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Amorphous Oxide Semiconductors

IGZO and Related Materials for Display and Memory

Hosono, Hideo / Kumomi, Hideya (Editor)

Wiley Series in Display Technology

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1. Edition June 2022
640 Pages, Hardcover
Wiley & Sons Ltd

ISBN: 978-1-119-71557-3
John Wiley & Sons

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AMORPHOUS OXIDE SEMICONDUCTORS

A singular resource on amorphous oxide semiconductors edited by a world-recognized pioneer in the field

In Amorphous Oxide Semiconductors: IGZO and Related Materials for Display and Memory, the Editors deliver a comprehensive account of the current status of--and latest developments in--transparent oxide semiconductor technology. With contributions from leading international researchers and exponents in the field, this edited volume covers physical fundamentals, thin-film transistor applications, processing, circuits and device simulation, display and memory applications, and new materials relevant to amorphous oxide semiconductors.

The book makes extensive use of structural diagrams of materials, energy level and energy band diagrams, device structure illustrations, and graphs of device transfer characteristics, photographs and micrographs to help illustrate the concepts discussed within. It also includes:
* A thorough introduction to amorphous oxide semiconductors, including discussions of commercial demand, common challenges faced during their manufacture, and materials design
* Comprehensive explorations of the electronic structure of amorphous oxide semiconductors, structural randomness, doping limits, and defects
* Practical discussions of amorphous oxide semiconductor processing, including oxide materials and interfaces for application and solution-process metal oxide semiconductors for flexible electronics
* In-depth examinations of thin film transistors (TFTs), including the trade-off relationship between mobility and reliability in oxide TFTs

Perfect for practicing scientists, engineers, and device technologists working with transparent semiconductor systems, Amorphous Oxide Semiconductors: IGZO and Related Materials for Display and Memory will also earn a place in the libraries of students studying oxides and other non-classical and innovative semiconductor devices.

WILEY SID Series in Display Technology

Series Editor: Ian Sage, Abelian Services, Malvern, UK

The Society for Information Display (SID) is an international society which has the aim of encouraging the development of all aspects of the field of information display. Complementary to the aims of the society, the Wiley-SID series is intended to explain the latest developments in information display technology at a professional level. The broad scope of the series addresses all facets of information displays from technical aspects through systems and prototypes to standards and ergonomics.

