Characterization Methodology, Modeling, and Converter Design for 600 V Enhancement-Mode GaN FETs

Gallium Nitride (GaN) power devices are an emerging technology that have only become available commercially in the past few years. This new technology enables the design of converters at higher frequencies and efficiencies than those achievable with conventional Si devices. This dissertation reviews the unique characteristics, commercial status, and design challenges that surround GaN FETs, in order to provide sufficient background to potential GaN-based converter designers.Methodology for experimentally characterizing a GaN FET was also presented, including static characterization with a curve tracer and impedance analyzer, as well as dynamic characterization in a double pulse test setup. This methodology was supplemented by additional tests to determine losses caused by Miller-induced cross talk, and the tradeoff between these losses and overlap losses was studied for one example device.Based on analysis of characterization results, a simplified model was developed to describe the overall switching behavior and some unique features of the device. The impact of the Miller effect during the turn-on transient was studied, as well as the dynamic performance of GaN at elevated temperature.Furthermore, solutions were proposed for several key design challenges in GaN-based converters. First, a driver-integrated overcurrent and short-circuit protection scheme was developed, based on the relationship between gate voltage and drain current in GaN gate injection transistors. Second, the limitations on maximum utilization of current and voltage in a GaN FET were studied, particularly the voltage overshoots following turn-on and turn-off switching transients, and the effective cooling of GaN FETs in higher power operation. A thermal design was developed for heat extraction from bottom-cooled surface-mount devices. These solutions were verified in a GaN-based full-bridge single-phase inverter

Modeling and simulation of bulk gallium nitride power semiconductor devices

Bulk gallium nitride (GaN) power semiconductor devices are gaining significant interest in recent years, creating the need for technology computer aided design (TCAD) simulation to accurately model and optimize these devices. This paper comprehensively reviews and compares different GaN physical models and model parameters in the literature, and discusses the appropriate selection of these models and parameters for TCAD simulation. 2-D drift-diffusion semi-classical simulation is carried out for 2.6 kV and 3.7 kV bulk GaN vertical PN diodes. The simulated forward current-voltage and reverse breakdown characteristics are in good agreement with the measurement data even over a wide temperature range

Мощные СВЧ-транзисторы на основе широкозонных полупроводников

Представлен обзор опубликованных в последние годы результатов по созданию мощных СВЧ-транзисторов на основе гетероструктур AlGaN/GaN. Рассмотрены вопросы конструкции и технологии изготовления данных транзисторов, результаты исследований влияния подложки на характеристики приборов. Показано, что НЕМТ на основе гетероструктур AlGaN/GaN могут обеспечивать 5—10-кратное увеличение удельной мощности (≥10 Вт/мм) при кпд до 60%, увеличение рабочих температур, повышение надежности по сравнению с приборами на основе GaAs.The review of the outcomes, published per last years, on creation of UHF power transistors on AlGaN/GaN heterostructures is submitted. The problems of a design and technology of manufacturing of the transistors as well as an influence of a substrate on the characteristics of devices are surveyed. Is exhibited, that AlGaN/GaN НЕМТs can provide (5-10) multiple increases of power density (≥10 W/mm) at an efficiency up to 60 %, increase of operation temperatures, reliability increasing as compared to GaAs devices

Gallium nitride-based microwave high-power heterostructure field-effect transistors

