GaN Transistors for Efficient Power Conversion

An up-to-date, practical guide on upgrading from silicon to GaN, and how to use GaN transistors in power conversion systems design  This updated, third edition of a popular book on GaN transistors for efficient power conversion has been substantially expanded to keep students and practicing power conversion engineers ahead of the learning curve in GaN technology advancements. Acknowledging that GaN transistors are not one-to-one replacements for the current MOSFET technology, this book serves as a practical guide for understanding basic GaN transistor construction, characteristics, and applications. Included are discussions on the fundamental physics of these power semiconductors, layout, and other circuit design considerations, as well as specific application examples demonstrating design techniques when employing GaN devices. GaN Transistors for Efficient Power Conversion, 3rd Edition brings key updates to the chapters of Driving GaN Transistors; Modeling, Simulation, and Measurement of GaN Transistors; DC-DC Power Conversion; Envelope Tracking; and Highly Resonant Wireless Energy Transfer. It also offers new chapters on Thermal Management, Multilevel Converters, and Lidar, and revises many others throughout.  Written by leaders in the power semiconductor field and industry pioneers in GaN power transistor technology and applications Updated with 35% new material, including three new chapters on Thermal Management, Multilevel Converters, Wireless Power, and Lidar Features practical guidance on formulating specific circuit designs when constructing power conversion systems using GaN transistors A valuable resource for professional engineers, systems designers, and electrical engineering students who need to fully understand the state-of-the-art GaN Transistors for Efficient Power Conversion, 3rd Edition is an essential learning tool and reference guide that enables power conversion engineers to design energy-efficient, smaller, and more cost-effective products using GaN transistors. 

Table of Contents:
Foreword xv Acknowledgments xvii 1 GaN Technology Overview 1 1.1 Silicon Power Metal Oxide Silicon Field Effect Transistors 1976–2010 1 1.2 The Gallium Nitride Journey Begins 2 1.3 GaN and SiC Compared with Silicon 2 1.3.1 Bandgap (Eg) 3 1.3.2 Critical Field (Ecrit) 3 1.3.3 On‐Resistance (RDS(on)) 4 1.3.4 The Two‐Dimensional Electron Gas (2DEG) 4 1.4 The Basic GaN Transistor Structure 6 1.4.1 Recessed Gate Enhancement‐Mode Structure 7 1.4.2 Implanted Gate Enhancement‐Mode Structure 8 1.4.3 pGaN Gate Enhancement‐Mode Structure 8 1.4.4 Hybrid Normally Off Structures 8 1.4.5 Reverse Conduction in HEMT Transistors 10 1.5 Building a GaN Transistor 11 1.5.1 Substrate Material Selection 11 1.5.2 Growing the Heteroepitaxy 12 1.5.3 Processing the Wafer 12 1.5.4 Making Electrical Connection to the Outside World 13 1.6 GaN Integrated Circuits 15 1.7 Summary 21 References 21 2 GaN Transistor Electrical Characteristics 25 2.1 Introduction 25 2.2 Device Ratings 25 2.2.1 Drain‐Source Voltage 25 2.3 On‐Resistance (RDS(on)) 30 2.4 Threshold Voltage 33 2.5 Capacitance and Charge 34 2.6 Reverse Conduction 37 2.7 Summary 39 References 40 3 Driving GaN Transistors 41 3.1 Introduction 41 3.2 Gate Drive Voltage 44 3.3 Gate Drive Resistance 