Gallium-Nitride Semiconductor Technology and Its Practical Design Challenges in Power Electronics Applications: An Overview

Wide band-gap (WBG) semiconductors technology represents a potential candidate to displace conventional silicon (Si) technology used in power electronics. Between Silicon Carbide (SiC) and Gallium Nitride (GaN) power semiconductors, the latter is the least mature of both technologies, with many open research problems, especially in the aerospace industry. In this paper, we address the design and implementation of a DC/DC converter for a hybrid small unmanned aerial vehicle (UAV) based on GaN technology. Both theoretical and simulation comparisons of Si, SiC and GaN transistors for the converter are presented. The conclusion is that GaN devices are the most appropriate to fulfill converter requirements for the size and weight limitations of the selected UAV. The paper presents a buck converter which handles an input voltage range of 32 V to 40 V and provides a 12 V regulated output and output power up to 60 W. The experimental results carried out on the prototype converter show how promising the GaN technology is for aerospace systems, not only regarding its volume and size, but also its efficiency. Besides, practical implementation details are reported to contribute to the design of small, light and reliable GaN power converters for aeronautics.

The high frequency capability and low on-state losses of Gallium Nitride (GaN) transistors offer the potential to increase converter efficiency and/or reduce heatsink and passive component size. This paper investigates the use of GaN technology to enhance the performance of power factor correction (PFC) and LLC converters for battery charging applications. First the efficiency performance of non-isolated PFC converters using GaN transistors is compared by simulation, the asymmetric bridgeless PFC converter is shown to achieve the best efficiency, with a predicted figure of 99% in a 1MHz, 200W design. The predictions are validated by an experimental prototype using a GS66502B, GaN Systems E-mode GaN transistor. Then the efficiency comparison of the PFC and LLC converter using GaN devices for battery charging applications is included in the paper. The experimental results of the PFC converter with GaN devices are also included. Additionally, this paper includes the analysis and design of a common mode input filter for the GaN-based high frequency converters for battery charging application. The size of both the converters using GaN devices is reduced by 40% than the converters based on Si devices. The switching loss comparison of GaN and Si devices are also included in the paper.

This chapter describes the motivation, scope, and outline of the book. Gallium nitride (GaN) as a wide bandgap material enables compact and efficient power electronics. Since the GaN HEMT a lateral device, the high-voltage GaN switch can be combined with other passive and active devices on the same die. This will enable power management integrated circuits (PMICs) that combine power with sensing and control loop circuits. However, monolithic GaN technology is not yet mature in various aspects including parameter variations and analog performance (matching, etc.). As a main challenge, GaN technology lacks a suitable p-type device. The presented research contributes to the development of solutions for reducing the global electric power consumption as well as the overall cost of offline power converters. The book deals in detail with the following main topics: (1) Introduction into monolithic GaN process technology with a focus on the similarities and differences to traditional silicon technologies. (2) The gate loop challenge with GaN transistors due to tight gate voltage requirements and different approaches to ensure a safe operation. (3) Measurement-based characterization of technology properties for analog, digital, and mixed-signal circuit design. (4) Design and implementation of a monolithic buck converter IC in a 650V e-mode GaN technology. (5) Comparison between the designed GaN-based converter and a commercially available silicon converter based on comprehensive experimental characterization and analysis.KeywordsPower electronicsGaNOffline convertersPersonal electronicsWide bandgapGaN integrationMarket overviewShipping numbersHigh efficiencyGlobal energy consumptionUSB PD

Dynamic ON-resistance ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}_{\text {on}}{)}$ </tex-math></inline-formula> or threshold voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {TH}}{)}$ </tex-math></inline-formula> instability caused by charge trapping is one of the most crucial reliability concerns of some gallium nitride (GaN) high-electron mobility transistors (HEMTs). It has been unclear if this issue can be resolved using an alternative GaN device architecture. This work answers this question by characterizing, for the first time, the dynamic <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R} _{\text {ON}}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {TH}}$ </tex-math></inline-formula> stability of an industrial vertical GaN transistor-NexGen’s 1200-V/70- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{m}\Omega $ </tex-math></inline-formula> fin-channel junction-gate field-effect transistor (JFET), fabricated on 100-mm bulk GaN substrates. A circuit setup is deployed for the in situ measurement of the dynamic <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}_{\text {on}}$ </tex-math></inline-formula> under steady-state switching. The longer term stability of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}_{\text {on}}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {TH}}$ </tex-math></inline-formula> is tested under the prolonged stress of negative gate bias and high drain bias. The vertical GaN JFET shows nearly no <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}_{\text {on}}$ </tex-math></inline-formula> or <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {TH}}$ </tex-math></inline-formula> shift in these tests, which could be attributed to the low defect density of the GaN-on-GaN homoepitaxial growth, the absence of electric field ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${E}$ </tex-math></inline-formula> -field) crowding near the surface, and the minimal charge trapping in the native junction gate. These results present a critical milestone for vertical GaN devices toward power electronics applications.