Preface xv

Series Editor's Foreword xvii

About the Editors xviii

List of Contributors xix

Part I Introduction 1

1.1 Transparent Amorphous Oxide Semiconductors for Display Applications 3
Hideo Hosono

1.1.1 Introduction to Amorphous Semiconductors as Thin-Film Transistor (TFT) Channels 3

1.1.2 Historical Overview 4

1.1.3 Oxide and Silicon 6

1.1.4 Transparent Amorphous Oxide Semiconductors 6

1.1.4.1 Electronic Structures 6

1.1.4.2 Materials 8

1.1.4.3 Characteristic Carrier Transport Properties 9

1.1.4.4 Electronic States 10

1.1.5 P-Type Oxide Semiconductors for Display Applications 13

1.1.5.1 Oxides of Transition Metal Cations with an Electronic Configuration of (n.1)d 10 ns 0 (n = 4or5) 13

1.1.5.2 Oxides of Metal Cations with an Electronic Configuration of ns 2 13

1.1.5.3 Oxides of Metal Cations with an Electronic Configuration of nd 6 14

1.1.6 Novel Amorphous Oxide Semiconductors 15

1.1.7 Summary and Outlook 17

References 18

1.2 Transparent Amorphous Oxide Semiconductors 21
Hideya Kumomi

1.2.1 Introduction 21

1.2.2 Technical Issues and Requirements of TFTs for AM-FPDs 21

1.2.2.1 Field-Effect Mobility 21

1.2.2.2 Off-State Leakage Current and On/Off Current Ratio 23

1.2.2.3 Stability and Reliability 23

1.2.2.4 Uniformity 23

1.2.2.5 Large-Area Devices by Large-Area Mother-Glass Substrates 24

1.2.2.6 Low-Temperature Fabrication and Flexibility 24

1.2.3 History, Features, Uniqueness, Development, and Applications of AOS-TFTs 24

1.2.3.1 History 24

1.2.3.2 Features and Uniqueness 25

1.2.3.3 Applications 27

1.2.3.4 Development and Products of AM-FPDs 28

1.2.4 Summary 29

References 30

Part II Fundamentals 31

2 Electronic Structure and Structural Randomness 33
Julia E. Medvedeva, Bishal Bhattarai, and D. Bruce Buchholz

2.1 Introduction 33

2.2 Brief Description of Methods and Approaches 35

2.2.1 Computational Approach 35

2.2.2 Experimental Approach 36

2.3 The Structure and Properties of Crystalline and Amorphous In 2 O 3 36

2.4 The Structure and Properties of Crystalline and Amorphous SnO 2 43

2.5 The Structure and Properties of Crystalline and Amorphous ZnO 46

2.6 The Structure and Properties of Crystalline and Amorphous Ga 2 O 3 52

2.7 Role of Morphology in Structure-Property Relationships 57

2.8 The Role of Composition in Structure-Property Relationships: IGO and IGZO 64

2.9 Conclusions 69

References 70

3 Electronic Structure of Transparent Amorphous Oxide Semiconductors 73
John Robertson and Zhaofu Zhang

3.1 Introduction 73

3.2 Mobility 73

3.3 Density of States 74

3.4 Band Structures of n-Type Semiconductors 78

3.5 Instabilities 81

3.6 Doping Limits and Finding Effective Oxide Semiconductors 86

3.7 OLED Electrodes 88

3.8 Summary 89

References 89

4 Defects and Relevant Properties 93
Toshio Kamiya, Kenji Nomura, Keisuke Ide, and Hideo Hosono

4.1 Introduction 93

4.2 Typical Deposition Condition 93

4.3 Overview of Electronic Defects in AOSs 94

4.4 Origins of Electron Donors 96

4.5 Oxygen- and Hydrogen-Related Defects and Near-VBM States 98

4.6 Summary 102

References 102

5 Amorphous Semiconductor Mobility Physics and TFT Modeling 105
John F. Wager

5.1 Amorphous Semiconductor Mobility: An Introduction 105

5.2 Diffusive Mobility 106

5.3 Density of States 110

5.4 TFT Mobility Considerations 111

5.5 TFT Mobility Extraction, Fitting, and Model Validation 112

5.6 Physics-Based TFT Mobility Modeling 118

5.7 Conclusions 121

References 122

6 Percolation Description of Charge Transport in Amorphous Oxide Semiconductors: Band Conduction Dominated by Disorder 125
A. V. Nenashev, F. Gebhard, K. Meerholz, and S. D. Baranovskii

6.1 Introduction 125

6.2 Band Transport via Extended States in the Random-Barrier Model (RBM) 126

6.2.1 Deficiencies of the Rate-Averaging Approach: Electrotechnical Analogy 127

6.2.2 Percolation Approach to Charge Transport in the RBM 129

6.3 Random Band-Edge Model (RBEM) for Charge Transport in AOSs 131

6.4 Percolation Theory for Charge Transport in the RBEM 133

6.4.1 From Regional to Global Conductivities in Continuum Percolation Theory 133

6.4.2 Averaging Procedure by Adler et al. 135

6.5 Comparison between Percolation Theory and EMA 136

6.6 Comparison with Experimental Data 137

6.7 Discussion and Conclusions 140

6.7.1 Textbook Description of Charge Transport in Traditional Crystalline Semiconductors (TCSs) 140

6.7.2 Results of This Chapter for Charge Transport in Amorphous Oxide Semiconductors (AOSs) 141

Acknowledgments 141

References 141

7 State and Role of Hydrogen in Amorphous Oxide Semiconductors 145
Hideo Hosono and Toshio Kamiya

7.1 Introduction 145

7.2 Concentration and Chemical States 145

7.3 Carrier Generation and Hydrogen 150

7.3.1 Carrier Generation by H Injection at Low Temperatures 150

7.3.2 Carrier Generation and Annihilation by Thermal Treatment 151

7.4 Energy Levels and Electrical Properties 153

7.5 Incorporation and Conversion of H Impurities 154

7.6 Concluding Remarks 155

Acknowledgments 156

References 156

Part III Processing 159

8 Low-Temperature Thin-Film Combustion Synthesis of Metal-Oxide Semiconductors: Science and Technology 161
Binghao Wang, Wei Huang, Antonio Facchetti, and Tobin J. Marks

