GaN HEMT for High-performance Applications: A Revolutionary Technology

With the increased power density of gallium nitride (GaN) high electron mobility transistors (HEMTs), effective cooling is required to eliminate the self-heating effect. Incorporating diamond into GaN HEMT is an alternative way to dissipate the heat generated from the active region. In this review, the four main approaches for the integration of diamond and GaN are briefly reviewed, including bonding the GaN wafer and diamond wafer together, depositing diamond as a heat-dissipation layer on the GaN epitaxial layer or HEMTs, and the epitaxial growth of GaN on the diamond substrate. Due to the large lattice mismatch and thermal mismatch, as well as the crystal structure differences between diamond and GaN, all above works face some problems and challenges. Moreover, the review is focused on the state-of-art of polycrystalline or nanocrystalline diamond (NCD) passivation layers on the topside of GaN HEMTs, including the nucleation and growth of the diamond on GaN HEMTs, structure and interface analysis, and thermal characterization, as well as electrical performance of GaN HEMTs after diamond film growth. Upon comparing three different nucleation methods of diamond on GaN, electrostatic seeding is the most commonly used pretreatment method to enhance the nucleation density. NCDs are usually grown at lower temperatures (600–800 °C) on GaN HEMTs, and the methods of “gate after growth” and selective area growth are emphasized. The influence of interface quality on the heat dissipation of capped diamond on GaN is analyzed. We consider that effectively reducing the thermal boundary resistance, improving the regional quality at the interface, and optimizing the stress–strain state are needed to improve the heat-spreading performance and stability of GaN HEMTs. NCD-capped GaN HEMTs exhibit more than a 20% lower operating temperature, and the current density is also improved, which shows good application potential. Furthermore, the existing problems and challenges have also been discussed. The nucleation and growth characteristics of diamond itself and the integration of diamond and GaN HEMT are discussed together, which can more completely explain the thermal diffusion effect of diamond for GaN HEMT and the corresponding technical problems.

본 논문은 GaN(Gallium Nitride) HEMT(High Electron Mobility Transistor) die를 이용하여 S-대역 내부 정합형 전력 증폭기 설계, 제작 그리고 실험 결과에 대해 기술하였다. S-대역 내부 정합형 전력 증폭기를 설계하기 위하여 고유전율을 가지는 기판과 알루미나 기판을 이용하여 입/출력단 정합 회로를 설계 및 제작하였다. 측정 결과로는 펄스 모드로 동작시켰을 때 3 GHz에서 55.4 dBm의 출력 전력, 78 % 드레인 효율 그리고 11 dB의 전력 이득을 얻었다. This paper presents the design, fabrication and measurement results of a S-band internally-matched power amplifier using Gallium Nitride High Electron Mobility Transistor(GaN HEMT) die. In order to fabricate the S-band internally-matched power amplifier, a high dielectric substrate and alumina were used for input/output matching circuits. The measured output power is 55.4 dBm, the drain efficiency is 78 % and the power gain is 11 dB under pulse operation at the frequency of 3 GHz.

The development of high-quality gallium nitride (GaN) high electron mobility transistors (HEMTs) has provided opportunities for the next generation of high-performance radio frequency and power electronics. Operating devices with smaller length scales at higher voltages result in excessively high channel temperatures, which reduce performance and can have detrimental effects on the device's reliability. The thermal characterization of GaN HEMTs has traditionally been captured from either the top or bottom side of the device. Under this configuration, it has been possible to map the lateral temperature distribution across the device with optical methods such as infrared and Raman thermometry. Due to the presence of the gate metal, however, and often also the addition of a metal air bridge and/or field plate, the temperature of the GaN channel under the gate is typically inferred by numerical simulations. Furthermore, measuring the vertical temperature gradient across multiple epitaxial layers has shown to be challenging. This study proposes a new cross-sectional imaging technique to map the vertical temperature distribution in GaN HEMTs. Combining advanced cross-sectioning processing with the recently developed near bandgap transient thermoreflectance imaging technique, the full transient thermal distribution across a GaN HEMT is achieved. The cross-sectional thermal imaging of the GaN channel is used to study the effects of biasing on the Joule heating profile. Overall, the direct measurement of the GaN channel, capturing both the vertical and lateral gradient, will provide deeper insight into the device's degradation physics and supply further experimental data to validate previously developed electrothermal models.

