Low-Voltage and High-Speed Operations of 30-nm-Gate Pseudomorphic $\hbox{In}_{0.52}\hbox{Al}_{0.48}\hbox{As}/\hbox{In}_{0.7}\hbox{Ga}_{0.3} \hbox{As}$ HEMTs Under Cryogenic Conditions

In this letter, we fabricated 30-nm-gate pseudomorphic In
_0.52
Al
_0.48
As/In
_0.7
Ga
_0.3
As HEMTs with multilayer cap structures to reduce source and drain parasitic resistances; we measured their dc and radio-frequency characteristics at 300, 77, and 16 K under various bias conditions. The maximum cutoff frequency fT was 498 GHz at 300 K and 577 GHz at 77 K. The maximum fT exceeded 600 GHz at 16 K. Even at a drain-source voltage
V

_ds
of 0.4 V, we obtained an
fT
of 500 GHz at 16 K. This indicates that cryogenic HEMTs are favorable for low-voltage and high-speed operations. Furthermore, the present 30-nm-gate HEMTs at 300 K show almost the same fT values at the same dc-power dissipation as compared to 85-nm-gate InSb-channel HEMTs. The improvement of the maximum-oscillation-frequency
f

_max
values was also observed at 77 and 16 K.