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In this paper, a high-efficiency compact power amplifier is designed and fabricated with a 0.25 μm GaN high electron mobility transistor (HEMT) to meet the demands of a high integration level and high efficiency for microwave wireless power transfer (WPT) systems. The proposed power amplifier (PA) is implemented using an internally matched method to achieve a compact circuit size. The output second and third harmonic impedances can be optimized through output matching circuits, eliminating the need for additional harmonic matching networks. This approach simplifies the design of matching circuits and reduces the circuit size. Furthermore, the input third harmonic has been controled for improving the efficiency of DC-to-RF conversion. The total size of the proposed PA is 13.4   ×   13.5 mm2. The test results obtained from the continuous wave (CW) testing indicate that the output power of the power amplifier at 2.45 GHz reaches 43.75 dBm. Additionally, the large-signal gain is measured at 15.75 dB, and the power-added efficiency (PAE) achieves a value of 78.5%. [ABSTRACT FROM AUTHOR]

The extraction of small‐signal parameters is of great importance for the modeling of InP heterojunction bipolar transistors (HBTs). This letter proposes an improved small‐signal parameter extraction method that considers both the emitter–collector capacitance effect and the current crowding effect. The corresponding parameter extraction procedure based on closed‐form equations is outlined. Furthermore, the model parameter extraction method is validated using two different‐sized InP HBT devices with multibias S‐parameters. The results demonstrate that the established small‐signal model exhibits greater than 90% accuracy across the frequency range of 1–110 GHz. In particular, in the high‐frequency band (above 50 GHz), the proposed model exhibits an improvement in accuracy of 7.4% after considering the emitter–collector capacitance and current crowding effects. This method can contribute to accurate modeling of the noise and large‐signal performance of InP HBT. [ABSTRACT FROM AUTHOR]

In this paper, a GaN high-electron-mobility transistor (HEMT) compact high-power wide-band power amplifier with an operation frequency from 0.8 GHz to 2 GHz is proposed. In order to realize a compact design, an internally matched method is employed. A wide-band matching strategy with an LC network and a multi-stage wide-band power combiner/divider is introduced in this design to achieve a wide bandwidth. A power combination structure is applied to have high output power. Wire-spiral inductance and film capacitors are employed to construct the compact matching network. The equivalent inductance of the bonding wire is also involved in the matching network. Experimental results show that the PAE (power-added efficiency) during the whole operation's bandwidth (0.8 GHz to 2.0 GHz) is from 40% to 57%. The output power can reach from 48.3 dBm to 49.8 dBm with a circuit size of 30.8 × 27.4 mm 2 . [ABSTRACT FROM AUTHOR]

The compact model plays a pivotal role as a critical link between device fabrication and circuit design. While conventional compact model theories and techniques are generally mature, the intricate physical mechanisms of gallium nitride (GaN) high‐electron mobility transistors (HEMTs) pose challenges due to their strong non‐linearity in high‐power radio frequency (RF) applications. This complexity hinders achieving the required precision for applications using traditional modeling methods. Therefore, the development of physics‐based compact modeling techniques becomes crucial for a deeper understanding of the intricate features of GaN HEMTs. This paper explores the advancements and the current state‐of‐the‐art in physics‐based compact models. The comprehensive review covers both intrinsic core models and real‐device effects models. Core models are presented with a focus on fundamental concepts, development overviews, and applications. Additionally, the real‐device effects models are introduced, encompassing advanced characterization techniques and modeling methodologies. Furthermore, the paper outlines future trends in physics‐based compact modeling, providing valuable insights for individuals engaged in transistor compact modeling work. [ABSTRACT FROM AUTHOR]