8.1 Introduction 161

8.2 Low-Temperature Solution-Processing Methodologies 162

8.2.1 Alkoxide Precursors 162

8.2.2 Microwave-Assisted Annealing 165

8.2.3 High-Pressure Annealing 165

8.2.4 Photonic Annealing 165

8.2.4.1 Laser Annealing 166

8.2.4.2 Deep-Ultraviolet Illumination 168

8.2.4.3 Flash Lamp Annealing 170

8.2.5 Redox Reactions 170

8.3 Combustion Synthesis for MO TFTs 171

8.3.1 n-Type MO TFTs 172

8.3.2 p-Type MO TFTs 178

8.4 Summary and Perspectives 180

Acknowledgments 180

References 181

9 Solution-Processed Metal-Oxide Thin-Film Transistors for Flexible Electronics 185
Hyun Jae Kim

9.1 Introduction 185

9.2 Fundamentals of Solution-Processed Metal-Oxide Thin-Film Transistors 187

9.2.1 Deposition Methods for Solution-Processed Oxide Semiconductors 187

9.2.1.1 Coating-Based Deposition Methods 190

9.2.1.2 Printing-Based Deposition Methods 191

9.2.2 The Formation Mechanism of Solution-Processed Oxide Semiconductor Films 194

9.3 Low-Temperature Technologies for Active-Layer Engineering of Solution-Processed Oxide TFTs 196

9.3.1 Overview 196

9.3.2 Solution Modulation 197

9.3.2.1 Alkoxide Precursors 198

9.3.2.2 pH Adjustment 199

9.3.2.3 Combustion Reactions 199

9.3.2.4 Aqueous Solvent 199

9.3.3 Process Modulation 201

9.3.3.1 Photoactivation Process 201

9.3.3.2 High-Pressure Annealing (HPA) Process 202

9.3.3.3 Microwave-Assisted Annealing Process 204

9.3.3.4 Plasma-Assisted Annealing Process 204

9.3.4 Structure Modulation 205

9.3.4.1 Homojunction Dual-Active or Multiactive Layer 206

9.3.4.2 Heterojunction Dual- or Multiactive Layer 206

9.4 Applications of Flexible Electronics with Low-Temperature Solution-Processed Oxide TFTs 208

9.4.1 Flexible Displays 208

9.4.2 Flexible Sensors 208

9.4.3 Flexible Integrated Circuits 209

References 209

10 Recent Progress on Amorphous Oxide Semiconductor Thin-Film Transistors Using the Atomic Layer Deposition Technique 213
Hyun-Jun Jeong and Jin-Seong Park

