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

We have successfully developed 30-nm enhancement-mode (E-mode) InGaAs/InAlAs high electron mobility transistors (HEMTs) with an extremely high transconductance (g_m ) of 2.22 S/mm, a current gain cutoff frequency (f_T) of 554 GHz, and a maximum oscillation frequency (f_max ) 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_m independent of the gate length (L_g ) and a greatly reduced output conductance (g_d).