This study presents a novel approach for optimizing the parameters of monolithic microwave integrated circuit (MMIC) functional units using machine‐learning techniques and multi‐objective optimization algorithms. We utilize advanced machine‐learning methods, including random forest, artificial neural networks (ANNs), and recurrent neural networks (RNNs), to construct highly accurate models that predict the performance of these units. These models are subsequently integrated with a multi‐objective optimization algorithm, specifically the multi‐objective particle swarm optimization (MOPSO), to generate inverse design solutions for both the geometric designs of the units and the fabrication parameters of the heterogeneous integration process. Our approach, which has been validated through chip fabrication and testing, has demonstrated its robustness as a tool for achieving optimal MMIC designs. It not only reduces the design time but also enhances the manufacturability of MMICs, thereby opening new avenues in microwave and RF circuit design. [ABSTRACT FROM AUTHOR]

A 2–26.5GHz broadband amplifier monolithic microwave integrated circuit (MMIC) based on the 0.15 μm GaN high electron mobility transistor process has been developed. The broadband amplifier adopts a two‐stage distributed amplifier cascade structure, which improves the gain of the broadband amplifier. Further, the capacitive coupling is used to improve the gain bandwidth product of the power amplifier. To improve the output return loss of the wideband amplifier, a tuning stub is introduced at the output of the circuit. The on‐wafer measurement results show that the amplifier has a gain greater than 18 dB, gain flatness less than ±1.4 dB, and saturated output power >35 dBm with a >13% power added efficiency in the whole band. [ABSTRACT FROM AUTHOR]

Summary: In order to ensure that the electromagnetic compatibility and mutual interference of multiple radar network systems meet the requirements, a 55‐W gallium nitride (GaN) high harmonics suppression (HSs) high power amplifier (HPA) microwave monolithic integrated circuit (MMIC) with an operating frequency of 5.1–6.3 GHz is designed for radar network system. An HSs method using self‐resonant capacitor integrated in the output matching network of HPA is proposed to improve the HSs characteristics. The measured results show that under the condition of 100‐μs pulse width and 10% duty cycle, the HSs are greater than 48 dBc while the output power is greater than 55 W, the power gain is 21 dB, and the power additional efficiency (PAE) is 54%, which is suitable for use in radar network system. The size of the HPA is 3.55 × 4.05 mm2. [ABSTRACT FROM AUTHOR]

A novel large signal compact modeling for GaN HEMT has been proposed in this paper, and the harmonic mean is used to simulate the I‐V curves, combining the saturation and the linear region. The traditional compact modelings has two typical forms, the empirical modeling and the physical modeling. The empirical modeling is accurate and fast, but lacking the physical meaning. On the contrary, the physical modeling derived from the physical equation, is more complex, with the low speed and the poor convergence. This novel modeling inherently has both advantages, the fast speed, and so forth, and the physical meaning. The saturation region covers the most states of the power amplifiers, and Chih‐Tang Sah equation with clear physical meanings is adopted in this region. In linear region, on the contrary, the current varies more steeply with the voltage, and thus the empirical formula is used. [ABSTRACT FROM AUTHOR]

In order to meet the application requirements of radar networks for high efficiency and high second harmonic suppression (SHS) of power amplifiers, this paper proposes a C-band 30 W power amplifier (PA) microwave monolithic integrated circuit (MMIC) based on 0.25 μm gallium nitride (GaN) high electron mobility transistor (HEMT) process. The proposed PA uses a two-stage amplifier structure to achieve high power gain. A topology with SHS is designed in the output-matching network. Besides, the large signal model load pull simulation and the harmonic control technology in the output stage are used to improve efficiency. The high-power additional efficiency (PAE) and high SHS of the PA MMIC are achieved simultaneously. In the 5–6 GHz frequency range, multiple indicator measurements of the proposed PA show that output power is over 45 dBm, the PAE is more than 57%, the SHS exceeds 45 dBc, the power gain is greater than 24 dB, which are conducted under the condition of 100 μs pulse width and 10% duty cycle. In addition, the size of the PA MMIC, including bonding pads, is 3.3 × 3.1 mm2. [ABSTRACT FROM AUTHOR]

