High-performance short-channel MESFETs with WSiN gate suppressing As-outdiffusion (SAINT-GEN.II)

The formation of a highly conductive channel, which is one of the most effective methods to achieve high-performance GaAs MESFETs, requires that As-outdiffusion during high-temperature annealing be suppressed, because As vacancy creates more implanted Si acceptors, decreasing channel conductance. A refractory metal, WSiN, that effectively suppressing As-outdiffusion has been applied in an n⁺ -self-aligned ion-implantation MESFET technology (SAINT-GEN.II), and the performance of the fabricated FETs experimentally evaluated. The device structure studied had a 10-keV implanted shallow channel with a buried p-layer and an Au-coated WSiN gate. A 630 mS/mm maximum transconductance at gate voltage of 0.6 V and 510 mS/V-mm K-value at threshold voltage of -0.14 V were obtained. A 920 mS/mm intrinsic transconductance was estimated from source resistance of 0.51 Ω-mm. The gate resistance was as small as 3 μΩ-cm. A cutoff frequency as high as 96 GHz was obtained by extrapolating the current gain of 0.5 to 25.5 GHz at the correct 6 dB/octave. The effective saturation velocity is estimated at 1.8×10⁷ cm/s. This represents an 80% improvement of velocity overshoot compared to long-gate MESFETs. The characteristics of a 23-stage ring oscillator using direct-coupled FET logic (DCFL) circuits with a propagation delay time of 6.7 ps/gate have also been investigated