Showing papers by "Xiaohua Ma published in 2022"

General synthesis of ultrafine metal oxide/reduced graphene oxide nanocomposites for ultrahigh-flux nanofiltration membrane

Abstract: Abstract Graphene-based membranes have great potential to revolutionize nanofiltration technology, but achieving high solute rejections at high water flux remains extremely challenging. Herein, a family of ultrafine metal oxide/reduced graphene oxide (rGO) nanocomposites are synthesized through a heterogenous nucleation and diffusion-controlled growth process for dye nanofiltration. The synthesis is based on the utilization of oxygen functional groups on GO surface as preferential active sites for heterogeneous nucleation, leading to the formation of sub-3 nm size, monodispersing as well as high-density loading of metal oxide nanoparticles. The anchored ultrafine nanoparticles could inhibit the wrinkling of the rGO nanosheet, forming highly stable colloidal solutions for the solution processing fabrication of nanofiltration membranes. By functioning as pillars, the nanoparticles remarkably increase both vertical interlayer spacing and lateral tortuous paths of the rGO membranes, offering a water permeability of 225 L m −2 h −1 bar −1 and selectivity up to 98% in the size-exclusion separation of methyl blue.

Ti3C2Tx MXene Nanoflakes Embedded with Copper Indium Selenide Nanoparticles for Desalination and Water Purification through High-Efficiency Solar-Driven Membrane Evaporation.

Abstract: Solar-driven interface evaporation recently emerges as one of the most promising methods for seawater desalination and wastewater purification, mainly due to its low energy consumption. However, there still exist special issues in the present material system based on conventional noble metals or two-dimensional (2D) nanomaterials etc., such as high costs, low light-to-heat conversion efficiencies, and unideal channels for water transport. Herein, a composite photothermal membrane based on Ti3C2Tx MXene nanoflakes/copper indium selenide (CIS) nanoparticles is reported for highly efficient solar-driven interface evaporation toward water treatment applications. Results indicate that the introduction of CIS improves the spatial accessibility of the membrane by increasing the interlayer spacings and wettability of MXene nanoflakes and enhances light absorption capability as well as reduces reflection for the photothermal membrane. Simultaneously, utilization of the MXene/CIS composite membrane improves the efficiency of light-to-heat conversion probably due to formation of a Schottky junction between MXene and CIS. The highest water evaporation rate of 1.434 kgm-2 h-1 and a maximum water evaporation efficiency of 90.04% as well as a considerable cost-effectiveness of 62.35 g h-1/$ are achieved by using the MXene/CIS composite membrane for solar interface evaporation, which also exhibits excellent durability and light intensity adaptability. In addition, the composite photothermal membrane shows excellent impurity removal ability, e.g., >98% for salt ions, >99.8% for heavy metal ions, and ∼100% for dyes molecules. This work paves a promising avenue for the practical application of MXene in the field of water treatment.

High RF Performance GaN-on-Si HEMTs With Passivation Implanted Termination

Abstract: This work reports recent progress in the sub-6 GHz power performance of GaN-based HEMTs grown on high resistivity silicon substrates with passivation implanted termination (PIT) process. Thanks to the mitigated electric field crowding at the gate edge and the suppressed negative fixed charge-induced carrier depletion, the fabricated HEMTs demonstrate a low leakage current, a high ON/OFF current ratio of 10⁸, and improved breakdown voltage associated with a current collapse at 40 V drain quiescent condition of as low as 5.6%. S-band continuous-wave large signal measurements yield a high power-added efficiency (PAE) of 69%, a drain efficiency (DE) of 72%, and an output power density ( ${P}_{\text{out}}$ ) of 7.2 W/mm at ${V}_{\text{DS}}=30$ V. Moreover, the transistor delivers a maximum ${P}_{\text{out}}$ up to 10.2 W/mm with a peak PAE of 63.8% at ${V}_{\text{DS}}=40$ V. The PAE and ${P}_{\text{out}}$ as a function of drain bias indicate that the transistors remain constant high PAE and linearly increased ${P}_{\text{out}}$ over a wide range of drain voltage variation. These excellent results have demonstrated the PIT process could be an attractive technique to facilitate the application of high-performance and cost-competitive GaN-on-Si HEMTs for 5G wireless base stations.