A novel method to fabricate the oxidized silicon-terminated (C–Si–O) diamond metal-oxide-semi- conductor field-effect transistors (MOSFETs) by replacing the retained SiO2 masks with an atomic layer deposition (ALD)-Al2O3 film as the main gate insulator was proposed for the first time. Compositional analysis across the SiO2 masks and on the air-exposed C–Si–O (111) diamond surface has been carried out by utilizing secondary ion mass spectroscopy (SIMS) and Auger electron spectroscopy (AES) techniques, respectively. Furthermore, we revealed that, under selectively epitaxial growth of diamond through a SiO2 mask, a carbon-rich film was formed on SiO2 and C–Si bonding was realized at the SiO2/(111) diamond interface. The fabricated device with a source and drain distance (${L}_{SD}$) of $3 \,\mu \text{m}$ exhibits a distinct threshold voltage (${V}_{TH}$) of −5.6 V and a maximum drain current density (${I}_{D\_{}{MAX}}$) up to −311 mA/mm, which is a record value among normally-off single-crystalline diamond MOSFETs to date. In the case of having ALD-Al2O3 as the main gate insulator, normally-off operation of the C–Si–O diamond MOSFETs has a stark contrast with the typically normally-on performance of the hydrogen-terminated (C–H) diamond MOSFETs, which is mainly due to the smaller negative electron affinity of C–Si–O diamond compared with that of C–H diamond. These results indicate that the proposed C–Si–O (111) diamond MOSFETs with excellent normally-off operation and large drain current density are promising to fulfill the requirements of fail-safe and current drive capabilities in power device applications. [ABSTRACT FROM AUTHOR]

We propose a novel method for extracting the electromagnetic parameters (complex permittivity and permeability) of magnetic thin-film materials. The method extracts electromagnetic parameters of the magnetic thin films from effective electromagnetic parameters by using the supported vector machine (SVM). We validated the method in the frequency range of 1-8 GHz. The results show that the errors for both [epsilon]' and [mu]' are less than 0.5%, and the errors of both tan [[delta].sub.[epsilon]] and tan [[delta].sub.[mu]] are less than 0.001. Index Terms--Complex permeability, complex permittivity, microwave measurement, support vector machine (SVM).

In this paper, a potentiometric method is used for monitoring the concentration of glutamine in the bioprocess by employing silicon nanowire biosensors. Just one hydrolyzation reaction was used, which is much more convenient compared with the two-stage reactions in the published papers. For the silicon nanowire biosensor, the Al2O3 sensing layer provides a highly sensitive to solution-pH, which has near-Nernstian sensitivity. The sensitive region to detect glutamine is from ≤40 μM to 20 mM. The Sigmoidal function was used to model the pH-signal variation versus the glutamine concentration. Compared with the amperometric methods, a consistent result from different devices could be directly obtained. It is a fast and direct method achieved with our real-time setup. Also, it is a label-free method because just the pH variation of the solution is monitored. The obtained results show the feasibility of the potentiometric method for monitoring the glutamine concentrations in fermentation processes. Our approach in this paper can be applied to various analytes. [ABSTRACT FROM AUTHOR]

In this article, the normally- OFF oxidized Si-terminated (C–Si) diamond metal–oxide–semiconductor field-effect transistors (MOSFETs) with as-deposited 0.5-nm silicon on diamond annealed at high temperature as the subsurface p-channel were presented for the first time. A novel method utilizing both a metal mask to realize the regrown heavily boron-doped (001) diamond layer first (p+-diamond-first) and a molecular beam deposition (MBD) method to procure atomic-scale silicon deposition was achieved. Scanning transmission electron microscopy (STEM) and energy-dispersive X-ray spectroscopy (EDS) element mapping results suggest that the C–Si diamond/Al2O3 interface is quite continuous and atomically flat. A remarkably high threshold voltage (${V}_{\text{TH}}$) of −10 V and a maximum drain current density (${I}_{D\_{}{\text{MAX}}}$) of −156 mA/mm are simultaneously achieved in the fabricated devices. The devices with different source and drain (S/D) distances ($L_{\text{SD}}$) deliver robust ${V}_{\text{TH}}$ results and feature low OFF-state S/D leakage current $\vert {I}_{\text{leakage}}\vert $ of ~ $6\times10$ −6 mA/mm at ${V}_{\text{GS}}$ = 0 V. The extracted field-effect mobility is as high as 127 cm2 $\cdot \text{V}$ −1 $\cdot \text{s}$ −1 and the interface state density is as low as $4.35\times10$ 12 eV−1 $\cdot $ cm−2. These competitive results reveal that this first attempt of employing the combination of p+-diamond-first and MBD approaches promotes the integration of the advanced silicon manufacturing process with wide bandgap diamond material for power applications. [ABSTRACT FROM AUTHOR]

