Graphene RF transistors with buried bottom gate

Abstract

To improve process induced mobility degradation of graphene, radio frequency (RF) transistors with buried bottom gates have been fabricated and characterized. In this process, graphene is transferred to the top of finished gates and source/drains as almost the very last step of the entire fabrication process. A unit graphene transistor shows the on-current of 130 μA/μm the I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</sub> /I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</sub> ratio of 5.31, and the maximum transconductance of 6.85μS/μm at V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</sub> = 0.1 V. The graphene RF transistor with a channel length of 600 nm shows a maximum oscillation frequency (f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> ) of 13 GHz and a cut-off frequency (f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> ) of 2 GHz after de-embedding. The higher f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> than f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> is due to less source-drain resistance (R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DS</sub> ) made by a fully-covered channel region by the buried gate. Because of the higher f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> the proposed device structure can be a promising candidate for graphene RF transistors and RF amplifiers.