Ti/Au/Al/Ni/Au low contact resistance and sharp edge acuity for highly scalable AlGaN/GaN HEMTs

Abstract

In this letter, we have reported a novel metal scheme Ti/Au/Al/Ni/Au for ohmic contact on AlGaN/GaN high-electron-mobility transistors. The reported metal scheme is observed to show minimum metal out-diffusion and sharp edge acuity at high-temperature annealing, which facilitates aggressive scaling of source-drain separation (LSD). We have demonstrated LSD as low as 300 nm with gate length (L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> ) of 100 nm for this metal stack. We observed improvement in on-resistance (Ron) from 3 to 1.25 Q·mm, transconductance (gm) from 276 to 365 mS/mm, saturation drain current (I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DS,sat</sub> ) from 906 to 1230 mA/mm, and unity current gain frequency (f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> ) from 70 to 93 GHz by scaling LSD from 3 μm to 300 nm. The gate lengths for all devices were 100 nm.