  Scaling of GaN high-electron-mobility transistors (HEMTs) usually increases
gate leakage current and deteriorates breakdown characteristic, limiting the
maximum drain current and output power density. These bottlenecks can be
circumvented by inserting a dielectric material under the gate of HEMTs. Doped
HfO2 is an excellent dielectric material but unexplored so far as the gate
material of HEMTs for high-speed device application. Here we demonstrate that
Zr-doped HfO2 (HZO)-gated InAlN/GaN metal-insulator-semiconductor (MIS) HEMTs
exhibit remarkable properties. The device with a gate length (Lg) of 50 nm
exhibits maximum drain current (Id,max) of 2.15 A/mm, a transconductance (gm)
peak of 476 mS/mm, an on/off current ratio (Ion/Ioff) of 9.3*107, a low
drain-induced barrier lowing (DIBL) of 45 mV/V. RF characterizations reveal a
current gain cutoff frequency (fT) of 155 GHz and a maximum oscillation
frequency (fmax) of 250 GHz, resulting in a (fT*fmax)1/2 of 197 GHz.These
properties, particularly the high (fT/fmax)1/2 and JFOM are highly desirable
for the millimeter-wave power applications, demonstrating the great
technological potential of HZO/InAlN/GaN MIS-HEMTs.
