Low frequency transconductance and output resistance dispersion of epitaxial graphene nanoribbon-based field effect transistors

摘要

Graphene-based devices have recently attracted strong attention due to very promising features such as two-dimensional material properties and high carrier mobility [1]. Significant effort has been placed on studies of high frequency characteristics of graphene transistors [2, 3] and first low-frequency noise studies have been reported [4]. However the low-frequency transconductance and output resistance dispersion of graphene FETs are less understood. These play a major role in determining the device performance and are the subject of the studies reported in this paper. The channel or the ungated region of the device is usually responsible for such effects. The Graphene Nano Ribbon Field Effect Transistors (GNRFETs) reported here have been fabricated using an array of parallel graphene nano ribbons, described in [2]. The devices were dual gate FETs fabricated with coplanar access structure for RF characterization. Ni/Au (50/300 nm) was used for source and drain contacts and the GNR array was defined by e-beam lithography. To achieve accurate ribbon width control, hydrogen silsesquioxane (HSQ) was used as mask material. The excess of graphene surface was then etched by O2 RIE. After removing HSQ, the Al2O3 gate oxide was obtained by oxidation of a thin aluminium layer (about 2nm) in two steps leading to a final thickness of ∼ 5 nm. Finally, the top gate (Lg=150 nm) was realized using Ni/Au 50/300nm. The photograph of the final device is shown in Fig. 1.