10.1 Atomic Layer Deposition (ALD) for Amorphous Oxide Semiconductor (AOS) Applications 213

10.1.1 The ALD Technique 213

10.1.2 Research Motivation for ALD AOS Applications 215

10.2 AOS-TFTs Based on ALD 217

10.2.1 Binary Oxide Semiconductor TFTs Based on ALD 217

10.2.1.1 ZnO-TFTs 217

10.2.1.2 InOx-TFTs 218

10.2.1.3 SnOx-TFTs 218

10.2.2 Ternary and Quaternary Oxide Semiconductor TFTs Based on ALD 220

10.2.2.1 Indium-Zinc Oxide (IZO) and Indium-Gallium Oxide (IGO) 220

10.2.2.2 Zinc-Tin Oxide (ZTO) 223

10.2.2.3 Indium-Gallium-Zinc Oxide (IGZO) 223

10.2.2.4 Indium-Tin-Zinc Oxide (ITZO) 226

10.3 Challenging Issues of AOS Applications Using ALD 226

10.3.1 p-Type Oxide Semiconductors 226

10.3.1.1 Tin Monoxide (SnO) 228

10.3.1.2 Copper Oxide (cu x O) 229

10.3.2 Enhancing Device Performance: Mobility and Stability 230

10.3.2.1 Composition Gradient Oxide Semiconductors 230

10.3.2.2 Two-Dimensional Electron Gas (2DEG) Oxide Semiconductors 231

10.3.2.3 Spatial and Atmospheric ALD for Oxide Semiconductors 234

References 234

Part IV Thin-Film Transistors 239

11 Control of Carrier Concentrations in AOSs and Application to Bulk-Accumulation TFTs 241
Suhui Lee and Jin Jang

11.1 Introduction 241

11.2 Control of Carrier Concentration in a-IGZO 242

11.3 Effect of Carrier Concentration on the Performance of a-IGZO TFTs with a Dual-Gate Structure 247

11.3.1 Inverted Staggered TFTs 247

11.3.2 Coplanar TFTs 251

11.4 High-Drain-Current, Dual-Gate Oxide TFTs 252

11.5 Stability of Oxide TFTs: PBTS, NBIS, HCTS, Hysteresis, and Mechanical Strain 259

11.6 TFT Circuits: Ring Oscillators and Amplifier Circuits 266

11.7 Conclusion 270

References 270

12 Elevated-Metal Metal-Oxide Thin-Film Transistors: A Back-Gate Transistor Architecture with Annealing-Induced Source/Drain Regions 273
Man Wong, Zhihe Xia, and Jiapeng li

12.1 Introduction 273

12.1.1 Semiconducting Materials for a TFT 274

12.1.1.1 Amorphous Silicon 274

12.1.1.2 Low-Temperature Polycrystalline Silicon 274

12.1.1.3 MO Semiconductors 275

12.1.2 TFT Architectures 276

12.2 Annealing-Induced Generation of Donor Defects 279

12.2.1 Effects of Annealing on the Resistivity of IGZO 279

12.2.2 Microanalyses of the Thermally Annealed Samples 283

12.2.3 Lateral Migration of the Annealing-Induced Donor Defects 284

12.3 Elevated-Metal Metal-Oxide (EMMO) TFT Technology 286

12.3.1 Technology and Characteristics of IGZO EMMO TFTs 287

12.3.2 Applicability of EMMO Technology to Other MO Materials 291

12.3.3 Fluorinated EMMO TFTs 292

12.3.4 Resilience of Fluorinated MO against Hydrogen Doping 296

12.3.5 Technology and Display Resolution Trend 298

12.4 Enhanced EMMO TFT Technologies 301

12.4.1 3-EMMO TFT Technology 302

12.4.2 Self-Aligned EMMO TFTs 307

12.5 Conclusion 309

Acknowledgments 310

References 310

13 Hot Carrier Effects in Oxide-TFTs 315
Mami N. Fujii, Takanori Takahashi, Juan Paolo Soria Bermundo, and Yukiharu Uraoka

