Top-gated graphene field-effect transistors on SiC substrates

Abstract

We report on a demonstration of top-gated graphene field-effect transistors (FETs) fabricated on epitaxial SiC substrate. Composite stacks, benzocyclobutene and atomic layer deposition Al 2 O 3 , are used as the gate dielectrics to maintain intrinsic carrier mobility of graphene. All graphene FETs exhibit n-type transistor characteristics and the drain current is nearly linear dependence on gate and drain voltages. Despite a low field-effect mobility of 40 cm 2 /(V s), a maximum cutoff frequency of 4.6 GHz and a maximum oscillation frequency of 1.5 GHz were obtained for the graphene devices with a gate length of 1 μm. Graphene, consisting of one or a few carbon atomic layers packed into a two dimensional (2D) hexagonal lattice, has attracted enormous attention over the last few years [1]. Graphene exhibits impressive transport properties, including high carrier mobility and saturation velocity [2]. As a result, it is a good candidate for radio-frequency (RF) field-effect transistor (FET) applications. So far, high quality graphene device with a maximum cutoff frequency (f T ) of 300 GHz has been obtained on thin exfoliated films of graphite [3].Although an excellent method to obtain single devices for scientific research, exfoliation is impractical for large-scale manufacturing of graphene sheets. However, mass production can be solved by epitaxial growth on SiC or metalcatalyzed chemical vapor deposition (CVD) [4,5]. To date, graphene FETs with f T beyond 100 GHz have also been achieved using graphene films synthesized by both methods [6,7]. Graphene by epitaxy on SiC is directly obtained on semi-insulating SiC substrates, so that no transfer is required before processing devices, as compared with the CVD method. Recently, graphene integrated circuits have been realized on SiC wafers [8], showing potential in practical applications. Nevertheless, the graphene on SiC substrates is still cost ineffective and not compatible with Si technologies.In this work, we present DC and RF performance of graphene FETs developed on SiC substrates. The graphene transistors are fabricated by the conventional top-down approach, holding the potential of compatibility with other semiconductor materials. An organic polymer film is introduced between graphene and regular gate dielectrics to minimize mobility degradation in top-gated graphene FETs. The output characteristics are nearly linear without clear current saturation before device breakdown. With a gate length of 1 μm and a low field-effect mobility of 40 cm 2 /(V s), a maximum cutoff frequency of 4.6 GHz and a maximum oscillation frequency (f MAX ) of 1.5 GHz were measured.The graphene was epitaxially grown on SiC. From the intensity ratio of the G peak to SiC substrate peaks and the shape of the 2D peak in the measured Raman spectrum of the graphene [9,10], it can be determined that most of the surface was covered by monolayer graphene, and only in few regions associated with pits bilayers started forming;

Hydroxyl-free buffered dielectric for graphene field-effect transistors

“…Actually, radio frequency (RF) FET devices on graphene grown both by CVD and on SiC have been fabricated and exhibit desirable high-frequency characteristics with the application of the BCB-buffered dielectric (Fig. S7) [49][50][51][52]. For example, a 300 nm topgate length FET device prepared on graphene grown on Cu by CVD operates with a cutoff frequency (f T ) of 11 GHz before de-embedding (Fig.…”

Raman Spectroscopy Imaging of Exceptional Electronic Properties in Epitaxial Graphene Grown on SiC

“…Therefore, large number of studies try to modify graphene layer properties in order to induce the opening of a gap. Some of the more common approaches to achieve this include formation of graphene ribbons [ 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 ], coexistence of various graphene layer numbers in single system [ 54 ], reshaping of graphene layer into bubbles and domes [ 16 ]. Epitaxial graphene is also frequently used in radio-frequency (RF)-transistors and amplifiers devices.…”