Enhancement of $f_{\mathrm {max}}$ to 910 GHz by Adopting Asymmetric Gate Recess and Double-Side-Doped Structure in 75-nm-Gate InAlAs/InGaAs HEMTs

Abstract

A high maximum frequency of oscillation (f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> ) of 910 GHz was achieved at InAlAs/InGaAs highelectron mobility transistors (HEMTs) with a relatively long gate length (L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G</sub> ) of 75 nm by adopting an asymmetric gate recess and a double-side-doped structure. The f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> improved significantly by extending the drain-side gate recess length (L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RD</sub> ) to 250 nm; meanwhile, the source-side gate-recess length (L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RS</sub> ) was kept to 70 nm. The improvement in fmax was due to a decrease in the drain output conductance (g <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</sub> ) and drain-to-gate capacitance (CGD) after the extension of L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RD</sub> . gd was further suppressedby applying a double-side-doped structure to the InP-based HEMTs. A reduction in g <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</sub> resulted in a drastic improvement in f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> even though L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G</sub> was a longer value.