Silk Protein Based Volatile Threshold Switching Memristors for Neuromorphic Computing

Abstract: Memristors based neuromorphic devices can efficiently process complex information and fundamentally overcome the bottleneck of traditional computing based on von Neumann architecture. Meanwhile, natural biomaterials have attracted significant attention for biologically integrated electronic devices due to their excellent biocompatibility, mechanical flexibility, and controllable biodegradability. Thus, biomaterial‐based memristors may have a transformative impact on bridging electronic neuromorphic systems and biological systems. However, the working voltage in biological system is low, but the operation voltages of conventional memristors are high, violating the energy‐efficient biological system. Here, high‐performance silk fibroin‐based threshold switching (TS) memristors are demonstrated, which reveal an on‐current of 1 mA, a low threshold voltage (Vth) of 0.17 V, a high selectivity of 3 × 106, and a steep turn‐on slope of <2.5 mV dec–1. Meanwhile, the silk TS devices depict outstanding device uniformity and stability even at high humidity (80%) and temperature (70 °C) environments. The silk TS devices exhibit typical short‐term plasticity (STP) of biological synapses including pair‐pulse facilitation (PPF). More importantly, a leaky integrate‐and‐fire (LIF) artificial neuron is successfully realized based on the volatile characteristics of silk TS memristors. These achievements pave the way for utilizing silk biomaterials in advanced bioelectronics and neuromorphic computing.

High performance millimeter-wave InAlN/GaN HEMT for low voltage RF applications via regrown Ohmic contact with contact ledge structure

Abstract: Benefitting from regrown Ohmic contact with a contact ledge structure, high performance millimeter-wave InAlN/GaN HEMT is fabricated to satisfy low voltage RF applications. Different from the commonly seen fabrication process for regrown Ohmic contact, the scheme proposed in this work features MBE regrowth of n+ GaN on the whole wafer after formation of regrowth well without masks and partial removal of n+ GaN grown on the access region by self-stopping etching. The remaining n+ GaN on the barrier, serving as contact ledges, provides an additional current path to achieve the reduced equivalent source-drain distance and, thus, improved output current, and more current contribution is made by contact ledge as the actual source-drain distance shrinks. With the assistance of contact ledge, the fabricated device demonstrates output current density of 2.8 A/mm, a peak extrinsic transconductance of 823 mS/mm, a knee voltage of 1.6 V, and an on-resistance of 0.47 Ω·mm. Although self-stopping etching is performed on the access region, the device exhibits ignorable current collapse. At 30 GHz and VDS of 6 V, decent power-added-efficiency of 52% together with output power density of 1.2 W/mm is achieved, revealing the great potential of the proposed regrown Ohmic contact with contact ledge structure for low voltage RF applications.

Demonstration of β-Ga₂O₃ Superjunction-Equivalent MOSFETs

Abstract: In this work, we, for the first time, demonstrate $\beta $ -Ga₂O₃ lateral superjunction (SJ) -equivalent metal–oxide–semiconductor field-effect transistors (MOSFETs). The electric field engineering is implemented by the alternatively arranged p-NiO/n-Ga₂O₃ lateral hetero-SJ, which is constructed through the selective epitaxial filling of p-NiO pillars into the trenched drift region of $\beta $ -Ga₂O₃. The static electrical characteristics indicate that $\beta $ -Ga₂O₃ SJ-equivalent MOSFETs outperform the control transistor without the SJ structure. In particular, the Ga₂O₃SJ-equivalent MOSFET with a p-NiO pillar width of 2 $\mu \text{m}$ demonstrates a breakdown voltage ( ${V}_{\text {br}}$ ) of 1362 V and a power figure-of-merit (PFOM) of 39 MW/cm², which are 2.42 and 4.86 times higher, respectively, than those of the control device. The large divergence of the experimental performance from the theoretical predictions is attributed to the charge imbalance caused by the substrate-assisted depletion effect and superimposed interfacial charges. With the proper interface engineering and controlled doping, it is expected that utilizing p-NiO/n-Ga₂O₃ hetero-SJ is a promising technological strategy to allow a favorable trade-off between ${V}_{\text {br}}$ and ON-state loss of Ga₂O₃ transistors for the high-efficiency power conversion.