The polar rapid transfer alignment (RTA) is preferred to initialize the moving base. The heading error under the grid frame accumulates with time, and the aid to navigation is required to calibrate the strapdown inertial navigation system (SINS). However, the Arctic has a complex environment where auxiliary navigation devices, customarily used in low and medium latitudes, cannot operate appropriately in polar regions. The SINS attitude reference may contain errors to contaminate the measurement quality of RTA, causing alignment failure. Thus,we introducedpolarized-light navigation to offer the heading and assist attitude matching. However, its heading error is associated with the longitude error amplifiedwith increasing latitudes, and the outputs from systems are not unified into an identical navigation frame. For success in initialization at high latitudes, this work innovatively proposed a polar rapid transfer alignment assisted by the improved polarized-light navigation. Firstly, the grid heading of the polarized-light navigation was redefined under the grid frame, and the proposed weighted-clustering algorithm was used to process the skylight polarization pattern and extract the angle out. Eventually, we established the mathematical model of RTA with disturbances and augmented the grid heading solution from the polarized-light navigation into measurements, solving the low-quality attitude reference of the master SINS. Simulations and semiphysical experiments demonstrated that the proposed algorithm performed better, and the estimate error approached only several minutes of arc when the master attitude reference had over 1-degree attitude error. [ABSTRACT FROM AUTHOR]

Compact model of flexible radio frequency (RF) electronic devices is crucial for flexible circuit designs. In this article, a compact model, including external strain effects for flexible RF gallium nitride (GaN) high-electron-mobility transistor, is presented. First, the carrier density and threshold voltage with external mechanical uniaxial strain is analytically characterized by introducing the strained piezoelectric charge $\Delta \sigma $ , Schottky barrier height $\Delta \phi _{B}$ , and surface state density $D_{\mathrm {it}}$ into the model. Then, the variations of the conduction band offset at the AlGaN/AlN and AlN/GaN interfaces are considered. Finally, the complete large-signal model is established after embedding strain effect into intrinsic drain current and nonlinear capacitance models. The proposed model is verified by measurements, including direct current $I$ – $V$ characteristics, small-signal $S$ -parameters up to 40 GHz, and large-signal power performance—output power, efficiency, and gain. The proposed model will be useful for the RF application of flexible electronics. [ABSTRACT FROM AUTHOR]

Mechanisms of trap effects are crucial to improving diamond-based transistor electrical performance. Here, the trap effects in hydrogen-terminated diamond metal–oxide–semiconductor field-effect transistors (HD MOSFETs) are investigated by separating the effects of gate dielectric bulk alumina (BA) and diamond substrate (DS) for the first time. First, the location of traps and their impact on the dynamic drain current are characterized by pulsed ${I}$ – ${V}$ characterization. The dynamic drain current is degraded by traps in both BA and DS. Furthermore, the quiescent-bias-point-dependent trapping effects are studied by different quiescent bias points to reveal the response intensity of these two kinds of traps. Second, to further respectively characterize the effects of traps in the BA and the DS on HD MOSFETs, the threshold voltage (${V}_{\text {th}}$) instability was characterized under negative gate bias stress (NGBS) conditions. Strong gate biases ranging from −4 to −8 V are selected to activate traps in DS. An extraordinary nonmonotonic change in ${V}_{\text {th}}$ is found under the −8 V NGBS condition. Moreover, the corresponding variation in ${V}_{\text {th}}$ is, unexpectedly, smaller than −4 and −6 V NGBS conditions. These phenomena indicate that the detrapping effect in the DS become dominant with increasing stress duration in the variation in ${V}_{\text {th}}$ under an NGBS of −8 V. Finally, based on these results, an improved kinetic model is proposed to separately describe the effects of traps in the BA and the DS. These results are useful for improving the performance of HD MOSFETs. [ABSTRACT FROM AUTHOR]