Embedding is a technology which permits to build highly integrated, compact power sections. It also helps to minimise parasitic elements within the power sections, this way facilitating the use of novel, fast switching devices like gallium-nitride (GaN) high electron mobility transistors (HEMTs). This paper deals with required processes and the development of a power section with GaN HEMTs for a three phase drive inverter with a nominal power in the lower kW range; a version with discrete devices has also been built as a benchmark for the embedded solution.

AlGaN/GaN high-electron-mobility transistors (HEMTs) for applications in radiation environments has required the exact determination of their radiation hardness. Although bulk GaN is the preferred substrate for the epitaxial growth of GaN and AlGaN, (111) silicon is a possible substrate for HEMT devices. The stability of electrical parameters of enhancement-mode (E-mode) GaN HEMTs under gamma irradiation is an essential characterization for reliability. The present work reports the transfer characteristics degradation of E-mode GaN HEMTs under various total dose irradiation from 5krad up to 60Mrads. This represents the first comprehensive total dose study ranging from a few krads up the tens of Mrads. The measured device-to-device variations within groups of devices are presented. The evolutions of critical DC parameters with accumulated total dose is found to be significant at low doses and saturates at high dose levels. The degradation mechanism is very similar to the reported radiation-induced shallow electron traps that trap and release electrons in the near surface GaN and AlGaN layers. Due to the unique properties including high breakdown voltage, high electron mobility and high thermal stability, wide-bandgap semiconductor power electronic devices, especially Gallium Nitride (GaN) high-electron-mobility transistors (HEMTs), have shown great promise in space, defense and nuclear applications, which often involve radiation-hardened electronics that require high radiation tolerance to fluxes of neutrons or gamma ray of devices. To turn the promising potential of GaN HEMTs into reality, investigations on the influence of irradiation on the device performance and reliability are essential. Many studies have investigated the radiation hardness of group III–nitride compound semiconductor devices under various irradiation types, such as electrons, protons, neutrons, and X-rays and at various total irradiation doses. They generally showed higher radiation tolerance compared with Si because of high displacement energy of GaN, demonstrating the favorability of GaN devices in hard radiation environments. Many studies have investigated the influence of 60Co gamma radiation on the device electrical characteristics. However, they were all focusing on depletion mode (D-mode) devices. Enhancement mode (E-mode) GaN-on-Si transistors have been commercially available for years. Their major advantages over D-mode devices are elimination of negative voltage supply and the enabling of direct-coupled FET logic (DCFL) for digital circuits. They also improve the efficiency of commercial DC-DC converters in various power levels and topologies. A previous work on gamma radiation of E-mode GaN-on-Si HEMTs only reported cumulative total doses of up to 1 Mrads (Si). The present work provides a complete coverage of low-to-high irradiation doses from 5krads up to 60Mrads (Si), for commercially available E-mode GaN HEMTs and the devices are characterized to gauge variations in the critical DC parameters. To the best of the author’s knowledge, the present work is the first to investigate the gamma radiation tolerance of E-mode GaN HEMTs covering such a wide range of total doses. This facilitates the observation of the complete degradation behavior of DC parameters in hard radiation applications of the E-mode GaN HEMTs. The devices were supplied in the form of 0.9mm square passivated die with round solder bumps for contacts. They have a rated continuous drain-to-source voltage VDS of 60V, and a rated continuous drain current ID of 1A. These GaN-on-Si devices were fabricated on Si wafers considering process compatibility and cost. An aluminum nitride (AlN) thin layer was grown on the Si wafer to be a seed layer for the AlGaN/GaN heterostructure. Subsequently, the AlGaN/GaN heterostructure was grown on the AlN layer, with a thin AlGaN layer grown above the highly resistive GaN serving as a strained interface between the GaN and AlGaN crystal layers, allowing the creation of a two-dimensional electron gas (2DEG) filled with abundant free electrons with ultra-high mobility. The gate electrode was processed subsequently forming a depletion region under the gate. As an E-mode transistor, the device is turned on by applying a positive bias to the gate. All the irradiations were conducted at room temperature by 60Co gamma-rays with a flux of 318.5Rads (Si)/s, at the dry-cell panoramic gamma irradiator in the University of Maryland Radiation Facilities. The entire irradiation procedure consists of two parts. The first part is higher-dose irradiation with total doses of up to 60Mrads based on two stages. At the first stage, the devices were irradiated at 10Mrads, while at the second stage, the devices were irradiated for another 50Mrads, with three of them taken out after 25Mrads during the second stage. The second part is lower-dose irradiations with total doses of up to 2Mrads. The temperature throughout the irradiation process was monitored to be below 30°C.