Gallium nitride (GaN) devices show particular promise for space-rated power conversion applications that rely on MOSFET technology whose performance is severely limited by the radiation hardening processes. Although the number of radiation-hardened (rad-hard) GaN devices is low, the current space-rated selection pool can still yield significant efficiency and power density improvements. However, the context of GaN research is often future-oriented such that the application of GaN to common, proven, space-rated converter designs is rare. The presented work quantifies the performance benefits of market available, space-rated GaN HEMTs over rad-hard MOSFETs for a synchronous forward converter, which remains an extremely popular topology for isolated, medium-power, dc–dc conversion on various satellite systems. Two 75-W, space-rated forward converters were designed, implemented, and benchmarked, with the power switch technology being the single variable of change. By forming Pareto-optimal fronts of the key device metrics, optimal rad-hard MOSFETs were chosen so that the baseline converter performance was considered the best case. The frequency limitations of common, available, rad-hard PWM controllers limited the power density in the GaN and Si converters alike; however, efficiency gains proved sizeable. The GaN-based converter saw a peak efficiency of 86%, which was a 4.54% improvement over the Si baseline. Detailed efficiency and loss differential plots are presented, which show the GaN converter’s reduced sensitivity to the input voltage.

The power, efficiency, and bandwidth performance improvements demonstrated by gallium nitride (GaN) material and technology are currently being utilized by state-of-the-art microwave power amplifiers in the latest generation of radar systems. High-power wide bandgap semiconductors play an important role in radar performance. For example, in a phased array radar, the RF energy is distributed to each element, phase shifted, and then amplified before being radiated. Throughout the 1990s, gallium arsenide (GaAs) had been the semiconductor of choice for efficiently amplifying this signal; however, as the performance requirements of these systems continued to increase to meet ever-growing threats, the industry began turning to GaN as an alternative semiconductor of choice.GaN has a significantly wider bandgap compared to GaAs, and GaN has a higher saturation velocity, a higher breakdown electric field, and better thermal conductivity in comparison to GaAs. As a result, GaN produces a 5× increase in output power over GaAs that enables radars to search 5× the volume in the same time, increase their effective range by 50%, or reduce their size by 50% depending on the specific application. AlGaN/GaN high electron mobility transistors (HEMTs) became the early heterostructure of choice providing RF output densities >6 W/mm at microwave and millimeter wave frequencies and high conductivity SiC substrates with a 7-8× improvement in thermal conductivity became the early substrate of choice. However, significant material and substrate issues needed to be solved before the reliability and yield of GaN transistors were sufficient to meet the stringent needs required in defense systems.Today, GaN power amplifier technology continues to evolve as solutions to push performance higher are sought through material choices resulting in larger current densities, through design changes enabling higher operating voltages, through process and transistor designs providing more efficient operation, and through various material advances to improve heat dissipation. In this presentation we will provide an overview of GaN technology development at Raytheon covering the early motivation, material challenges, and insertions as they relate to the issues faced today.

Gallium nitride (GaN)-based solid state lighting technology has revolutionized the semiconductor industry. The GaN technology has played a crucial role in reducing world energy demand as well as reducing the carbon footprint. As per the reports, the global demand for lighting has reduced around 13% of total energy consumption in 2018. The Department of Energy (USA) has estimated that bright white LED source could reduce their energy consumption for lighting by 29% by 2025. Most of the GaN LEDs are grown in c-direction, and this direction gives high growth rate and good crystal integrity. On the other hand, the c-plane growth induces piezoelectric polarization, which reduces the overall efficiency of LEDs since the last decade researchers round the globe working on III-N material to improve the existing technology and to push the limit of III-V domain. Now, the non-polar and semi-polar grown LEDs are under investigation for improved efficiency. With the recent development, the GaN is not only limited to lighting, but latest innovations also led the development of micro-LEDs, lasers projection and point source. These developments have pushed GaN into the realm of display technology. The miniaturization of the GaN-based micro-LED and integration of GaN on silicon driving the application into fast response photonic integrated circuits (ICs). Most of the recent advancements in GaN LED field would be discussed in detail.

