New insulated-gate inverted structure AlGaAs/GaAs/n-AlGaAs HEMT ring oscillator

Inverted-structure high electron mobility transistors with insulated-gate structure, i.e. AlGaAs/GaAs/n-AlGaAs, have been successfully applied to E/D-type DCFL ring oscillators. High transconductance of 280 mS/mm was obtained at 77 K in an enhancement-mode FET with 0.8 ¿m gate length. Gate leakage current was small enough even at a gate voltage of +1.4 V both at 300 K and 77 K, and a high logic swing of more than 1 V was achieved using a DCFL inverter. A 21-stage ring oscillator showed a minimum gate delay as small as 18.0 ps with power dissipation of 520 ¿W/gate at 77 K.