Improved Power Performance and the Mechanism of AlGaN/GaN HEMTs Using Si-Rich SiN/Si3N4 Bilayer Passivation

Abstract: AlGaN/GaN high-electron-mobility transistors (HEMTs) with Si-rich SiN/Si3N4 bilayer passivation were studied in this article. The use of a Si-rich SiN interlayer leads to improved channel transport property, current collapse, power performance, and temperature-dependent stability. Devices without Si-rich SiN interlayer passivation exhibit an increase in the gate leakage current by over three orders of magnitudes with temperature increasing from 300 to 420 K, leading to an increase in a current collapse from 9.7% to 24.7%, while the devices with Si-rich SiN passivation exhibit a weak temperature dependence of leakage current and a constant current collapse about 5%. Small signal characterization shows that Si-rich SiN passivation results in a remarkable decrease in the effective gate length by ~15% with temperature up to 420 K. At 17 GHz, devices with Si-rich SiN interlayer passivation exhibit an output power density of 7 W/mm and a peak power-added efficiency (PAE) of 56%. The improved power performance of devices using Si-rich SiN interlayer passivation is attributed to the suppressed current collapse and superior device stability under high channel temperature.

Hardware-algorithm collaborative computing with photonic spiking neuron chip based on integrated Fabry-Pérot laser with saturable absorber

Abstract: Photonic neuromorphic computing has emerged as a promising avenue toward building a low-latency and energy-efficient non-von-Neuman computing system. Photonic spiking neural network (PSNN) exploits brain-like spatiotemporal processing to realize high-performance neuromorphic computing. However, the nonlinear computation of PSNN remains a significant challenging. Here, we proposed and fabricated a photonic spiking neuron chip based on an integrated Fabry–Pérot laser with a saturable absorber (FP-SA) for the first time. The nonlinear neuron-like dynamics including temporal integration, threshold and spike generation, refractory period, and cascadability were experimentally demonstrated, which offers an indispensable fundamental building block to construct the PSNN hardware. Furthermore, we proposed time-multiplexed spike encoding to realize functional PSNN far beyond the hardware integration scale limit. PSNNs with single/cascaded photonic spiking neurons were experimentally demonstrated to realize hardware-algorithm collaborative computing, showing capability in performing classification tasks with supervised learning algorithm, which paves the way for multi-layer PSNN for solving complex tasks.

Bio-Inspired In-Sensor Compression and Computing Based on Phototransistors.

Abstract: The biological nervous system possesses a powerful information processing capability, and only needs a partial signal stimulation to perceive the entire signal. Likewise, the hardware implementation of an information processing system with similar capabilities is of great significance, for reducing the dimensions of data from sensors and improving the processing efficiency. Here, it is reported that indium-gallium-zinc-oxide thin film phototransistors exhibit the optoelectronic switching and light-tunable synaptic characteristics for in-sensor compression and computing. Phototransistor arrays can compress the signal while sensing, to realize in-sensor compression. Additionally, a reservoir computing network can also be implemented via phototransistors for in-sensor computing. By integrating these two systems, a neuromorphic system for high-efficiency in-sensor compression and computing is demonstrated. The results reveal that even for cases where the signal is compressed by 50%, the recognition accuracy of reconstructed signal still reaches ≈96%. The work paves the way for efficient information processing of human-computer interactions and the Internet of Things.

Physical Unclonable Functions Based on Transient Form of Memristors for Emergency Defenses

Abstract: In this letter, transient form of diffusive memristors with cross-point structure of W/Ag/MgO/Ag/W for physical unclonable functions (PUF) were proposed for the first time. The stochastic dispersion of Ag in MgO switching layer made the randomness maximized, which achieved an inter-chip Hamming distance of 49.1%. Importantly, triggered failure of the transient PUF devices was activated in deionized water at room temperature after 3 min immersion. Additionally, the transient PUF devices were transferred onto flexible polyimide substrate by water-assisted transfer printing method without any bits flipped, which achieved physical disappearance in deionized water finally. This transient form of memristor provides powerful insights into next-generation PUF design and hardware security for emergency defenses.