45 3.4 Capacitive Current‐Mode Gate Drive Circuits for Gate Injection Transistors 46 3.5 dv/dt Considerations 48 3.5.1 Controlling dv/dt at Turn‐On 48 3.5.2 Complementary Device Turn‐On 49 3.6 di/dt Considerations 51 3.6.1 Device Turn‐On and Common‐Source Inductance 51 3.6.2 Off‐State Device di/dt 53 3.7 Bootstrapping and Floating Supplies 54 3.8 Transient Immunity 57 3.9 High‐Frequency Considerations 59 3.10 Gate Drivers for Enhancement‐Mode GaN Transistors 60 3.11 Cascode, Direct‐Drive, and Higher‐Voltage Configurations 60 3.11.1 Cascode Devices 60 3.11.2 Direct‐Drive Devices 63 3.11.3 Higher‐Voltage Configurations 64 3.12 Summary 64 References 65 4 Layout Considerations for GaN Transistor Circuits 69 4.1 Introduction 69 4.2 Minimizing Parasitic Inductance 69 4.3 Conventional Power‐Loop Designs 72 4.3.1 Lateral Power‐Loop Design 72 4.3.2 Vertical Power‐Loop Design 73 4.4 Optimizing the Power Loop 74 4.4.1 Impact of Integration on Parasitics 75 4.5 Paralleling GaN Transistors 76 4.5.1 Paralleling GaN Transistors for a Single Switch 76 4.5.2 Paralleling GaN Transistors for Half‐Bridge Applications 79 4.6 Summary 83 References 83 5 Modeling and Measurement of GaN Transistors 85 5.1 Introduction 85 5.2 Electrical Modeling 85 5.2.1 Basic Modeling 85 5.2.2 Limitations of Basic Modeling 88 5.2.3 Limitations of Circuit Simulation 90 5.3 Measuring GaN Transistor Performance 91 5.3.1 Voltage Measurement Requirements 94 5.3.2 Probing and Measurement Techniques 96 5.3.3 Measuring Non‐Ground‐Referenced Signals 99 5.3.4 Current Measurement Requirement 100 5.4 Summary 101 References 102 6 Thermal Management 105 6.1 Introduction 105 6.2 Thermal Equivalent Circuits 105 6.2.1 Thermal Resistances in a Lead Frame Package 105 6.2.2 Thermal Resistances in a Chip‐Scale Package 107 6.2.3 Junction‐to‐Ambient Thermal Resistance 108 6.2.4 Transient Thermal Impedance 109 6.3 Improving Thermal Performance with a Heatsink 110 6.3.1 Selection of Heatsink and Thermal Interface Material (TIM) 111 6.3.2 Heatsink Attachment for Bottom‐Side Cooling 112 6.3.3 Heatsink Attachment for Multisided Cooling 113 6.4 System‐Level Thermal Analysis 114 6.4.1 Thermal Model of a Power Stage with Discrete GaN Transistors 115 6.4.2 Thermal Model of a Power Stage with a Monolithic GaN Integrated Circuit 117 6.4.3 Thermal Model of a Multiphase System 118 6.4.4 Temperature Measurement 120 6.4.4.1 Optical 120 6.4.4.2 Physical Contact 121 6.4.4.3 Temperature‐Sensitive Electrical Parameter 122 6.4.5 Experimental Characterization 122 6.4.6 Application Examples 124 6.5 Summary 128 References 128 7 Hard‐Switching Topologies 131 7.1 Introduction 131 7.2 Hard‐Switching Loss Analysis 131 7.2.1 Hard‐Switching Transitions with GaN Transistors 132 7.2.2 Output Capacitance (COSS) Losses 135 7.2.3 Turn‐On Overlap Loss 138 7.2.3.1 Current Rise Time 139 7.2.3.2 Voltage Fall Time 142 7.2.4 Turn‐Off Overlap Losses 145 7.2.4.1 Current Fall Time 146 7.2.4.2 Voltage Rise Time 147 7.2.5 Gate‐Charge (QG) Losses 147 7.2.6 Reverse Conduction Losses (PSD) 147 7.2.6.1 Impact of Dead Time Selection on Reverse Conduction Loss 147 7.2.6.2 Adding an Anti‐Parallel Schottky Diode 150 7.2.6.3 Dynamic COSS‐Related Reverse Conduction Losses 153 7.2.7 Reverse Recovery (QRR) Losses 153 7.2.8 Hard‐Switching Figure of Merit 154 7.3 Impact of