Physics and Technology of Crystalline Oxide Semiconductor CAAC-IGZO

Shunpei Yamazaki, Semiconductor Energy Laboratory Co., Ltd., Kanagawa, JAPAN Dr. Shunpei Yamazaki is an authority on semiconductors, memory devices, and liquid crystal displays. Listed on over 4,000 US utility patents, Dr. Yamazaki was named in the Guinness Book of World Records as holding the most patents in the world; hailed the most prolific inventor in history by USA Today (in 2005). His most notable work is on the thin-film transistor -- a significant discovery being a crystalline structure in Indium gallium zinc oxide (IGZO) material, which he discovered "by chance" in 2009. Today Dr. Yamazaki is President of the Semiconductor Energy Laboratory (SEL), where he and his team pioneered the unique development of ultra-low-power devices using CAAC-IGZO technology. A joint venture with the Sharp Corporation manufacturing smartphones using crystalline oxide semiconductors (IGZO) is a global first. In 2015 Dr.Yamazaki received the SID (Society for Information Display) Special Recognition Award for "discovering CAAC-IGZO semiconductors, leading its practical application, and paving the way to next-generation displays." His paper on CAAC-IGZO ranked in the top 15 most downloaded papers of Wiley Electrical Engineering and Communications Technology journals, 2014. Dr. Yamazaki is also an IEEE Life Fellow. Tetsuo Tsutsui, Kyushu University, Japan Tetsuo Tsutsui received his BS (1967) and MS (1969) in Applied Chemistry from Kyushu University, Japan, and Dr. of Engineering in Materials Science from Graduate School of Engineering Sciences of the same university in 1977. He was a professor at Graduate School of Engineering Sciences, Kyushu University from 1986 to 2008. His research interests were electronic and optical properties of molecular solids and organic semiconductor electronics, including organic light-emitting diodes, organic FETs, and organic photovoltaic devices. He has published more than 200 original and 50 review papers. He received The Polymer Society Award (Polymer Society, Japan, 1995), Chemical Society of Japan Award (2008), Medal with Purple Ribbon (Cabinet Office of the Japanese Government, 2009), and Jan Rajchman Prize (Society for Information Displays, 2011). He is a Fellow of Japan Society of Applied Physics and a Professor Emeritus, Kyushu University.

