In this paper, the authors report on the development of aluminum gallium nitride/gallium nitride (AlGaN/GaN) high electron mobility transistors (HEMTs) with improved surge protection characteristics provided by a metal-semiconductor-metal two-dimensional electron gas (MSM-2DEG) varactor connected in series to the gate of each HEMT. Under an electrostatic discharge surge stress of 1100 V or less, HEMTs that incorporate this protection feature do not exhibit any changes because the surge stress is directly blocked by the MSM-2DEG varactor. In addition, flip-chip (FC) technology is also used to further improve the thermal performance and reliability of the HEMTs. The heat generated in the 2DEG channel of the HEMT flows directly through the interconnect metal to the submount, and hence, it improves thermal conduction. The results of experiments conducted show that the proposed FC HEMT with MSM-2DEG varactor has significantly improved surge protection characteristics.

A proposed gas discharge tube (GDT) including two electrodes and one hollow insulator ring with extra Zinc Oxide (ZnO) sputtered surface is studied. The insulating ring of a GDT has variable or non-linear resistance characteristics. In comparison to the conventional design, the proposed GDT can provide early triggering capability during fast IEMI introduced and results a smaller residual surge current.

-The performance of the AlGaN/GaN MSM-2DEG varactor with different dielectric films deposited by the E-beam deposition is investigated in detail. The capacitance swing and the capacitance ratio of the varactor without dielectric film as well as with, SiO 2 , Gd 2 O 3 , and Si 3 N 4 films, respectively, are determined by electrodes of varying areas. The maximum capacitance, the minimum capacitance and the capacitance ratios are proportional to the increasing of the electrode areas. The capacitance ratio determined by the maximum and the minimum capacitance is found to be 18.35 (with Si 3 N 4 dielectric film) and 149.51 (without dielectric film), respectively. The transition voltages of the fabricated varactors are almost the same for a bias voltage of about ±5 V and leakage current can be lower three orders of magnitude while the varactors with dielectric films. The tunability of the capacitance ratio makes the AlGaN/GaN MSM-2DEG varactor with a dielectric film highly useful in multirange applications of a surge free preamplier.