Extremely High gm> 2.2 S/mm and fT> 550 GHz in 30-nm Enhancement-Mode InP-HEMTs with Pt/Mo/Ti/Pt/Au Buried Gate

Abstract

We have successfully developed 30-nm enhancement-mode (E-mode) InGaAs/InAlAs high electron mobility transistors (HEMTs) with an extremely high transconductance (g <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</sub> ) of 2.22 S/mm, a current gain cutoff frequency (f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> ) of 554 GHz, and 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 358 GHz. The excellent high-speed performance was obtained by using a Pt/Mo/ Ti/Pt/Au buried gate technology, which enabled E-mode operation for very short 30-nm HEMTs while maintaining a low access resistance as well as a low gate leakage current. The effectively short gate-to-channel distance suppressed the short channel effect, resulting in a very high g <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</sub> independent of the gate length (L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> ) and a greatly reduced output conductance (g <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</sub> ).