The research described in this thesis has been carried out within a joint project between the Radboud Universiteit Nijmegen (RU) and the Technische Universiteit Eindhoven (TU/e) with the title: "Performance enhancement of GaN-based microwave power amplifiers: material, device and design issues". This project has been granted by the Dutch Technology Foundation STW under project number NAF 5040. The aims of this project have been to develop the technology required to grow state-of-the-art AlGaN/GaN epilayers on sapphire and semi-insulating (s.i.) SiC substrates using metal organic chemical vapor deposition (MOCVD) and to fabricate microwave (f > 1 GHz) high-power (Pout > 10 W) heterostructure field-effect transistors (HFETs) on these epitaxial films. MOCVD growth of AlGaN/GaN epilayers and material characterization has been done within the group Applied Materials Science (AMS) of RU. Research at the Opto-Electronic Devices group (OED) of TU/e has focused on both electrical characterization of AlGaN/GaN epilayers and design, process technology development, and characterization of GaN-based HFETs and CPW passive components. Although a considerable amount of work has been done during this research with respect to processing of CPW passive components on s.i. SiC substrates, this thesis focused on active AlGaN/GaN devices only. GaN is an excellent option for high-power/high-temperature microwave applications because of its high electric breakdown field (3 MV/cm) and high electron saturation velocity (1.5 x 107 cm/s). The former is a result of the wide bandgap (3.44 eV at RT) and enables the application of high supply voltages (> 50 V), which is one of the two requirements for highpower device performance. In addition, the wide bandgap allows the material to withstand much higher operating temperatures (300oC - 500oC) than can the conventional semiconductor materials such as Si, GaAs, and InP. A big advantage of GaN over SiC is the possibility to grow heterostructures, e.g. AlGaN/GaN. The resulting two-dimensional electron gas (2DEG) at the AlGaN/GaN heterojunction serves as the conductive channel. Large drain currents (> 1 A/mm), which are the second requirement for a power device, can be achieved because of the high electron sheet densities (> 1 x 1013 cm-2) and high electron saturation velocity. These material properties clearly indicate why GaN is a very suitable candidate for next-generation microwave high-power/high-temperature applications such as high-power amplifiers (HPAs) for GSM base stations, and microwave monolithic integrated circuits (MMICs) for radar systems. In this thesis we have presented the design, technology, and measurement results of n.i.d. AlGaN/GaN:Fe HFETs grown on s.i. 4H-SiC substrates by MOCVD. These devices have submicrometer T- or FP-gates with a gate length (Lg) of 0.7 µm and total gate widths (Wg) of 0.25 mm, 0.5 mm, and 1.0 mm, respectively. The 1.0 mm devices are capable of producing a maximum microwave output power (Pout) of 11.9 W at S-band (2 GHz - 4 GHz) using class AB bias conditions of VDS = 50 V and VGS = -4.65 V. It has to be noted that excellent scaling of Pout with Wg has been demonstrated. In addition, the associated power gain (Gp) ranges between 15 dB and 20 dB, and for the power added efficiency (PAE) values from 54 % up to 70 % have been obtained. These results clearly illustrate both the successful development of the MOCVD growth process, and the successful development and integration of process modules such as ohmic and Schottky contact technology, device isolation, electron beam lithography, surface passivation, and air bridge technology, into a process flow that enables the fabrication of state-of-the-art large periphery n.i.d. AlGaN/GaN:Fe HFETs on s.i. SiC substrates, which are perfectly suitable for application in e.g. HPAs at S-band

Review and Characterization of Gallium Nitride Power Devices

Gallium Nitride (GaN) power devices are an emerging technology that have only recently become available commercially. This new technology enables the design of converters at higher frequencies and efficiencies than those achievable with conventional Si devices. This thesis reviews the characteristics and commercial status of both vertical and lateral GaN power devices from the user perspective, providing the background necessary to understand the significance of these recent developments. Additionally, the challenges encountered in GaN-based converter design are considered, such as the consequences of faster switching on gate driver design and board layout. Other issues include the unique reverse conduction behavior, dynamic on-resistance, breakdown mechanisms, thermal design, device availability, and reliability qualification. Static and dynamic characterization was then performed across the full current, voltage, and temperature range of this device to enable effective GaN-based converter design. Static testing was performed with a curve tracer and precision impedance analyzer. A double pulse test setup was constructed and used to measure switching loss and time at the fastest achievable switching speed, and the subsequent overvoltages due to the fast switching were characterized. The results were also analyzed to characterize the effects of cross-talk in the active and synchronous devices of a phase-leg topology with enhancement-mode GaN HFETs. Based on these results and analysis, an accurate loss model was developed for the device under test. Based on analysis of these characterization results, a simplified model was developed to describe the overall switching behavior and some unique features of the device. The consequences of the Miller effect during the turn-on transient were studied to show that no Miller plateau occurs, but rather a decreased gate voltage slope, followed by a sharp drop. The significance of this distinction is derived and explained. GaN performance at elevated temperature was also studied, because turn-on time increases significantly with temperature, and turn-on losses increase as a result. Based on this relationship, a temperature-dependent turn-on model and a linear scaling factor was proposed for estimating turn-on loss in e-mode GaN HFETs

Optimization of off-state breakdown voltage in GaN high-electron-mobility transistors

Gallium nitride (GaN) technology is the next revolution in electronics as it offers a large bandgap (high critical electric field) and high electron mobility (2D electron gas) in one transistor design, surpassing silicon (Si), gallium arsenide (GaAs), and indium phosphide (InP) based technologies. High efficiency and high voltage operation of GaN high electron mobility transistors (HEMTs) provide significant performance and size advantages over the aforementioned devices. GaN HEMTs are normally-on devices, meaning that the devices do not shut down even though no gate voltage is applied, due to the 2D electron gas channel. In applications where safety and efficiency are in the forefront, normally-off devices are preferred. A simple way to obtain a normally-off GaN HEMT is to apply a negative gate voltage. A challenge of normally-off GaN HEMT is that the devices usually fail before the critical electric field is reached. Breakdown is caused by gate-leakage impact-ionization, drain-to-source punchthrough and vertical current leakage. Increasing the breakdown voltage would eliminate the damage in high voltage, high current applications and would extend the lifetime and operating bias conditions. The goal of this research is to design and simulate GaN-based power transistors in order to understand their different characteristics, such as voltage-current relations, using TCAD Sentaurus software. GaN HEMTs with different design strategies (i.e. doping concentration, layer thicknesses, layer contents) are simulated in order to understand their impact on off-state breakdown voltages. Based on the simulation results, different strategies to improve the off-state breakdown voltage are proposed.Ope