13.1 Introduction 315

13.2 Analysis of Hot Carrier Effect in IGZO-TFTs 315

13.2.1 Photoemission from IGZO-TFTs 315

13.2.2 Kink Current in Photon Emission Condition 318

13.2.3 Hot Carrier-Induced Degradation of a-IGZO-TFTs 318

13.3 Analysis of the Hot Carrier Effect in High-Mobility Oxide-TFTs 322

13.3.1 Bias Stability under DC Stresses in a High-Mobility IWZO-TFT 322

13.3.2 Analysis of Dynamic Stress in Oxide-TFTs 323

13.3.3 Photon Emission from the IWZO-TFT under Pulse Stress 323

13.4 Conclusion 328

References 328

14 Carbon-Related Impurities and NBS Instability in AOS-TFTs 333
Junghwan Kim and Hideo Hosono

14.1 Introduction 333

14.2 Experimental 334

14.3 Results and Discussion 334

14.4 Summary 337

References 339

Part V TFTs and Circuits 341

15 Oxide TFTs for Advanced Signal-Processing Architectures 343
Arokia Nathan, Denis Striakhilev, and Shuenn-Jiun Tang

15.1 Introduction 343

15.1.1 Device-Circuit Interactions 343

15.2 Above-Threshold TFT Operation and Defect Compensation: AMOLED Displays 345

15.2.1 AMOLED Display Challenges 345

15.2.2 Above-Threshold Operation 347

15.2.3 Temperature Dependence 347

15.2.4 Effects of Process-Induced Spatial Nonuniformity 349

15.2.5 Overview of External Compensation for AMOLED Displays 351

15.3 Ultralow-Power TFT Operation in a Deep Subthreshold (Near Off-State) Regime 354

15.3.1 Schottky Barrier TFTs 355

15.3.2 Device Characteristics and Small Signal Parameters 358

15.3.3 Common Source Amplifier 360

15.4 Oxide TFT-Based Image Sensors 362

15.4.1 Heterojunction Oxide Photo-TFTs 362

15.4.2 Persistent Photocurrent 364

15.4.3 All-Oxide Photosensor Array 365

References 366

16 Device Modeling and Simulation of TAOS-TFTs 369
Katsumi Abe

16.1 Introduction 369

16.2 Device Models for TAOS-TFTs 369

16.2.1 Mobility Model 369

16.2.2 Density of Subgap States (DOS) Model 371

16.2.3 Self-Heating Model 372

16.3 Applications 373

16.3.1 Temperature Dependence 373

16.3.2 Channel-Length Dependence 373

16.3.3 Channel-Width Dependence 375

16.3.4 Dual-Gate Structure 378

16.4 Reliability 379

16.5 Summary 381

Acknowledgments 381

References 382

17 Oxide Circuits for Flexible Electronics 383
Kris Myny, Nikolaos Papadopoulos, Florian De Roose, and Paul Heremans

17.1 Introduction 383

17.2 Technology-Aware Design Considerations 383

17.2.1 Etch-Stop Layer, Backchannel Etch, and Self-Aligned Transistors 384

17.2.1.1 Etch-Stop Layer 384

17.2.1.2 Backchannel Etch 385

17.2.1.3 Self-Aligned Transistors 385

17.2.1.4 Comparison 386

17.2.2 Dual-Gate Transistors 386

17.2.2.1 Stack Architecture 386

17.2.2.2 Effect of the Backgate 388

17.2.3 Moore's Law for TFT Technologies 389

17.2.3.1 Cmos 389

17.2.3.2 Thin-Film Electronics Historically 389

17.2.3.3 New Drivers for Thin-Film Scaling: Circuits 390

17.2.3.4 L-Scaling 391

17.2.3.5 W and L Scaling 391

17.2.3.6 Overall Lateral Scaling 391

17.2.3.7 Oxide Thickness and Supply Voltage Scaling 391

17.2.4 Conclusion 392

17.3 Digital Electronics 392

17.3.1 Communication Chips 392

17.3.2 Complex Metal-Oxide-Based Digital Chips 395

17.4 Analog Electronics 396

17.4.1 Thin-Film ADC Topologies 396

17.4.2 Imager Readout Peripherals 397

17.4.3 Healthcare Patches 399

17.5 Summary 400

Acknowledgments 400

References 400

Part VI Display and Memory Applications 405

18 Oxide TFT Technology for Printed Electronics 407
Toshiaki Arai

18.1 OLEDs 407

18.1.1 OLED Displays 407

18.1.2 Organic Light-Emitting Diodes 408

18.1.3 Printed OLEDs 409

18.2 TFTs for OLED Driving 413

18.2.1 TFT Candidates 413

18.2.2 Pixel Circuits 413

18.2.3 Oxide TFTs 414

18.2.3.1 Bottom-Gate TFTs 415

18.2.3.2 Top-Gate TFTs 418

18.3 Oxide TFT-Driven Printed OLED Displays 424

18.4 Summary 427

References 428

19 Mechanically Flexible Nonvolatile Memory Thin-Film Transistors Using Oxide Semiconductor Active Channels on Ultrathin Polyimide Films 431
Sung-Min Yoon, Hyeong-Rae Kim, Hye-Won Jang, Ji-Hee Yang, Hyo-Eun Kim, and Sol-Mi Kwak

