Chemical Vapour Deposition Graphene Radio-Frequency Field-Effect Transistors

Abstract

We report the dc and rf performance of graphene rf field-effect transistors, where the graphene films are grown on copper by using the chemical vapour deposition (CVD) method and transferred to SiO2/Si substrates. Composite materials, benzocyclobutene and atomic layer deposition Al2O3 are used as the gate dielectrics. The observation of n-and p-type transitions verifies the ambipolar characteristics in the graphene layers. While the intrinsic carrier mobility of CVD graphene is extracted to be 1200 cm 2 /V•s, the parasitic series resistances are demonstrated to have a serious impact on device performance. With a gate length of 1 µm and an extrinsic transconductance of 72 mS/mm, a cutoff frequency of 6.6 GHz and a maximum oscillation frequency of 8.8 GHz are measured for the transistors, illustrating the potential of the CVD graphene for rf applications.

Top-gated graphene field-effect transistors on SiC substrates

“…The drain current I D , measured as a function of gate voltage V G , as shown in Figure 3, exhibits dominant n-type characteristics, differing from the ambipolar characteristics typically observed in exfoliated and CVD graphene [11]. For all of our graphene FETs, the Dirac point (the current minimum) always occurs at V G <6 V. The device transconductance g m , defined by dI D /dV G , is nearly constant over a wide V G range in the on-state (right axis in Figure 3).…”

“…With a reasonable value of C G =1.83×10 3 F/m 2 [11], the low-field μ FE is estimated to be ~40 cm 2 /(V s) at V D =0.1 V. One should notice that mobility extracted by this method is inevitably underestimated, because the influences of contact resistance are not excluded [7,11]. The contact resistance plays a dominant role in graphene devices and has an exponentially detrimental impact on the transconductance [12].…”

“…The gate dielectric film consists of first 10 nm of an organic seed layer made of benzocyclobutene, followed by an 8 nm film of Al 2 O 3 deposited by atomic layer deposition (ALD). Details of the fabrication processes are presented in [11]. Finally, the gate electrodes consisting of Ti/Au metals (10 nm/50 nm) are formed by optical lithography and liftoff.…”

“…The composite stacks have been proven to meet the requirements on gate dielectric [11]. Briefly, the gate dielectric layers are deposited on graphene prepared by mechanical exfoliation on SiO 2 /Si substrates.…”

“…The maximum frequency f MAX [11] defined as the frequency at which the power gain is equal to one, is measured to be 1.5 GHz for the graphene FET with f T =4.6 GHz. It is noted that f MAX , unlike f T , is highly dependent on the device layout and interconnects, including the metal thickness that affects the gate and source/drain resistance.…”