We present new normally off GaN high-electron-mobility transistors (HEMTs) that overcome the typical limitations in multi-mesa-channel (MMC) width through modulation of the via-hole-length to regulate the charge neutrality screen effect. We have prepared enhancement-mode (E-mode) GaN HEMTs having widths of up to 300 nm, based on an enhanced surface pinning effect. E-mode GaN HEMTs having MMC structures and widths as well as via-hole-lengths of 100 nm/2 μm and 300 nm/6 μm, respectively, exhibited positive threshold voltages (Vth) of 0.79 and 0.46 V, respectively. The on-resistances of the MMC and via-hole-length structures were lower than those of typical tri-gate nanoribbon GaN HEMTs. In addition, the devices not only achieved the E-mode but also improved the power performance of the GaN HEMTs and effectively mitigated the device thermal effect. We controlled the via-hole-length sidewall surface pinning effect to obtain the E-mode GaN HEMTs. Our findings suggest that via-hole-length normally off GaN HEMTs have great potential for use in next-generation power electronics.

GaN high electron mobility transistors (HEMTs) on SiC substrates are produced for both commercial and defense applications that require high voltage, high power, and high efficiency operation. Although leading GaN HEMT manufacturers have reported excellent RF power characteristics and encouraging reliability, long-term reliability in the space environment remains a major concern due to unknown degradation mechanisms. For the present study, we investigated stressed/degraded RF GaN HEMTs using micro-analytical techniques. Our RF AlGaN-GaN devices grown on SiC substrate had a Ni-Pd-Au Schottky gate length of 0.25 μm, a total gate width of 6 × 150 μm periphery, and a field plate. First, we performed DC bias-temperature stress tests on GaN HEMTs and some GaN HEMTs were thermally stressed as monitor samples. Second, we employed focused ion beam (FIB) to prepare TEM cross sections from degraded and monitor devices for defect analysis using a high resolution TEM. Defects containing highly Pd-enriched features were found at the edge of the drain side of the gate. We present our detailed analysis results including our understanding on the out-diffusion of Pd as a potential degradation mechanism in our RF devices.

Compared with silicon, GaN has advantages such as high electron mobility large band gap and high breakdown field strength. Therefore, GaN High Electron Mobility Transistors (HEMT) is resistant to high voltage and high temperature, and GaN HEMT performs well in high-frequency and high-power fields. Enhancement mode GaN HEMT is more suitable for most applications than depletion mode GaN HEMT due to enhancement mode GaN HEMT’s normally-off characteristic. This paper introduces cascode structure GaN HEMT and p-GaN gate structure GaN HEMT, as well as two improved structures, monolithically integrated Si-GaN cascoded FET and Hybrid Drain embedded Gate Injection Transistor, then compares the four structures and analyzes the advantages and disadvantages. Because of the unique advantages of GaN HEMT, many industries that require the use of high-frequency devices or high-power devices are very interested in the application research of GaN HEMT. This paper mainly introduces the research progress of GaN HEMT’s application in the three fields of radio frequency amplifiers, charger circuits, and LiDAR drivers, and the paper summarizes the advantages and current challenges of GaN HEMT, as well as the future of GaN HEMT’s development and application.