The Gallium Nitride (GaN) devices have been attractive due to its low loss and high switching speed. With the soft switching, for example critical mode operation, the GaN converter can be further pushed over MHz range. How to design the critical mode inductor at such switching frequency is a challenge, because the loss on the inductor is a big concern for the converter efficiency. This paper experimentally and numerically evaluates different core materials and structures, winding types and structures. The best candidate can reduce the inductor loss below 3W for a 1kW critical mode converter operating at 1MHz.

This paper presents the analysis and design of gallium nitride (GaN) devices based flyback converter. It is critical to optimize power loop and gate loop for flyback converter due to high dv/dt of GaN device. EPC devices with 200V/12A were used in flyback converter. Because GaN device has no avalanche voltage and is sensitive to gate voltage, one need pay more attention to design of gate driver and selection snubber circuits. Different snubber circuits for GaN based flyback converter were compared in this paper. Magnetics selection for high frequency (HF) transformer was discussed in view of size, frequency, turn ratio and loss. A detailed power loss breakdown has been executed with core loss, cooper loss, leakage inductance loss, conduction loss and switching loss. Performance, such as current/voltage stress, voltage spike, efficiency, ect., were analyzed and compared under continuous conduction mode (CCM), boundary conduction mode (BCM), discontinuous conduction mode (DCM), and BCM with valley switching. Experimental results show highest efficiency is achieved under BCM with valley switching.

Gallium Nitride (GaN) and Silicon Carbide (SiC) power devices are segmented in the Wide Bandgap (WBG) device market: GaN devices are suitable for high-frequency but low-voltage applications; SiC devices are suitable for low-frequency but high-voltage applications. Cascoding a GaN HEMT and a SiC JFET best utilizes the advantages of both of these WBG power devices. Like GaN devices, the cascode GaN/SiC device is easy to drive at high frequencies and has low gate loss; like SiC devices, it also has relatively high voltage rating and low C oss energy loss at high frequencies. In previous studies, power circuits using the cascode device achieved higher power density than circuits using only a SiC device but efficiency similar to that of a SiC device [1]. In this paper, we present our investigation of the gate loss mechanism of the SiC JFET in the cascode structure and our finding that the loss can be greatly reduced by minimizing the gate resistance of the SiC JFET (R g,Jfet ). Simulation results showed that reducing R g,Jfet from 6 Ω to 1 Ω at 13.56 MHz leads to a 5× loss reduction, and experimental data verified the simulation trend. Here we provide a simple guideline to optimize the cascode GaN/SiC device and achieve better performance in high-frequency and high-voltage applications.

To address the accuracy limitations of the traditional double pulse test (DPT) for measuring switching losses in high-speed gallium nitride (GaN) devices and the slow measurement speed of conventional calorimetric methods, this paper proposes a fast and accurate calorimetric-based method for characterizing GaN switching losses. Compared to DPT, this method allows rapid and faithful measurement of switching losses under both soft- and hard-switching conditions. A testing measurement platform was developed, which confirmed that this method can collect temperature data in 5 minutes or less by characterizing the switching losses of top-side cooled GaN devices. Achieve a measurement error of less than 9% compared to DPT. It can be used as a supplementary method to verify the accuracy of DPT. The combination of the two methods can achieve cross-validation, significantly improving the reliability of GaN device switching loss measurement results.

This letter presents a novel technology for the integration of gallium nitride (GaN) power devices with silicon control circuits. It comprises stacked GaN power transistors and bipolar-CMOS-double-diffused metal-oxide-semiconductor (DMOS) (BCD) circuits. It leverages on both advantages of the high-voltage low-loss GaN devices and the high-integration BCD circuits. Using conventional manufacturing, packaging, and assembly techniques and equipment, the proposed technology is technology transferrable and applicable for commercial power electronic applications. To validate the concept, a 3.3–70 V dc–dc boost converter is designed, implemented, and verified experimentally. It features a conversion efficiency of 70.3%, output power of 1.68 W, and compact size of ${\text{0.32}}\times {\text{0.18}}\,{\text{cm}}^{2}$ .