A reactive matching (RM) power amplifier (PA) can achieve higher efficiency than a distributed amplifier (DA). In this paper, RM PAs that cover 18–40 GHz are proposed by using one‐order and two‐order synthesised transformer networks (STNs) with GaN on Si technology. In this band, the PAs can provide ≥30 dBm and ≥31.9 dBm output power, with power‐added efficiency (PAE) of ≥17% and ≥15% in the continuous mode, respectively. Further, STNs are analysed using the transmission poles method (TPM) instead of the resonant frequency method (RFM). Thus, the limitations of output power and bandwidth are comprehensively derived. In the one‐order STN, the impedance transformation ratio (T1N) has a maximum value (TMAX_1N), limiting the output power. A two‐order STN is proposed, and the impedance transformation ratio maximum (TMAX_2N) can be improved to (TMAX_1N)2. The result of this paper will be helpful for wideband high‐power amplifier applications. [ABSTRACT FROM AUTHOR]

This article presents the design and performance of a terahertz on-chip coupled-grounded coplanar waveguide (GCPW) power combiner using a 50ÎĽm-thick InP process. The proposed topology uses two coupled-GCPW lines at the end of the input port to substitute two quarter-wavelength GCPW lines,which is different from the conventional Wilkinson power combiner and canavailably minimize the coverage area. According to the results obtained, forthe frequency range of 210â€"250z, the insertion losses for each two-waycombiner and four-way combiner were lower than 1.05 dB and 1.35 dB,respectively, and the in-band return losses were better than 11 dB. Moreover,the proposed on-chip GCPW-based combiners achieved a compromise in low-loss, broadband, and small-size, which can find wide applications in terahertz bands, such as power amplifiers and signal distribution networks. [ABSTRACT FROM AUTHOR]

Process fluctuations can significantly affect the yield of millimeter-wave circuits based on submicrometer semiconductor processes. A yield-improvement design that incorporates passive circuits is well established. However, how to consider the process fluctuation in active circuit designs (e.g., power amplifiers) and improve yield is still a challenge. In this article, a yield-improvement load—pull design method, which can be used to find optimum load impedance accounting for high yield while maintaining good output performance, is presented. The yield-improvement load—pull theory is described using an analytical model of transistor large-signal performance considering the process fluctuation. A method of the yield-improvement load—pull for the practical microwave monolithic integrated circuit (MMIC) design is introduced in detail. For demonstration purposes, a high-performance Ka-band power amplifier MMIC is designed. The results show that with the proposed yield-improvement load—pull method, an obvious improvement of yield can be observed with only minimal sacrifice of the output power (Pout) and the power added efficiency (ηPAE), respectively. As a result, the method of this article can be used to improve the yield of millimeter-wave/terahertz integrated circuits (ICs). [ABSTRACT FROM AUTHOR]