In order to achieve high‐performance gallium nitride (GaN) high‐electron‐mobility‐transistors (HEMTs) capable of operating in the X‐band, a bilayer passivation technique is employed. The technique involves creating a stacked passivation layer consisting of a 20‐nm Si‐rich silicon nitride (SixN) passivation layer and a 100‐nm N‐rich silicon nitride (Si3N4) passivation layer. This effectively reduces radio frequency scattering in GaN HEMTs without compromising the breakdown voltage (BV). On the one hand, the SixN passivation layer effectively suppresses the surface states of devices, resulting in low current collapse. On the other hand, the Si3N4 passivation layer can effectively reduce gate leakage caused by the SixN passivation layer, allowing the device to reliably operate at higher voltages. Consequently, a GaN HEMTs with SixN/Si3N4 bilayer passivation achieve a low current collapse of 5% and a high BV of 157 V. The device features a current gain cutoff frequency (fT) and maximum oscillation frequency (fmax) of 57.9 and 96.8 GHz, respectively. Additionally, it exhibits excellent radio frequency performance in the X‐band, with an output power density (Pout) of 13.7 W mm−1 and power added efficiency of 60.8% at a drain voltage (VD) bias of 50 V.

Summary form only given. Wide band gap semiconductor of GaN and its related materials are promising for future power and high frequency applications. In particular, the GaN high electron mobility transistor (HEMT) grown on large-size Si substrate is suitable for low-lost and high power switching applications. The GaN HEMT could be fabricated into convertors and invertors for electrified vehicle (EV). In order to achieve GaN HEMT device with high efficiency, various issues have to be considered. These include the careful design of material structure and device layout. Furthermore, surface passivation techniques are critical for reducing dynamic on-resistance (R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</sub> ) and improving reliability. For safety purpose, a normally-off device is required. Thus, the pros and cons of normally-off device fabrication approaches such as gate-recessed, p-GaN cap and F-plasma treatment will be discussed. The possibility of using fully-copper-based metallization will also be addressed. The copper metallization can reduce the fabrication cost effectively by replacing the conventional gold metallization. Finally, power module is demonstrated by employing the GaN HEMTs and Schottky barrier diodes. For future RF power application, GaN HEMTs on SiC substrate are fabricated. The GaN material grown on SiC can achieve better crystal quality and the HEMT devices are also beneficial from better thermal dissipation due to high thermal conductivity SiC substrate. GaN HEMT on SiC could be used in future high frequency applications such as formilitary phased array radar and civilian 4 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> -generation base station. Besides the AlGaN/GaN HEMT structure, new material structures such as InAlN/GaN and AlN/GaN are also demonstrated. These structures have great potential for very high frequency (>300 GHz) and high power applications.

This paper reports a high-performance microwave receiver protector (RP) based on a single gallium nitride (GaN) high electron mobility transistor (HEMT) at an operation frequency of 30 to 3000 MHz. The HEMT-based RP exhibits multi features: high power compression, constant output power, tunable threshold power level, and insensitivity to frequency variation. With a low drain voltage (Vds) of 3 V, constant output power of 9.9 dBm was acquired for input power over its threshold power of 3.2 dBm. Power compression of 13.3 dB was achieved at the input power of Pin = 20 dBm. In addition, adjustable threshold power level Pth could be obtained by merely tuning drain voltage. Transducer gain measurement results were employed to explain the occurrence of output power saturation. Relatively higher Pth was linked to wider gate voltage swing which extended the linear region of the Pout-Pin characteristic. In addition, the GaN HEMT’s power compression capability shows great immunity to frequency variation, which is promising for protecting sensitive receiver components at both low and high frequencies. Finally, the phase shift of the GaN HEMT RP at high input power was measured and analyzed by the nonlinear behaviors of input capacitance Cgs.

The swift implementation of 5G networks has escalated the need for high-performance radio frequency (RF) components, especially within the sub-6 GHz region. Low Noise Amplifiers (LNAs) are essential in 5G receiver systems, where concurrently attaining acceptable noise figure, gain, and stability poses a considerable difficulty. This study tackles these problems through a comparative examination of two promising transistor technologies for LNA design at 3.5 GHz: Gallium Nitride (GaN) High Electron Mobility Transistor (HEMT) and Indium Gallium Phosphide (InGaP) Heterojunction Bipolar Transistor (HBT). Two LNA circuits were designed and simulated using Advanced Design System (ADS) software: one employing the CG2H40025 GaN HEMT and the other utilizing the MMG3006NT1 InGaP HBT. Simulation results indicate that the GaN HEMT-based LNA attained a gain of 17.09 dB, a noise figure of 1.299 dB, and a stability factor of 1.083, whereas the InGaP HBT-based LNA exhibited a gain of 17.84 dB, a noise figure of 1.906 dB, and a stability factor of 1.255. This comparative analysis offers significant insights into the advantages and compromises of each technology for 5G LNA architecture. According to these findings, GaN HEMT technology is favored for its enhanced noise performance, rendering it more appropriate for noise-sensitive 5G sub-6 GHz applications, although its somewhat reduced gain. This analysis provides a pragmatic reference for RF engineers in choosing the optimal transistor technology for particular 5G sub-6 GHz LNA design specifications.

