{2}$O$_{3}$ gate dielectrics. The improved performance obtained by the BN/graphene/BN structure is very promising to enable the next generation of high frequency RF electronics.