19.1 Introduction 431

19.2 Fabrication of Memory TFTs 432

19.2.1 Substrate Preparation 432

19.2.2 Device Fabrication Procedures 434

19.2.3 Characterization Methodologies 435

19.3 Device Operations of Flexible Memory TFTs 437

19.3.1 Optimization of Flexible IGZO-TFTs on PI Films 437

19.3.2 Nonvolatile Memory Operations of Flexible Memory TFTs 438

19.3.3 Operation Mechanisms and Device Physics 442

19.4 Choice of Alternative Materials 444

19.4.1 Introduction to Conducting Polymer Electrodes 444

19.4.2 Introduction of Polymeric Gate Insulators 446

19.5 Device Scaling to Vertical-Channel Structures 447

19.5.1 Vertical-Channel IGZO-TFTs on PI Films 447

19.5.2 Vertical-Channel Memory TFTs Using IGZO Channel and ZnO Trap Layers 449

19.6 Summary 453

19.6.1 Remaining Technical Issues 453

19.6.2 Conclusions and Outlooks 453

References 454

20 Amorphous Oxide Semiconductor TFTs for BEOL Transistor Applications 457
Nobuyoshi Saito and Keiji Ikeda

20.1 Introduction 457

20.2 Improvement of Immunity to H 2 Annealing 458

20.3 Increase of Mobility and Reduction of S/D Parasitic Resistance 463

20.4 Demonstration of Extremely Low Off-State Leakage Current Characteristics 467

References 471

21 Ferroelectric-HfO 2 Transistor Memory with IGZO Channels 473
Masaharu Kobayashi

21.1 Introduction 473

21.2 Device Operation and Design 475

21.3 Device Fabrication 478

21.4 Experimental Results and Discussions 479

21.4.1 FE-HfO 2 Capacitors with an IGZO Layer 479

21.4.2 IGZO Channel FeFETs 481

21.5 Summary 484

Acknowledgments 484

References 485

22 Neuromorphic Chips Using AOS Thin-Film Devices 487
Mutsumi Kimura

22.1 Introduction 487

22.2 Neuromorphic Systems with Crosspoint-Type alpha-GTO Thin-Film Devices 488

22.2.1 Neuromorphic Systems 488

22.2.1.1 alpha-GTO Thin-Film Devices 488

22.2.1.2 System Architecture 489

22.2.2 Experimental Results 492

22.3 Neuromorphic System Using an LSI Chip and alpha-IGZO Thin-Film Devices [24] 493

22.3.1 Neuromorphic System 494

22.3.1.1 Neuron Elements 494

22.3.1.2 Synapse Elements 494

22.3.1.3 System Architecture 495

22.3.2 Working Principle 495

22.3.2.1 Cellular Neural Network 495

22.3.2.2 Tug-of-War Method 497

22.3.2.3 Modified Hebbian Learning 497

22.3.2.4 Majority-Rule Handling 498

22.3.3 Experimental Results 498

22.3.3.1 Raw Data 498

22.3.3.2 Associative Memory 499

22.4 Conclusion 499

Acknowledgments 500

References 500

23 Oxide TFTs and Their Application to X-Ray Imaging 503
Robert A. Street

23.1 Introduction 503

23.2 Digital X-Ray Detection and Imaging Modalities 504

23.2.1 Indirect Detection Imaging 504

23.2.2 Direct Detection Imaging 505

23.2.3 X-Ray Imaging Modalities 505

23.3 Oxide-TFT X-Ray Detectors 506

23.3.1 TFT Backplane Requirements for Digital X-Rays 506

23.3.2 An IGZO Detector Fabrication and Characterization 506

23.3.3 Other Reported Oxide X-Ray Detectors 509

23.4 How Oxide TFTs Can Improve Digital X-Ray Detectors 509

23.4.1 Noise and Image Quality in X-Ray Detectors 510

23.4.2 Minimizing Additive Electronic Noise with Oxides 510

23.4.3 Pixel Amplifier Backplanes 511

23.4.4 IGZO-TFT Noise 511

23.5 Radiation Hardness of Oxide TFTs 513

23.6 Oxide Direct Detector Materials 515

23.7 Summary 515

References 515

Part VII New Materials 519

24 Toward the Development of High-Performance p-Channel Oxide-TFTs and All-Oxide Complementary Circuits 521
Kenji Nomura

24.1 Introduction 521

24.2 Why Is High-Performance p-Channel Oxide Difficult? 521

24.3 The Current Development of p-Channel Oxide-TFTs 524

24.4 Comparisons of p-Type Cu 2 O and SnO Channels 526

24.5 Comparisons of the TFT Characteristics of Cu 2 O and SnO-TFTs 529

24.6 Subgap Defect Termination for p-Channel Oxides 532

24.7 All-Oxide Complementary Circuits 534

24.8 Conclusions 535

References 536

25 Solution-Synthesized Metal Oxides and Halides for Transparent p-Channel TFTs 539
Ao Liu, Huihui Zhu, and Yong-Young Noh