Parasitic Inductance on Hard‐Switching Losses 154 7.3.1 Impact of Common‐Source Inductance (LCS) 154 7.3.2 Impact of Power‐Loop Inductance on Device Losses 157 7.4 Frequency Impact on Magnetics 160 7.4.1 Transformers 160 7.4.2 Inductors 161 7.5 Buck Converter Example 162 7.5.1 Comparison with Experimental Measurements 169 7.5.2 Consideration of Parasitic Inductance 170 7.6 Summary 174 References 174 8 Resonant and Soft‐Switching Converters 177 8.1 Introduction 177 8.2 Resonant and Soft‐Switching Techniques 177 8.2.1 Zero‐Voltage and Zero‐Current Switching 177 8.2.2 Resonant DC–DC Converters 179 8.2.3 Resonant Network Combinations 179 8.2.4 Resonant Network Operating Principles 180 8.2.5 Resonant Switching Cells 181 8.2.6 Soft‐Switching DC–DC Converters 182 8.3 Key Device Parameters for Resonant and Soft‐Switching Applications 182 8.3.1 Output Charge (QOSS) 182 8.3.2 Determining Output Charge from Manufacturers’ Datasheets 183 8.3.3 Comparing Output Charge of GaN Transistors and Si MOSFETs 184 8.3.4 Gate Charge (QG) 185 8.3.5 Determining Gate Charge for Resonant and Soft‐Switching Applications 186 8.3.6 Comparing Gate Charge of GaN Transistors and Si MOSFETs 187 8.3.7 Comparing Performance Metrics of GaN Transistors and Si MOSFETs 187 8.4 High‐Frequency Resonant Bus Converter Example 188 8.4.1 Resonant GaN and Si Bus Converter Designs 191 8.4.2 GaN and Si Device Comparison 191 8.4.3 Zero‐Voltage Switching Transition 193 8.4.4 Efficiency and Power Loss Comparison 195 8.4.5 Impact of Further Device Improvements on Performance 197 8.5 Summary 199 References 199 9 RF Performance 201 9.1 Introduction 201 9.2 Differences Between RF and Switching Transistors 202 9.3 RF Basics 204 9.4 RF Transistor Metrics 205 9.4.1 Determining the High‐Frequency Characteristics of RF Transistors 206 9.4.2 Pulse Testing for Thermal Considerations 207 9.4.3 Analyzing the s‐Parameters 209 9.4.3.1 Test for Stability 209 9.4.3.2 Transistor Input and Output Reflection 210 9.4.3.3 Transducer Gain 211 9.4.3.4 Unilateral/Bilateral Transistor Test 211 9.5 Amplifier Design Using Small‐Signal s‐Parameters 212 9.5.1 Conditionally Stable Bilateral Transistor Amplifier Design 213 9.5.1.1 Available Gain 213 9.5.1.2 Constant Available Gain Circles 213 9.6 Amplifier Design Example 214 9.6.1 Matching and Bias Tee Network Design 216 9.6.2 Experimental Verification 219 9.7 Summary 221 References 221 10 DC–DC Power Conversion 223 10.1 Introduction 223 10.2 Non‐Isolated DC–DC Converters 223 10.2.1 The 12 VIN–1.2 VOUT Buck Converter with Discrete Devices 224 10.2.2 The 12 VIN–1 VOUT Monolithic Half‐Bridge IC‐Based Point‐of‐Load Module 228 10.2.3 Very‐High‐Frequency 12 VIN Monolithic Half‐Bridge IC‐Based Point‐of‐Load Module 230 10.2.4 The 28 VIN–3.3 VOUT Point‐of‐Load Module 233 10.2.5 The 48 VIN–12 VOUT Buck Converter with Parallel GaN Transistors for High‐Current Applications 233 10.3 Transformer‐Based DC–DC Converters 239 10.3.1 Eighth‐Brick Converter Example 239 10.3.2 High‐Performance 48 V Step‐Down LLC DC Transformer 243 10.3.2.1 Circuit Overview 243 10.3.2.2 GaN Transistor Advantage in the LLC Converter 244 10.3.2.3 A 1 MHz, 900 W, 48 V–12 V LLC Example Using GaN Transistors 245 10.3.2.4 A 1 MHz, 900 W, 48 V–6 V LLC Example Using GaN Transistors 248 10.4 Summary 249 References 250 11 Multilevel Converters 