Fifth generation communication networks promise extremely high data throughputs, low latencies, and ultra-high reliability by employing small cells in high density networks. This will increase the use of highly inefficient microwave power amplifiers, that exhibit efficiencies sometimes as low as 10% for advanced multi-carrier waveforms. To overcome these inefficiencies and enable next generation technology development, the internal distributed behaviour of the packaged microwave power transistor has to be fully characterised, which is impossible using conventional port-based measurements. In this dissertation, the development of a set of multiphysics measurement techniques that capture the distributed electrical, electromagnetic, and thermal device behaviour is described. These new multiphysics measurement techniques enable the characterisation and direct visualisation of the inefficient device performance, providing a basis for future design optimisation. The techniques combine a non-linear vector network analyser, electro-optic, load-pull and thermoreflectance measurement systems that enable large signal time-domain electrical, distributed multi-harmonic vector electric field (E-field), and transient and steady-state thermal measurements. The multiphysics measurement set-up was used to characterise various transistors and PAs including 260 W silicon (Si) laterally diffused metal oxide semiconductor (LDMOS) field effect transistors in both air-cavity ceramic and plastic packages, 25 W gallium nitride (GaN) on silicon carbide high electron mobility transistors (HEMTs), 250 W GaN HEMT and 360 W Si LDMOS Doherty power amplifiers. The E-field measurements enabled the first ever imaging of parametric odd-mode oscillations within multi-die packaged high-power microwave transistors. Additionally, the measurement system was used to verify the effectiveness of in-package oscillation suppression circuits. As high-resolution E-field measurements can be slow, a surrogate modelling-based measurement algorithm was implemented to accelerate measurements 10-fold. Transient thermal measurements helped to identify abnormal transistor finger-to-finger heating in GaN HEMTs and revealed thermal differences along the gate width in GaN-based asymmetric transistors for Doherty power amplifier applications.

With Gallium Nitride (GaN) device technology for power electronics applications being ramped up for volume production, an increasing amount of research is now focused on the performance of GaN power devices in circuits. In this study, an enhancement mode GaN high electron mobility transistor (HEMT) is switched in a clamped inductive switching configuration with the aim of investigating the source of oscillatory effects observed. These arise as a result of the increased switching speed capability of GaN devices compared to their silicon counterparts. The study identifies the two major mechanisms (Miller capacitance charge and parasitic common source inductance) that can lead to ringing behaviour during turn-off and considers the effect of temperature on the latter. Furthermore, the experimental results are backed by SPICE modelling to evaluate the contribution of different circuit components to oscillations. The study concludes with good design techniques that can suppress the effects discussed.

This article has presented a unified electrothermal behavior modeling method for both silicon carbide (SiC) metal oxide semiconductor field effect transistor ( <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mosfet</small> ) and gallium nitride (GaN) high electron mobility transistor (HEMT). The electrothemal behavior of these two kind of devices in both the first and the third quadrant is accurately modeled with serval compact equations. A modeling data and optimization algorithm-based parameter extraction method have been proposed to replace the previous time consuming and labor intensive one. The proposed parameter fitting algorithm is a genetic algorithm and Levenberg–Marquardt combined optimization algorithm possessing the advantages of global optimization and fast convergence speed, and modeling data can come from both datasheets and measurement. The correctness and accuracy of the proposed modeling method has been verified by simulation and experiment result. Meanwhile, it has been proved that the proposed modeling method is applicable to several commercially available SiC <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mosfet</small> s and GaN HEMTs.