In this article, we report a study on the dc and RF linearity performances of a hydrogen-terminated (C-H) diamond field-effect transistor. An atomic-layer-deposited Al2O3 (ALD-Al2O3) based C-H diamond (100) MOSFET was fabricated and then characterized by dc- $I-V$ , $C-V$ , small-signal, large-signal, pulsed $I-V$ , and two-tone inter-modulation characteristics. The typical transfer results suggest that the presented device achieves a maximum transconductance $(g_{m-\max}) \times$ gate-voltage swing (GVS) product of 673.2 $\text{V}\cdot $ mS/mm, which is a record value among single-crystal diamond FETs to the best of our knowledge. The improved ${g}_{m}$ -linearity in this work can be attributed to the enhanced mobility performance, and the extracted effective mobility ($\mu _{{\mathrm {eff}}}$) varies from 105 to 200 cm2/ $\text{V}\cdot \text{s}$. Furthermore, theoretical calculations reveal that the obtained high-performance $\mu _{{\mathrm {eff}}}$ is mainly due to the low-density surface charged impurities (${ \approx } 3.7\times 10^{12}$ cm−2) and the alleviated surface roughness scattering. Small-signal RF measurement shows that the drain current swing (DCS) of ${f}_{T}$ is as high as −434 mA/mm. Unexpectedly, the RF output power performance at 2.6 GHz suffers from the severe drain current compression under the RF input drive. The subsequent pulsed ${I}$ – ${V}$ results reveal that the cause could be ascribed to the drain-lag trapping effect. Even so, the device still shows attractive IM3-to-Carrier ratio (-C/IM3) values in the linear region, which indicates that the diamond MOSFET is a prospective candidate for the RF linearity application. [ABSTRACT FROM AUTHOR]

A new scalable small‐signal model for 0.1 μm AlGaN/GaN HEMT up to 110 GHz is presented in this paper. The taps between the gate/drain manifold and fingers on the device has been investigated and included in the equivalent circuit. In addition, to ensure high scalability, a set of scaling rules are presented. A novel extraction procedure for extrinsic capacitances using full‐wave electromagnetic (FW‐EM) method has been introduced along with corresponding structures used for EM simulation. The nonlinear dependence of the extrinsic inductances on the gate‐width has been accounted for by a new scaling rule, which can be used to extract their value from measurement data. To guarantee the stability of the scaling coefficients, two devices with different gate‐width have been utilized for their generation. The proposed scalable model has been verified using 0.1 μm AlGaN/GaN HEMT devices with different gate‐widths and different gate‐fingers. The experiment results show good agreement between model and measurement S‐parameters up to 110 GHz. [ABSTRACT FROM AUTHOR]

In system‐level design, microwave amplifier needs to be cascaded with other components. In this scenario, the input and output of amplifier model have cascade capability to sense the variation of source and load impedance, and thus can accurately predict the forward and reverse propagating waves. In this letter, the principle and an extraction flow for a simplified polynomial behavioral model are introduced, and the cascade capability of the model is verified by experimental source‐pull and load‐pull results. By simulations, a subcircuit with a low noise amplifier and a power amplifier, which are cascaded, is used to establish behavioral models using the proposed method. It shows that the proposed model results have good agreement with circuits using both continuous wave and modulated signal excitation. Finally, by measurements, the cascaded results of two amplifiers models are compared with the overall results. The results of output waves and magnitude/phase up to third harmonics are consistent with each other. These results verify that the proposed behavioral model has the capability of cascade simulation. [ABSTRACT FROM AUTHOR]

In this paper, the full‐wave electromagnetic (FW‐EM) simulation approach for scalable small‐signal modeling of the GaN HEMT device is proposed. The scalable rules are deduced from the extracted parasitic parameters, which is according to a step‐by‐step parameter extraction method. Moreover, the accuracy is enhanced by considering the temperature‐dependent resistance (TDR) Rs and Rd, which are calculated by combining a universal thermal resistance model and the Rs and Rd under the pinch‐off condition. In the end, a set of GaN HEMT with a gate length of 0.25 μm is used for validation, and the experimental results show that good agreements have been achieved between the measured and the simulated scattering (S) parameters. [ABSTRACT FROM AUTHOR]