Demonstration of 16 THz V Johnson's figure-of-merit and 36 THz V fmax·VBK in ultrathin barrier AlGaN/GaN HEMTs with slant-field-plate T-gates

Abstract: In this work, ultrathin barrier (∼6 nm) AlGaN/GaN high-electron-mobility transistors (HEMTs) with in situ SiN gate dielectric and slant-field plate (SFP) T-gates were fabricated and analyzed. Since the proposed scheme of gate dielectric and SFP effectively suppresses the gate leakage and alleviates the peak electric field (E-field) around gate region, the maximum breakdown voltage ( VBK) was improved to 92 V, which is 54 V higher than that of the conventional device. The fabricated ultrathin AlGaN/GaN HEMT with 60-nm SFP-T-gate exhibited the peak fT of 177 GHz and peak fmax of 393 GHz, yielding high figure-of-merits of fT · VBK = 16 THz V and fmax·VBK = 36 THz V. Moreover, load-pull measurements at 30 GHz reveal that these devices deliver output power density ( Pout) of 4.6 W/mm at Vds = 20 V and high power-added efficiency up to 52.5% at Vds = 10 V. Essentially, the experimental results indicate that the employment of SFP and in situ SiN gate dielectric is an attractive approach to balance the breakdown and speed for millimeter wave devices.

Recessed-Gate Ga₂O₃-on-SiC MOSFETs Demonstrating a Stable Power Figure of Merit of 100 mW/cm² Up to 200 °C

Abstract: Recessed-gate $\beta $ -gallium oxide (Ga₂O₃) MOSFETs on the heterogeneous Ga₂O₃-on-SiC (GaOSiC) wafer are fabricated and characterized. The GaOSiC transistors with an ${L}_{\mathrm {SD}}$ of $11~{\mu } \text{m}$ exhibit the decent and stable electrical characteristics with the temperature varying from 25 °C to 200 °C, including a breakdown voltage ( ${V}_{\mathrm {br}}$ ) of 1000 V, a specific ON-resistance ( ${R}_{\mathrm{\scriptscriptstyle ON},\mathrm {sp}}$ ) of ~100 m ${\Omega }~\cdot $ cm², a drive current of 91 mA/mm, and a power figure of merit (P-FOM) of ~100 MW/cm². Characterization of the transfer length method (TLM) structure fabricated on the same heterogeneous wafer demonstrates that the reduced transfer length ( ${L}_{T}$ ) at the $\beta $ -Ga₂O₃/Ti/Au contact interface compensates for the increased sheet resistance ( ${R}_{\mathrm {SH}}$ ) of $\beta $ -Ga₂O₃ film at the elevated temperature, which leads to the stable electrical performance of the GaOSiC devices.

8.7 W/mm output power density and 42% power-added-efficiency at 30 GHz for AlGaN/GaN HEMTs using Si-rich SiN passivation interlayer

Abstract: In this work, high-performance millimeter-wave AlGaN/GaN structures for high-electron-mobility transistors (HEMTs) are presented using a Si-rich SiN passivation layer. The analysis of transient and x-ray photoelectron spectroscopy measurements revealed that the presence of the Si-rich SiN layer leads to a decrease in the deep-level surface traps by mitigating the formation of Ga–O bonds. This results in a suppressed current collapse from 11% to 5% as well as a decreased knee voltage (Vknee). The current gain cutoff frequency and the maximum oscillation frequency of the devices with the Si-rich SiN layer exhibit the values of 74 and 140 GHz, respectively. Moreover, load-pull measurements at 30 GHz show that the devices containing the Si-rich SiN deliver excellent output power density of 8.7 W/mm at Vds = 28 V and high power-added efficiency up to 48% at Vds = 10 V. The enhanced power performance of HEMTs using Si-rich SiN interlayer passivation is attributed to the reduced Vknee, the suppressed current collapse, and the improved drain current.

Dynamic evolution process from bipolar to complementary resistive switching in non-inert electrode RRAM

Abstract: At present, the physical mechanism of complementary resistive switching (CRS) devices remains controversial. In this Letter, stable CRS can be achieved in Pt/AlOxNy/Ta resistive random access memory (RRAM). A dynamic evolution from bipolar resistive switching to CRS can be evidently observed in non-inert electrodes RRAM. The causes of CRS behavior are analyzed in detail, and these phenomena are attributed to the different oxidation degrees of the top electrode and propose that the transition state can be used as a signal for the emergence of CRS behavior. Moreover, the model is partially supported by measured switching behavior of the Pt/AlOxNy/TaOx device. This research contributes to the understanding of the CRS behavior physical mechanism in non-inert electrodes RRAM devices.

