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Tri-gate GaN Junction High-Electron-Mobility Transistors

Diagrfam of tri- gate
Fig. 1. (top) Diagram of tri-gate junction HEMT, the fins can be seen in gate region, wrapped by NiO and gate metal. (bottom) SEM image of fin before and after NiO coating.
The tri-gate technology allows GaN HEMTs to realize enhancement-mode operation, superior gate control, and low leakage current. This work presents a GaN tri- gate transistor concept, the tri-gate GaN junction high- electron-mobility transistor (JHEMT), which comprises p-n junctions wrapping the AlGaN/GaN fins in the gate region. This tri-gate JHEMT differs from all the existing GaN FinFETs or tri-gate HEMTs, as they use the metal-insulator-semiconductor (MIS) gate stack. The p-n junction can offer stronger depletion than the MIS owing to a larger built-in potential (Vbi ) and the obviation of voltage drop in the insulating dielectrics, thereby making it easier to realize the E-mode and prevent the punch-through.
A self-aligned process is used to deposit the NiO and gate metal in the same lithography step. The NiO is deposited in a magnetron sputtering system using the NiO target. Fig.1 shows the scanning electron microscopy (SEM) images of the GaN fins before and after NiO sputtering, verifying the conformal NiO coverage. A hole concentration and mobility of 5×1019 cm-3 and 0.7 cm2/V3, respectively, are extracted for the sputtered p-NiO. For the tri-gate MISHEMTs.
Fig. 2(a) shows the double-sweep transfer characteristics (VDS = 5 V, saturation region) of the tri-gate JHEMTs and MISHEMTs with 60 nm WFin. The tri-gate JHEMT has a VTH of 0.45 V (extracted at 1 μA/mm drain current) and
a hysteresis below 0.1 V, while the tri-gate MISHEMTs show a negative VTH and ~0.6 V hysteresis. The close- to-60 mV/decade SS and small hysteresis in tri-gate JHEMTs suggest very small interface states in NiO-based junction gate. The tri-gate JHEMT faces larger gate leakage current when NiO/2DEG diode turns on. Fig. 2(b) shows the output characteristics of the 60-nm tri-gate JHEMTs and 40-nm tri-gate MISHEMTs with a similar VTH . The higher current density in the tri-gate JHEMT is mainly due to the larger portion of the gate for current conduction.
Fig. 2. Transfer and output characteristics of tri-gate JHEMT and MISHEMT. (a) compares transfer of junction

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