A scalable eletrothermal model is necessary for a high‐power amplifier design for accurate accounting of thermal effects. Toward this end, this study presents a scalable large‐signal model of gallium‐nitride (GaN) high‐electron‐mobility transistors (HEMTs) on diamond substrates. First, a three‐dimensional (3D) thermal analysis model was established. Then, a modified eletrothemal expression was proposed to predict thermal effects including scalability. For validation, the proposed model was implemented into quasi‐physics zone division (QPZD) large‐signal model. Results show that the proposed model accurately predicts the I–V curves of devices with different gate widths, gate fingers, and ambient temperatures. Moreover, the results of the model are consistent with on‐wafer measurements of 2 × 125, 4 × 125, and 10 × 50 μm of GaN‐on‐diamond HEMTs, indicating that the proposed model accurately predicts the DC–IV curves, scattering parameters, and large‐signal performance. The findings of this study can be useful for designing microwave diamond–GaN HEMT circuits. [ABSTRACT FROM AUTHOR]

In this paper, a new reconfigurable power divider (PD) is proposed to improve the efficiency of the three-way Doherty power amplifier (DPA). The conventional λ/4 transmission line is replaced by the proposed reconfigurable PD in the input of peaking amplifier, where the 90° phase shift and impedance matching can be achieved. Furthermore, the output power distribution ratio (PDR) can be continuously adjusted in a large range by adjusting the reverse voltage of the varactor diodes. Therefore, the reconfigurable PD with the best PDR can assign input power to the peaking amplifier. Experiment results show that the maximum measured power added efficiency (PAE) of the proposed three-way DPA is 49%, which is improved by 5% compared with conventional three-way DPA. [ABSTRACT FROM AUTHOR]

A reliable small‐signal modelling approach has been developed and applied on GaN‐on‐diamond high electron mobility transistor. The extrinsic elements' extraction procedure was improved to provide an accurate characterization for the quasistatic behaviour of the intrinsic transistor. The frequency independence of the intrinsic elements at active multibias condition has been considered as another objective in addition to measurements' fitting. Physical relevant values for the model elements have been obtained. The model accuracy was also validated by means of S‐parameters simulation, which showed a very good fitting of the measured data. [ABSTRACT FROM AUTHOR]

Flexible radio frequency (RF) devices are in high demand for wearable electronics; however, they currently do not offer sufficient output power for application in fifth-generation wireless communication systems. This paper reports a bendable gallium nitride (GaN) high-electron-mobility-transistor (HEMT) with state-of-the-art output power in the microwave band. In this study, a fabrication method is proposed, where HEMT is originally grown on silicon carbide (SiC) substrates. After thinning the SiC substrates down to 5 μm, HEMT is transferred using a copper film rather than flexible substrates used in other studies. The measurements indicated that the fabricated devices exhibited a saturation output power of 2.65 W, corresponding to a power density of 2.65 W/mm, which was associated with maximum power added efficiency (PAE) of 51% at 3 GHz. The performance of the fabricated device remained stable even with a bending radius of up to 0.6 cm. These results indicated that the proposed fabrication method can potentially be used to realize high-power flexible RF electronics. [ABSTRACT FROM AUTHOR]

In this article, a novel waveguide-to-microstrip transition with a built-in dc/IF return path is proposed, in which a traditional E- plane probe is directly connected to the backshort by a thin metal wire along the axis of the waveguide. The proposed waveguide-to-microstrip transition implements an additional dc/IF return path while realizing mode conversion. Moreover, the presence of the dc/IF return path has little influence on the performance of the original E- plane probe. The operating principle is analyzed by theoretical analysis and full-wave simulation, and the design procedure of the transition is also presented. To implement the proposed dc/IF return path on different substrates, two approaches, including direct integration with planar circuits or with wire bonding technology, are developed. Furthermore, two back-to-back transition prototypes working in the millimeter and submillimeter bands were designed and characterized. The measured results are in excellent agreement with the simulations. Finally, as an application example, a 70-/140-GHz unbalanced frequency doubler adopting this structure for both dc biasing and dc grounding was designed and fabricated. Measured results show that the conversion loss of the fabricated doubler is less than 13 dB in the range from 125 to 145 GHz, and the minimum conversion loss is 11 dB at 140 GHz with 100-mW input power. [ABSTRACT FROM AUTHOR]