Fully Physically Transient Volatile Memristor Based on Mg/Magnesium Oxide for Biodegradable Neuromorphic Electronics

Abstract: In this article, a fully physically transient volatile memristor utilizing Mg as an active electrode with a structure of W/MgO/Mg/W was proposed. The fully transient device exhibited remarkable threshold switching (TS) performance via Mg2+ cations migration dynamics and emulated the paired-pulse facilitation (PPF), paired-pulse depression (PPD), and transition from short-term to long-term plasticity of a biological synapse successfully. In addition, a water-assisted transfer printing (WTP) method was exploited to fabricate the fully physically transient system on biodegradable and biocompatible substrates. This study confirms that the fully transient volatile memristor owns outstanding value toward security neuromorphic computing, biodegradable, and bio-integrated electronic systems.

Influence of non-inert electrode thickness on the performance of complementary resistive switching in AlOxNy-based RRAM

Abstract: This Letter investigates the effect of non-inert electrode thickness on the performance of complementary resistive switching (CRS). Five devices with different Ta electrode thicknesses (0, 2, 5, 10, and 20-nm) are fabricated. For devices with 2, 5, and 10-nm electrode thicknesses, CRS behavior can be obtained through an evolution process, while devices with 0 and 20-nm Ta electrode thicknesses always maintain stable bipolar resistive switching behavior. By analyzing the evolution process and current conduction mechanisms, the influence of non-inert electrode thickness on the performance of CRS is studied, and different oxidation degrees of a non-inert electrode are used to explain the different resistive switching performance in these devices. Aside from that, the model is verified by applying an asymmetric voltage sweeping method. This paper further clarifies the physical mechanism of CRS behavior in non-inert electrode resistive random access memory and provides a way to optimize the performance of CRS behavior.

The DC Performance and RF Characteristics of GaN-Based HEMTs Improvement Using Graded AlGaN Back Barrier and Fe/C Co-Doped Buffer

Abstract: In this article, the impact of the graded AlGaN back barrier and Fe\C co-doping buffer structure on the AlGaN $/$ GaN high electron mobility transistors (HEMTs) is proposed and systematically investigated. Due to effective suppression of Fe tail in unintentionally doped GaN (uid-GaN) layer by the insertion of the thick graded AlGaN back barrier layer, a large maximum drain current density and a transconductance peak are achieved. Meanwhile, the breakdown voltage is significantly improved by the use of Fe\C co-doping GaN buffer design. More importantly, it is revealed that the graded-AlGaN design can reduce the range and intensity of the electrical potential distribution in uid-GaN layer and then effectively suppress the acceptor-induced trapping\detrapping effect under high drain voltage. The RF small-signal performance of Fe-doped GaN (GaN:Fe)\C co-doping buffer HEMT exhibits significant improvement. In addition, load-pull measurement at 8 GHz revealed that a saturation power increases from 38.04 to 41.07 dB, a power gain increases from 9.06 to 10.58 dB, and an associate power-added-efficiency (PAE) increased from 40.27% to 50.18%. Our proposed GaN-based epitaxial structure can not only suppress the gate lag by reduce AlGaN surface electric field, but it can also suppress the drain lag by reduce the amplitude and range of potential distribution. It indicates that our proposed device has great potential for future high-voltage RF power amplifier application.

Structural and thermal analysis of polycrystalline diamond thin film grown on GaN-on-SiC with an interlayer of 20 nm PECVD-SiN

Abstract: A 1.5- μm polycrystalline diamond was deposited on the AlGaN/GaN heterojunction on the SiC substrate with a 20-nm SiN dielectric. A 4.9% increase in 2DEG density after the diamond growth due to the increase in tensile strain of the GaN layer is confirmed by micro-Raman measurements. The interfacial analysis through the transmission electron microscopy and electron energy loss spectroscopy shows a thickness reduction in the SiN layer of ∼1.7 nm, which converts to a thin SiC layer at the diamond/SiN interface, and no carbon diffusion is found in the SiN layer after the diamond growth. Device simulation using the thermal properties extracted by time domain thermoreflectance predicts a temperature drop of 17.1 °C when the diamond only covers the device access region and reveals that the improvement of thermal boundary resistance is much more effective than that of the diamond thermal conductivity for the top-side heat spreading, which is mainly due to the limited thickness of the top diamond film.

