Epitaxial graphene RF field-effect transistors

Abstract

In this paper, the recent development of graphene FETs on a wafer scale, including DC and RF performance is presented. The epitaxial growth of graphene is under development on two-inch wafers using both Si-sublimation of Si or C-face SiC(0001) substrates and graphene growth using MBE. The quality of graphene is characterized by Raman spectroscopy and TEM (transmission electron microscopy). The graphene RF FETs are fabricated with a high-k (Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ) gate dielectric layer and metal gate stack. Ambipolar behaviors are observed with a ptype FET at Vg <-10 V. The 2x12 ¿m graphene FETs with gate length (Lg) of 2 ¿m exhibit extrinsic f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> and f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> of 2.7 GHz and 3.4 GHz, respectively, at V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ds</sub> = 5 V. With an extrinsic gm improvement of 148 mS/mm at Vds = 9 V, the extrinsic f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> and f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> are 4.4 GHz and 6 GHz, respectively. With graphene FETs fabricated with reduced source-drain spacing of 1 ¿m, on-state current density, measured at Vgs = 5 V, improves dramatically to as high as 1.2 A/mm at Vds = 1 V and 3 A/mm at Vds = 5 V, respectively. The current drive level is the highest ever observed in any semiconductor FETs. The Ion/Ioff ratio is 3 to 4. The extrinsic f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> and f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> of 4.4 GHz and 12 GHz are measured, respectively, at Vds = 5 V, making the intrinsic ft*Lg = 10 GHz*¿m. This is comparable to that of Si NMOS. Graphene FETs with a shorter gate length is in progress and will be presented.