This study reports AlGaN/GaN high-electron-mobility transistors (HEMTs) fabricated by the Stepper Lithography on a 4-inch wafer for Ka-Band applications. Small gate length (LG) of 100 nm was achieved through a 2-Step Photolithography Process and the gate region of the AlGaN/GaN HEMT was defined by using two lithography steps to form gamma-shaped gates. The 4-inch AlGaN/GaN HEMT wafer demonstrated high electrical performance uniformity with respect to the maximum drain-source current density (IDSS), the peak extrinsic output transconductance (Gm), and the threshold voltage (Vth). At ${\mathrm{ V}}_{\mathrm{ DS}}\,\,=$ 20 V, the AlGaN/GaN HEMT exhibits an ${\mathrm{ I}}_{\mathrm{ DSS}}$ of 1004.2 mA/mm, a Gm value of 363.6 mS/mm, a maximum output power density (POUT(MAX)) of over 10 W/mm, and a power gain of 8.8 dB with a maximum 51.1% Power-added efficiency (PAE) at 28 GHz in Continuous Wave (CW) mode. The results show the potential of AlGaN/GaN HEMT fabrication with high yield and outstanding RF performance using Stepper Lithography for 5G applications.

Herein, the AlGaN/GaN high-electron-mobility transistors (HEMTs) on silicon substrates using thick copper-metallized interconnects with Pt diffusion barrier layer for Ka-band application are reported. High output power density of 6.6Wmm(-1) with power-added efficiency (PAE) of 45.6% at 28 GHz is achieved for the 4 x 50 mu m device in continuous-wave (CW) mode. No obvious change in the drain-source current (I-DS) is observed for the device under 40 V high-voltage stress for 100 h and the device shows good thermal stability when annealed at 300 degrees C for 30 min. It demonstrates that the AlGaN/GaN HEMTs on silicon substrate with thick copper-metallized interconnects can enhance the device performance with good reliability for future 5 G applications.

In this paper, AlGaN/GaN high-electron-mobility transistors (HEMTs) with ohmic etching patterns (OEPs) “fabricated to improve device radio frequency (RF) performance for Ka-band applications” are reported. The fabricated AlGaN/GaN HEMTs with OEP structures were used to reduce the source and drain resistances (Rs and Rd) for RF performance improvements. Within the proposed study using 1 μm hole, 3 μm hole, 1 μm line, and 3 μm line OEP HEMTs with 2 × 25 μm gate widths, the small signal performance, large signal performance, and minimum noise figure (NFmin) with optimized values were measured for 1 μm line OEP HEMTs. The cut-off frequency (fT) and maximum oscillation frequency (fmax) value of the 1 μm line OEP device exhibited optimized values of 36.4 GHz and 158.29 GHz, respectively. The load–pull results show that the 1 μm line OEP HEMTs exhibited an optimized maximum output power density (Pout, max) of 1.94 W/mm at 28 GHz. The 1 μm line OEP HEMTs also exhibited an optimized NFmin of 1.75 dB at 28 GHz. The increase in the contact area between the ohmic metal and the AlGaN barrier layer was used to reduce the contact resistance of the OEP HEMTs, and the results show that the 1 μm line OEP HEMT could be fabricated, producing the best improvement in RF performance for Ka-band applications.

In this paper, AlGaN/GaN high electron mobility transistors (HEMTs) with etched-fin gate structures fabricated to improve device linearity for Ka-band application are reported. Within the proposed study of planar, one-etched-fin, four-etched-fin, and nine-etched-fin devices, which have 50-μm, 25-μm, 10-μm, and 5-μm partial gate widths, respectively, the four-etched-fin gate AlGaN/GaN HEMT devices have demonstrated optimized device linearity with respect to the extrinsic transconductance (Gm) value, the output third order intercept point (OIP3), and the third-order intermodulation output power (IMD3) level. The IMD3 is improved by 7 dB at 30 GHz for the 4 × 50 μm HEMT device. The OIP3 is found to reach a maximum value of 36.43 dBm with the four-etched-fin device, which exhibits high potential for the advancement of wireless power amplifier components for Ka band applications.

The effect of different SiNx thicknesses on the performance of AlGaN/GaN high-electron-mobility transistors (HEMTs) was investigated in this paper. The current, transconductance (Gm), cut-off frequency (fT), maximum oscillation frequency (fmax), power performance, and output third-order intercept point (OIP3) of devices with three different SiNx thicknesses (150 nm, 200 nm, and 250 nm) were measured and analyzed. The DC measurements revealed an increase in both the drain-source current (IDS) and Gm values of the device with increasing SiNx thickness. The S-parameter measurement results show that devices with a higher SiNx thickness exhibit improved fT and fmax. Regarding power performance, thicker SiNx devices also improve the output power density (Pout) and power-added efficiency (PAE) in the Ka-band. In addition, the two-tone measurement results at 28 GHz show that the OIP3 increased from 35.60 dBm to 40.87 dBm as the SiNx thickness increased from 150 nm to 250 nm. The device’s characteristics improved by appropriately increasing the SiNx thickness.

A GaN metal-insulator-semiconductor high electronmobility transistor (MIS-HEMT) using tri-gate architecture and hybrid ferroelectric charge trap gate stack is demonstrated for normally-off operation. Compared with the conventional planar device, the tri-gate device has the 2-D electron gas (2-DEG) channel exposed on the nanowire sidewalls, so that the trapped charges in the HfON charge-trapping layer can easily deplete the channel from the sidewalls, leading to a high positive threshold voltage (V-th) to realize the normally-off operation. Moreover, through this electrostatic control on the sidewall, a high density of negative charge caused by hybrid ferroelectric charge trap gate stack with the optimized tri-gate structure, the tri-gate device can achieve normally-off GaN device with both low on-resistance (R-ON) and high positive V-th. The designed tri-gate device exhibits a high V-th of +2.61 V at current density (I-DS) = 1 mu A/mm, a high maximum current density (I-DS, MAX) of 896 mA/mm, a low R-ON of 5.0 Omega center dot mm and a high breakdown voltage (BV) of 788 V. To the best of our knowledge, the proposed tri-gate device shows the lowest specific on-resistance (R-ON,R- SP) among reported normallyoff GaN device results with BV > 650 V.

GaN HEMT is an ideal device for power switching applications. However, owing to the false turn-on issue and the requirements for fail-safe operation for the device to be used for electrical vehicles application, a high threshold voltage normally-off GaN HEMT is desired. One of the methods to realize the normally-off operation is to use a charge storage layer under the gate region. However, the magnitude of threshold voltage shift is limited by the charge storage capability of the gate dielectric layer.