251 11.1 Introduction 251 11.2 Benefits of Multilevel Converters 251 11.2.1 Applying Multilevel Converters to 48 V Applications 252 11.2.2 Multilevel Converters for High‐Voltage (400 V) Applications 254 11.3 Gate Driver Implementation 255 11.4 Bootstrap Power Supply Solutions for GaN Transistors 256 11.5 Multilevel Converters for PFC Applications 261 11.6 Experimental Examples 263 11.6.1 Low Voltage 263 11.6.2 High Voltage 264 11.7 Summary 264 References 265 12 Class D Audio Amplifiers 269 12.1 Introduction 269 12.1.1 Total Harmonic Distortion 271 12.1.2 Intermodulation Distortion 272 12.2 GaN Transistor Class D Audio Amplifier Example 273 12.2.1 Closed‐Loop Amplifier 274 12.2.2 Open‐Loop Amplifier 276 12.3 Summary 278 References 278 13 Lidar 281 13.1 Introduction to Light Detection and Ranging (Lidar) 281 13.2 Pulsed Laser Driver Overview 281 13.2.1 Pulse Requirements 282 13.2.2 Semiconductor Optical Sources 284 13.2.3 Basic Driver Circuits 285 13.2.4 Driver Switch Properties 286 13.3 Basic Design Process 288 13.3.1 Resonant Capacitive Discharge Laser Driver Design 288 13.3.2 Quantitative Effect of Stray Inductance 289 13.4 Hardware Driver Design 290 13.5 Experimental Results 291 13.5.1 High‐Speed Laser Driver Design Example 291 13.5.2 Fastest 292 13.5.3 Highest Current 293 13.5.4 Low Voltage 293 13.6 Other Considerations 294 13.6.1 Resonant Capacitors 294 13.6.2 Charging 295 13.6.3 Voltage Probing 295 13.6.4 Current Sensing 296 13.6.5 Dual‐Edge Control 297 13.7 Summary 299 References 299 14 Envelope Tracking 301 14.1 Introduction 301 14.2 High‐Frequency GaN Transistors 302 14.3 Topologies for Envelope Tracking Supplies 304 14.3.1 Multiphase Converter 305 14.3.2 Multilevel Converter 306 14.4 Gate Driver Design 307 14.5 Design Example: Tracking a 20 MHz LTE Envelope Signal 308 14.6 Summary 311 References 311 15 Highly Resonant Wireless Power 315 15.1 Introduction 315 15.2 Overview of a Wireless Power System 316 15.3 Amplifiers for Wireless Power Systems 320 15.3.1 The Class E Amplifier 320 15.3.2 ZVS Class D Amplifier 321 15.4 Transistors Suitable for Wireless Power Amplifiers 322 15.4.1 Figure of Merit for Wireless Power Amplifier Topologies 322 15.4.2 GaN Transistors Evaluation in Wireless Power Applications 323 15.5 Experimental Validation of GaN Transistor‐Based Wireless Power Amplifiers 325 15.5.1 Differential‐Mode Class E Amplifier Example 325 15.5.2 Differential‐Mode ZVS Class D Amplifier Example 330 15.6 Summary 334 References 334 16 GaN Transistors for Space Applications 337 16.1 Introduction 337 16.2 Failure Mechanisms 337 16.3 Standards for Radiation Exposure and Tolerance 338 16.4 Gamma Radiation Tolerance 338 16.5 SEE Testing 340 16.6 Neutron Radiation (Displacement Damage) 341 16.7 Performance Comparison Between GaN Transistors and Rad‐Hard Si MOSFETs 343 16.8 Summary 344 References 345 17 Replacing Silicon Power MOSFETs 347 17.1 Introduction: What Controls the Rate of Adoption? 347 17.2 New Capabilities Enabled by GaN Transistors 347 17.3 GaN Transistors are Easy to Use 349 17.4 Cost Versus Time 350 17.4.1 Starting Material 351 17.4.2 Epitaxial Growth 351 17.4.3 Wafer Fabrication 351 17.4.4 Test and Assembly 352 17.5 GaN Transistors are Reliable 352 17.6 Future Direction of GaN Transistors 352 17.7 Summary 353 References 354 Appendix 355 Index 361