Simulation Study of Lateral Schottky Barrier IMPATT Diode Based on AlGaN/GaN 2-DEG for Terahertz Applications

Abstract: In this article, a novel lateral Schottky barrier high-low impact-ionization-avalanche-transit-time (IMPATT) diode, i.e., the high-electron mobility transistor (HEMT)-like IMPATT (HIMPATT) diode, is proposed based on the AlGaN/GaN 2-D electron gas (2-DEG). Numerical simulation demonstrated that the HIMPATT diode shows better characteristics than the conventional vertical IMPATT diode because of a superior property of the AlGaN/GaN 2-DEG. Comparing with the vertical IMPATT diode, the optimum frequency of HIMPATT diode rises from 260 to 380 GHz, the maximum RF output power ${P}_{RF}$ rises from 2.30 to 3.06 MW/cm², and the maximum conversion efficiency $\eta $ rises from 14.7% to 18.5%. In addition, simulation results reveal that the trench length ${L}_{r}$ and depth ${D}_{r}$ of the 2-DEG channel significantly influence the output performances of HIMPATT diode, where the frequency characteristic is more sensitive to the trench length ${L}_{r}$ and the RF power characteristic is more sensitive to the trench depth ${D}_{r}$ . By designing the pattern shape of the trench area, a monolithic integrated HIMPATT diode oscillator array can be implemented on one chip to generate a wider frequency band with great RF performances than the vertical IMPATT diode. It provides more variable designing options for the applications of the HIMPATT diode in the terahertz regime.

Leakage current reduction in β-Ga2O3 Schottky barrier diode with p-NiOx guard ring

Abstract: A β-Ga2O3 Schottky barrier diode (SBD) with a p-type NiOx guard ring was fabricated, and the reverse leakage and subthreshold leakage current reduction was found at high temperatures from temperature-dependent I–V characteristics. The functional mechanisms of NiOx as edge termination on leakage reduction were studied. NiOx can increase the barrier height and passivate the defects at the interface, resulting in the suppression of subthreshold leakage and elimination of current crowding effect confirmed by a thermal emission microscope. From the temperature-dependent x-ray photoelectron spectroscopy characteristics, more holes generated to deplete Ga2O3 at higher temperatures were found. It leads to reduce the reverse leakage current. The small-polaron transportation in NiOx is proposed to argue the implausibility of the leakage conduction in NiOx. This work will offer critical physical insight and a valuable route for developing low-leakage Ga2O3 SBDs.

Improved electrical performance of lateral β-Ga2O3 MOSFETs utilizing slanted fin channel structure

Abstract: In this Letter, lateral slanted-fin-channel β-Ga2O3 metal-oxide-semiconductor field effect transistors (MOSFETs) are demonstrated. A 600-nm thick n-type doped channel layer is adopted to improve output characteristics. The tri-gate structure enhances gate control in the proposed β-Ga2O3 MOSFETs, showing an on/off ratio as high as 109. In particular, the slanted-fin-channel structure, mainly located in the gate region, reduces the peak electric field in the Ga2O3 channel due to the gradual regulation of a threshold voltage. The slanted-fin-channel β-Ga2O3 MOSFETs show a breakdown voltage ( Vbr) of 2400 V and a power figure-of-merit of 193 MW/cm2, which are almost 2 and 5.5 times larger, respectively, than those of conventional straight-fin-channel devices. These results imply that the slanted-fin channel structure provides a viable way of fabricating high-performance β-Ga2O3 MOSFET power devices.

High-Performance AlGaN/GaN HEMTs With Hybrid Schottky–Ohmic Drain for Ka-Band Applications

Abstract: A hybrid Schottky–ohmic drain technology for millimeter-wave (mmW) AlGaN/GaN high-electron-mobility transistors (HEMTs) is proposed. The Schottky metal extension in the ohmic region of drain reduces the actual source–drain spacing, resulting in a smaller ON-resistance and a higher maximum current. Extended Schottky metal in the drain region modulates the electric-field distribution, thereby leading to an improved breakdown voltage, suppressed current collapse, and high reliability. Compared with the ohmic drain, the current gain cutoff frequency ( ${f}_{T}$ ) was improved from 64 to 76 GHz, and the maximum oscillation frequency ( ${f}_{\text {max}}$ ) was improved from 125 to 157 GHz, resulting from the decreased parasitic drain resistance ( ${R}_{d}$ ). Moreover, large-signal measurements in continuous wave (CW) at 30 GHz demonstrated a peak power-added efficiency (PAE) of 45.5% and a saturated output power density ( ${P}_{\text {sat}}$ ) of 8.5 W/mm at ${V}_{\text {ds}}= {30}$ V. In addition, the direct current (DC) and radio frequency (RF) characteristics showed a negligible degradation after large-signal measurements at 30 GHz.