Failure Physics and Reliability of GaN-Based HEMTs for Microwave and Millimeter-Wave Applications: A Review of Consolidated Data and Recent Results

Herein, the results are reviewed concerning reliability of high-electron mobility transistors (HEMTs) based on GaN, which currently represent the technology of choice for high-efficiency microwave and millimeter-wave power amplifiers. Several failure mechanisms of these devices are extensively studied, including converse piezoelectric effects, formation of conductive percolation paths at the edge of gate toward the drain, surface oxidation of GaN, time-dependent breakdown of GaN buffer, and of field-plate dielectric. For GaN HEMTs with scaled gate length, the simultaneous control of short-channel effects, deep-level dispersion, and hot-electron-induced degradation requires a careful optimization of epitaxial material quality and device design

TCAD device modelling and simulation of wide bandgap power semiconductors

Technology computer-aided Design (TCAD) is essential for devices technology development, including wide bandgap power semiconductors. However, most TCAD tools were originally developed for silicon and their performance and accuracy for wide bandgap semiconductors is contentious. This chapter will deal with TCAD device modelling of wide bandgap power semiconductors. In particular, modelling and simulating 3C- and 4H-Silicon Carbide (SiC), Gallium Nitride (GaN) and Diamond devices are examined. The challenges associated with modelling the material and device physics are analyzed in detail. It also includes convergence issues and accuracy of predicted performance. Modelling and simulating defects, traps and the effect of these traps on the characteristics are also discussed

A design strategy for AM/PM compensation in GaN Doherty power amplifiers

This paper presents the theoretical analysis of phase distortion (AM/PM) mechanisms in Gallium Nitride (GaN) Doherty power amplifiers (DPAs) and a novel approach to optimize the tradeoff between linearity and efficiency. In particular, it is demonstrated how it is possible to mitigate the AM/PM by designing a suitable mismatch at the input of the active devices, based on the identification of constant AM/PM and gain contour circles. The proposed theory is experimentally confirmed by source- and load-pull measurements and further validated through the design and realization of a 7 GHz 10 W DPA based on GaN monolithic technology

Robust Control of Wide Bandgap Power Electronics Device Enabled Smart Grid

abstract: In recent years, wide bandgap (WBG) devices enable power converters with higher power density and higher efficiency. On the other hand, smart grid technologies are getting mature due to new battery technology and computer technology. In the near future, the two technologies will form the next generation of smart grid enabled by WBG devices. This dissertation deals with two applications: silicon carbide (SiC) device used for medium voltage level interface (7.2 kV to 240 V) and gallium nitride (GaN) device used for low voltage level interface (240 V/120 V). A 20 kW solid state transformer (SST) is designed with 6 kHz switching frequency SiC rectifier. Then three robust control design methods are proposed for each of its smart grid operation modes. In grid connected mode, a new LCL filter design method is proposed considering grid voltage THD, grid current THD and current regulation loop robust stability with respect to the grid impedance change. In grid islanded mode, µ synthesis method combined with variable structure control is used to design a robust controller for grid voltage regulation. For grid emergency mode, multivariable controller designed using H infinity synthesis method is proposed for accurate power sharing. Controller-hardware-in-the-loop (CHIL) testbed considering 7-SST system is setup with Real Time Digital Simulator (RTDS). The real TMS320F28335 DSP and Spartan 6 FPGA control board is used to interface a switching model SST in RTDS. And the proposed control methods are tested. For low voltage level application, a 3.3 kW smart grid hardware is built with 3 GaN inverters. The inverters are designed with the GaN device characterized using the proposed multi-function double pulse tester. The inverter is controlled by onboard TMS320F28379D dual core DSP with 200 kHz sampling frequency. Each inverter is tested to process 2.2 kW power with overall efficiency of 96.5 % at room temperature. The smart grid monitor system and fault interrupt devices (FID) based on Arduino Mega2560 are built and tested. The smart grid cooperates with GaN inverters through CAN bus communication. At last, the three GaN inverters smart grid achieved the function of grid connected to islanded mode smooth transitionDissertation/ThesisDoctoral Dissertation Electrical Engineering 201