25.1 Introduction 539

25.2 Solution-Processed p-Channel Metal-Oxide TFTs 540

25.3 Transparent Copper(I) Iodide (CuI)-Based TFTs 546

25.4 Conclusions and Perspectives 548

Acknowledgments 549

References 549

26 Tungsten-Doped Active Layers for High-Mobility AOS-TFTs 553
Zhang Qun

26.1 Introduction 553

26.2 Advances in Tungsten-Doped High-Mobility AOS-TFTs 555

26.2.1 a-IWO-TFTs 555

26.2.2 a-IZWO-TFTs 562

26.2.3 Dual Tungsten-Doped Active-Layer TFTs 565

26.2.4 Treatment on the Backchannel Surface 566

26.3 Perspectives for High-Mobility AOS Active Layers 570

References 572

27 Rare Earth- and Transition Metal-Doped Amorphous Oxide Semiconductor Phosphors for Novel Light-Emitting Diode Displays 577
Keisuke Ide, Junghwan Kim, Hideo Hosono, and Toshio Kamiya

27.1 Introduction 577

27.2 Eu-Doped Amorphous Oxide Semiconductor Phosphor 577

27.3 Multiple-Color Emissions from Various Rare Earth-Doped AOS Phosphors 579

27.4 Transition Metal-Doped AOS Phosphors 582

References 584

28 Application of AOSs to Charge Transport Layers in Electroluminescent Devices 585
Junghwan Kim and Hideo Hosono

28.1 Electronic Structure and Electrical Properties of Amorphous Oxide Semiconductors (AOSs) 585

28.2 Criteria for Charge Transport Layers in Electroluminescent (EL) Devices 585

28.3 Amorphous Zn-Si-O Electron Transport Layers for Perovskite Light-Emitting Diodes (PeLEDs) 587

28.4 Amorphous In-Mo-O Hole Injection Layers for OLEDs 589

28.5 Perspective 594

References 595

29 Displays and Vertical-Cavity Surface-Emitting Lasers 597
Kenichi Iga

29.1 Introduction to Displays 597

29.2 Liquid Crystal Displays (LCDs) 597

29.2.1 History of LCDs 597

29.2.2 Principle of LCD: The TN Mode 598

29.2.3 Other LC Modes 600

29.2.4 Light Sources 600

29.2.5 Diffusion Plate and Light Guiding Layer 601

29.2.6 Microlens Arrays 601

29.2.7 Short-Focal-Length Projection 602

29.3 Organic EL Display 602

29.3.1 Method (a): Color-Coding Method 603

29.3.2 Method (b): Filter Method 603

29.3.3 Method (c): Blue Conversion Method 603

29.4 Vertical-Cavity Surface-Emitting Lasers 604

29.4.1 Motivation of Invention 604

29.4.2 What Is the Difference? 605

29.4.3 Device Realization 605

29.4.4 Applications 607

29.5 Laser Displays including VCSELs 607

29.5.1 Laser Displays 607

29.5.2 Color Gamut 608

29.5.3 Laser Backlight Method 609

Acknowledgments 610

References 611

Index 613
Hideo Hosono, PHD, is Honorary and Institute Professor at the Tokyo Institute of Technology and distinguished fellow at the National Institute for Materials Science, Japan. He received his doctorate from the Tokyo Metropolitan University in 1982, and his research is focused on the creation of novel electronic functional materials. He is a pioneer of oxide semiconductors including IGZO-TFTs, iron-based superconductors and electrides.

Hideya Kumomi, DR.SCI., is Specially Appointed Professor at the Tokyo Institute of Technology Materials Research Center for Element Strategy, Japan. He received his doctorate from Waseda University in 1996 and his research has been focused on semiconductor materials and devices.

H. Hosono, Tokyo Institute of Technology; H. Kumomi, Tokyo Institute of Technology