Gallium nitride (GaN) is becoming a mainstream semiconductor for power and radio-frequency (RF) applications. While commercial GaN devices are increasingly being adopted in data centers, electric vehicles, consumer electronics, telecom and defense applications, their performance is still far from the intrinsic GaN limit. In the last few years, the fin field-effect transistor (FinFET) and trigate architectures have been leveraged to develop a new generation of GaN power and RF devices, which have continuously advanced the state-of-the-art in the area of microwave and power electronics. Very different from Si digital FinFET devices, GaN FinFETs have allowed for numerous structural innovations based on engineering the two-dimensional-electron gas or p–n junctions, in both lateral and vertical architectures. The superior gate controllability in these fin-based GaN devices has not only allowed higher current on/off ratio, steeper threshold swing, and suppression of short-channel effects, but also enhancement-mode operation, on-resistance reduction, current collapse alleviation, linearity improvement, higher operating frequency, and enhanced thermal management. Several GaN FinFET and trigate device technologies are close to commercialization. This review paper presents a global overview of the reported GaN FinFET and trigate device technologies for RF and power applications, as well as provides in-depth analyses correlating device design parameters to device performance space. The paper concludes with a summary of current challenges and exciting research opportunities in this very dynamic research field.

The load cycling capability of novel power semiconductors is an important aspect when estimating their lifetime in field service. The Power Cycling Test (PCT) is the standard test to evaluate the lifetime of a semiconductor device under thermo-mechanical stress. PCTs are typically performed at temperature swings (ΔT) much higher than common operating conditions, to obtain results within a reasonable time. In this work, the PCT capability of gallium nitride (GaN) and gallium oxide (Ga2O3) lateral transistors is investigated. The GaN devices were tested in two groups with different ΔT. The temperature of the devices was monitored using two different temperature sensitive electrical parameters (TSEPs) and the accuracy of both methods was evaluated by comparing the results with the temperature, monitored by using an infrared (IR) camera. For Ga2O3 devices, no data on potential TSEP exists so far, thus, the typical TSEP for silicon (Si), silicon carbide (SiC) and GaN were investigated for their applicability to Ga2O3 devices. While a PCT was conducted on the devices, the temperature was also monitored using an IR camera. The results of the comparison of TSEP and IR camera data showed, that the accuracy of the TSEP for GaN matched either the temperature of the hottest spot on the chip (VDS method), or the average chip temperature (VGS method). For the Ga2O3 devices no suitable TSEP could be obtained and only the IR camera was used for the temperature measurement. It revealed a very uneven temperature and thus, current distribution on the chip. Furthermore, both GaN and Ga2O3 devices exhibit an outstanding power cycling capability with no failure after completing several millions of cycles. Considering the difference in Young’s Modulus of Si, GaN and Ga2O3, the PCT performance of GaN on silicon devices and Ga2O3 devices should be inferior to silicon devices. Thus, both device types, the GaN transistors and the Ga2O3 transistors, showed a PCT capability much higher than expected.

Gallium nitride (GaN) devices are widely used due to their excellent performance when integrated into power electronics applications. However, owing to their low parasitic parameters and fast switching speed, they are more prone to instability than the silicon devices. The sustained oscillation discussed in this article is one of the instability problems, which may result in overshoot or even more serious device breakdown; thus, it is pretty necessary to suppress it effectively in practical applications. It is the first time to adopt an RC snubber to suppress the sustained oscillation in this article, which is very simple and cheap but effective. First, the sustained oscillation modeling based on a double pulse circuit is carried out. Then, the RC region is established quantitatively according to the root locus analysis results, which makes up for the defects of these qualitative methods before. Furthermore, it is first found that the sustained oscillation can be fully suppressed due to the existence of dipoles. Finally, the oscillation suppression effect within the RC region is compared with that outside the region by the simulation and experimental results, which are consistent with the theoretical analysis. Additionally, the possible negative influence of the added RC snubber is also discussed in this article, which shows that it has a little impact on the switching speed and energy loss, while the sustained oscillation is well suppressed.