In this paper, DC, transient, and RF performances among AlGaN/GaN HEMTs with a no field plate structure (basic), a conventional gate field plate structure (GFP), and a double floating field plate structure (2FFP) were studied by utilizing SILVACO ATLAS 2D device technology computer-aided design (TCAD). The peak electric fields under the gate in drain-side can be alleviated effectively in 2FFP devices, compared with basic and GFP devices, which promotes the breakdown voltage (BV) and suppresses the current collapse phenomenon. As a result, the ON-resistance increase caused by the current collapse phenomena is dramatically suppressed in 2FFP ~19.9% compared with GFP ~49.8% when a 1 ms duration pre-stress was applied with V_ds = 300 V in the OFF-state. Because of the discontinuous FP structure, more electric field peaks appear at the edge of the FFP stacks, which leads to a higher BV of ~454.4 V compared to the GFP ~394.3 V and the basic devices ~57.6 V. Moreover, the 2FFP structure performs lower a parasitic capacitance of C_gs = 1.03 pF and C_gd = 0.13 pF than those of the GFP structure (i.e., C_gs = 1.89 pF and C_gd = 0.18 pF). Lower parasitic capacitances lead to a much higher cut-off frequency (f_t) of 46 GHz and a maximum oscillation frequency (f_max) of 130 GHz than those of the GFP structure (i.e., f_t = 27 GHz and f_max = 93 GHz). These results illustrate the superiority of the 2FFP structure for RF GaN HEMT and open up enormous opportunities for integrated RF GaN devices.

In this work, we present the novel application of SiN_x stress-engineering techniques for the suppression of short-channel effects in AlGaN/GaN high-electron-mobility transistors (HEMTs), accompanied by a comprehensive analysis of the underlying mechanisms. The compressive stress SiN_x passivation significantly enhances the barrier height at the heterojunction beneath the gate, maintaining it above the quasi-Fermi level even as V_ds rises to 20 V. As a result, in GaN devices with a gate length of 160 nm, the devices with compressive stress SiN_x passivation exhibit significantly lower drain-induced barrier lowering (DIBL) factors of 2.25 mV/V, 2.56 mV/V, 4.71 mV/V, and 3.84 mV/V corresponding to drain bias voltages of 5 V, 10 V, 15 V, and 20 V, respectively. Furthermore, as V_ds increases, there is an insignificant degradation in transconductance, subthreshold swing, leakage current, or output conductance. In contrast, the devices with stress-free passivation show relatively higher DIBL factors (greater than 20 mV/V) and substantial degradation in pinch-off performance and output characteristics. These results demonstrate that the SiN_x stress-engineering technique is an attractive technique to facilitate high-performance and high-reliability GaN-based HEMTs for radio frequency (RF) electronics applications.

The piezoelectric thin film composed of single-crystal lithium niobate (LiNbO₃) exhibits a remarkably high electromechanical coupling coefficient and minimal intrinsic losses, making it an optimal material for fabricating bulk acoustic wave resonators. However, contemporary first-order antisymmetric (A1) Lamb mode resonators based on LiNbO₃ thin films face specific challenges, such as inadequate mechanical stability, limited power capacity, and the presence of multiple spurious modes, which restrict their applicability in a broader context. In this paper, we present an innovative design for A1 Lamb mode resonators that incorporates a support-pillar structure. Integration of support pillars enables the dissipation of spurious wave energy to the substrate, effectively mitigating unwanted spurious modes. Additionally, this novel approach involves anchoring the piezoelectric thin film to a supportive framework, consequently enhancing mechanical stability while simultaneously improving the heat dissipation capabilities of the core.

This paper studied an atomic layer etching (ALE) technique with a surface treatment function for InAlN/GaN heterostructures with AlN spacer layers. Various parameters were attempted, and 30 s O₂ + 15 W BCl₃ was chosen as the optimal recipe. The optimal ALE approach exhibited satisfactory etching results, with regard to the etch-stop effect, compared with other techniques. The atomic force microscopy (AFM) results showed an etching per cycle (EPC) value of 0.15 nm/cycle, with a 0.996 fit coefficient and root mean square (RMS) surface roughness of around 0.61 nm (0.71 nm for as-grown sample), which was the lowest in comparison with digital etching (0.69 nm), Cl₂/BCl₃ continuous etching (0.91 nm) and BCl₃ continuous etching (0.89 nm). X-ray photoelectron spectroscopy (XPS) and scanning transmission electron microscopy with energy dispersive X-ray spectroscopy measurements (STEM/EDS) verified the indium clustered phenomena at the bottom apex of V-pit defects in the epi structure of InAlN/GaN high electron mobility transistors (HEMTs) for the first time, in addition to the surface morphology optimization for the ALE under-etching technique used in this work. The resistor hall effect (Hall) and AFM measurements demonstrated that after 4 or 5 ALE cycles, the two-dimensional electron gas (2-DEG) density and RMS roughness were improved by 15% and 11.4%, respectively, while the sheet resistance (R_sh) was reduced by 6.7%, suggesting a good surface treatment function. These findings were important for realizing high-performance InAlN/GaN HEMTs.

In this work, the DC performance and RF characteristics of GaN-based high-electron-mobility transistors (HEMTs) using the SiN_x stress-engineered technique were systematically investigated. It was observed that a significant reduction in the peak electric field and an increase in the effective barrier thickness in the devices with compressive SiN_x passivation contributed to the suppression of Fowler–Nordheim (FN) tunneling. As a result, the gate leakage decreased by more than an order of magnitude, and the breakdown voltage (BV) increased from 44 V to 84 V. Moreover, benefiting from enhanced gate control capability, the devices with compressive stress SiN_x passivation showed improved peak transconductance from 315 mS/mm to 366 mS/mm, along with a higher cutoff frequency (f_t) and maximum oscillation frequency (f_max) of 21.15 GHz and 35.66 GHz, respectively. Due to its enhanced frequency performance and improved pinch-off characteristics, the power performance of the devices with compressive stress SiN_x passivation was markedly superior to that of the devices with stress-free SiN_x passivation. These results confirm the substantial potential of the SiN_x stress-engineered technique for high-frequency and high-output power applications, which are crucial for future communication systems.

In this work, AlGaN/GaN high-electron-mobility transistors (HEMTs) with a nanocrystalline diamond (NCD)/SiN_x trench dual-passivated (TDP) structure were promoted, which demonstrated superior performance with a higher saturation output current (I_dss) of 1.266 A/mm, a higher maximum transconductance (G_mmax) of 0.329 S/mm, and a lower resistance (R_on) of 2.64 Ω·mm. Thermal simulations revealed a peak junction temperature of 386.36 K for TDP devices under V_ds/V_gs = 30 V/0 V, representing 13.7% and 4.5% reductions versus SiN_x single-passivated (SP, 447.59 K) and dual-passivated (DP, 404.58 K) devices, respectively. The results suggested that compared to conventional SP and DP devices, TDP devices can effectively suppress the self-heating effect, thereby improving output characteristics while maintaining superior RF small-signal characteristics. Moreover, the results of numerical simulations indicated that the enhanced electrothermal performance of TDP devices was predominantly attributed to the mitigation of temperature-induced degradation in electron mobility and drift velocity, thereby preserving their high power and high frequency capabilities. These results highlighted the significant potential of TDP devices to improve the performance of GaN HEMTs in high-power and high-frequency applications.