About the Editors ix

List of Contributors xi

Series Editor’s Foreword xiii

Preface xv

Acknowledgments xviii

1 Introduction 1

1.1 History of Displays 3

1.2 Requirement for Displays 4

1.3 Transistor Technology for Displays 5

1.3.1 Comparison of Silicon and Oxide Semiconductors 6

1.3.2 FETs in LCDs 8

1.3.3 FETs in OLED Displays 11

1.3.4 Recent FET Technologies 14

1.3.5 Development of OLED Displays 17

References 19

2 Applications of CAAC-IGZO FETs to Displays 21

2.1 Introduction 21

2.2 Bottom-Gate Top-Contact FET 24

2.2.1 Manufacturing Process for CAAC-IGZO FETs with C.E.-Type BGTC Structure 27

2.2.2 GI Formation 27

2.2.3 Formation of Buried Channel by Stacked Active Layer 33

2.2.4 Baking Treatment of CAAC-IGZO 42

2.2.5 Damaged Layer (n-Type) Formed by Deposition of S/D Electrodes 45

2.2.6 Cleaning of the Back Channel 47

2.2.7 Copper Wiring for S/D Electrodes 52

2.3 Top-Gate Self-Aligned FET 62

2.3.1 Fabrication Process of TGSA CAAC-IGZO FETs 64

2.3.2 Formation of GE/GI Patterns 65

2.3.3 Formation of S/D Regions 66

2.3.4 GI Thinning and L Reduction 70

2.4 Characteristics of CAAC-IGZO FET 71

2.4.1 Current Drivability 71

2.4.2 Low Off-State Current 94

2.4.3 Normally-Off Id–Vg Characteristics and Small Threshold-Voltage Variation 98

2.4.4 Saturability of Id–Vd Characteristics 103

2.4.5 Summary 109

2.5 Density of States and Device Reliability 109

2.5.1 Introduction 110

2.5.2 Measurement of Defect States in IGZO Film 111

2.5.3 Correlation between Oxygen Vacancies and FET Characteristics 115

2.5.4 Defect States in Silicon-Oxide Film 117

2.5.5 NBITS Mechanism 122

2.5.6 Summary 122

2.6 Oxide Conductor Electrode Process 124

2.6.1 Introduction 124

2.6.2 Method of Fabricating Oxide Conductor Electrode and Measurements of its Resistivity 124

2.6.3 LCD Device with Oxide Conductor Electrode 131

2.6.4 Summary 134

References 135

3 Driver Circuit 138

3.1 Introduction 138

3.2 Gate-Driver Circuit 139

3.2.1 Logic Circuit and Bootstrapping 139

3.2.2 Flip-Flops 141

3.2.3 Reduction in Area of Gate-Driver Circuit 149

3.3 Source-Driver Circuit 154

3.3.1 Introduction 154

3.3.2 Demultiplexer 157

3.3.3 8-Bit Source-Driver IC for 13.3-Inch, 60-Hz, 8-Bit 8 K OLED Panels 161

3.3.4 12-Bit Source-Driver IC for 13.3-Inch, 120-Hz, 12-Bit 8 K OLED Panels 172

3.3.5 Full-Driver IC 179

References 181

4 Application to OLED Displays 183

4.1 Introduction 183

4.2 Device Architecture for High-Performance OLED 185

4.2.1 Fundamentals of OLEDs 185

4.2.2 Organic Material/Metal Oxide Composite 201

4.2.3 Exciplex–Triplet Energy Transfer for High-Performance Phosphorescent OLEDs 221

4.2.4 Enhancement in the Emission Efficiency of Fluorescent OLEDs 240

4.2.5 Increase in Outcoupling Efficiency of OLEDs by Molecular Orientation 253

4.3 OLED Structure for Higher Pixel Density 261

4.3.1 Tandem OLED 262

4.3.2 WTC Structure 269

4.3.3 Measures for Crosstalk 272

4.4 Circuit Design for OLED Displays 274

4.4.1 Driving OLED Displays 274

4.4.2 External Compensation 280

4.4.3 Internal Compensation 282

4.4.4 Arrangement of Pixel Circuit and High Resolution 291

4.5 Characteristics of OLED Displays 293

4.5.1 Application of WTC Structure to Displays 293

4.5.2 Performance of OLED and LCDs 295

References 300

5 Flexible Displays 306

5.1 Introduction 306

5.1.1 OLED and Flexible Displays 306

5.2 Flexible Display Fabrication Technology 309

5.2.1 Separation Layer 309

5.2.2 Separation Process 309

5.2.3 Transfer Process of Flexible Displays 316

5.2.4 Moisture-Blocking Property of the Flexible OLED Display 320

5.2.5 Bending Test 326

5.2.6 System Automation by Transfer Technology Apparatus (TT Apparatus) 328

5.3 Prototypes of Flexible OLED Displays 338

References 347

6 Application to Liquid Crystal Displays 349

6.1 Introduction 349

6.2 Technology for Higher Resolution 351

6.2.1 Introduction 351

6.2.2 The Pixel Circuit 351

6.2.3 Pixel Layout and Aperture Ratio of an LCD 353

6.2.4 Applicability of Large-Sized Displays 355

6.3 Driving Method for Power Saving 358

6.3.1 Introduction 358

6.3.2 Saving Power with Low-Frequency Driving 358

6.3.3 Low-Frequency Driving with CAAC-IGZO 360

6.3.4 Configuration of a Liquid Crystal Cell for Low-Frequency Driving 367

6.3.5 Conclusions 376

6.4 Characteristics of LCDs 376

6.4.1 Introduction 376

6.4.2 High-Resolution Fringe-Field Switching LCDs 376

6.4.3 A 434-PPI Reflective LCD 388

References 395

Appendix 398

Index 400