High fmax × LG Product of AlGaN/GaN HEMTs on Silicon with Thick Rectangular Gate

Abstract

In this letter, we successfully demonstrated a AlGaN/GaN high-electron mobility transistor on silicon substrate with high product of maximum oscillation frequency (fmax) and gate length (LG) by reducing the gate resistance (Rg) using a thick, high aspect ratio rectangular gate (R-gate) structure with an LG of 265 nm and thickness of 315 nm which was fabricated using a thick polymethyl methacrylate lift-off process. The maximum drain current is over 1 A/mm, and the peak transconductance is 291 mS/mm. The values of cutoff frequency and fmax are 43.7 GHz and 126.5 GHz at a drain voltage (Vd) of 12 V, respectively. Rg is extracted through the small-signal model, and the value is given as 0.21-{Omega } -mm which is comparable to devices with the T-gate structure. This low Rg results in a high fmax and high text{f}{max }times {mathrm{ L}}{mathrm{ G}} product of 33.52 GHz- mu text{m} , comparable to previously reported GaN-on-Si transistors for both R-gate and T-gate structures.