This paper provides an overview of the developments in microwave diamond field‐effect transistor (D‐FET) technologies. Due to the ultrawide‐bandgap and high carrier velocity and thermal conductivity of diamond, it is a potential candidate for microwave power devices with high output power and operating frequency. Here, the properties of semiconductor materials for microwave applications are described. Then, the mechanisms of various diamond FETs are detailed. In recent years, hydrogen‐terminated diamond metal‐oxide‐semiconductor field‐effect transistors (HD MOSFETs) have been widely studied for their potential use in microwave power devices. Therefore, the structures and developments of HD MOSFETs are mainly discussed. Finally, in the prospective application of the HD FET microwave circuit, the state‐of‐the‐art large‐signal modeling of HD MOSFETs is presented. [ABSTRACT FROM AUTHOR]

Threshold voltage analysis can help reveal the reliability of semiconductor transistors and its underlying mechanism. Herein, negative constant voltage stress (NCVS)-induced threshold voltage instability is studied in hydrogen-terminated diamond metal-oxide-semiconductor field-effect transistors (HD MOSFETs) with an Al2O3 dielectric layer deposited via atomic layer deposition at 90 °C. An unusual bidirectional shift in threshold voltage (Vth) can be observed with time. When a weak gate NCVS is applied, Vth gradually decreases during the first 500 s but increases in the next 500 s. A similar but opposite phenomenon is observed when the HD MOSFETs are in a recovery stage upon removing the NCVS, i.e., Vth increases in the first 500 s but decreases in the next 4500 s. A kinetic hydrogen motion model shows that this phenomenon can be attributed to the larger characteristic time constant of the unactuated oxygen-dangling bonds (UODBs) compared to that of the traps in the gate dielectric. Consequently, the trapping effect dominates and decreases Vth at the onset of NCVS. After 500 s, the UODB effects can be observed, increasing Vth. In the recovery stage, Vth is larger than the initial value. Further, modified hydrogen kinetic equations accounting for the dynamic effects of UODBs and traps are provided to quantitatively analyze the results. [ABSTRACT FROM AUTHOR]

This paper presents the temperature dependence of small signal performance of GaN‐on‐diamond high electron mobility transistors (HEMTs) at an ambient temperature range from 0°C to 125°C. The temperature influence on the parasitic resistances together with the intrinsic parameters is investigated, and the temperature coefficients of these parameters are extracted from measured data. For comparison, a GaN‐on‐SiC device is also investigated. These results are important for the development and application of the GaN‐on‐diamond HEMT technology. [ABSTRACT FROM AUTHOR]

The harmonic power amplifiers (PAs) have potential to be used in the millimeter‐wave band, but the sophisticate parasitic network effects on the projection of reflection coefficient coverage from transistor package (TP) plane to current generator (CG) plane is an important challenge. In this work, every typical parasitic element with unique effect is derived theoretically. Thus, in the millimeter‐wave band, the reduced and rotated projection of parasitic network between the two planes becomes clear. The fundamental frequency (20 GHz), second harmonics (40 GHz), and third harmonics (60 GHz) load‐pull simulations using the commercial standard nonlinear transistor modeling are simulated. The simulation and derivation are consistent and show that output power and efficiency become less sensitive to harmonic tuning due to the lossy parasitic network. This work will be helpful for harmonic tuned transistor and PA design in the millimeter‐wave band, in the future. [ABSTRACT FROM AUTHOR]

An accurate analytical electrothermal drain current (Ids) model for AlGaN/GaN HEMTs is presented in this letter. The model is implemented into our recently proposed quasi‐physical zone division (QPZD) model for demonstration purpose. Compared with the original QPZD model, its electrothermal characteristics are enhanced by involving more fundamental temperature dependent elements. In addition, these elements are derived analytically based on physical mechanisms instead of former pure empirical fitting method. Thus, the extracted parameter values are more close to intrinsic values. An in house 0.15‐μm GaN HEMT is used for validation. Compared with the measured data at a wide ambient temperature range (245‐390 K), this electrothermal model demonstrates good accuracy to predict the DC characteristics and RF performances of GaN HEMTs. [ABSTRACT FROM AUTHOR]