Amorphous Oxide Semiconductors

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.

• Preface xvSeries Editor’s Foreword xviiAbout the Editors xviiiList of Contributors xixPart I Introduction 11.1 Transparent Amorphous Oxide Semiconductors for Display Applications 3Hideo Hosono1.1.1 Introduction to Amorphous Semiconductors as Thin-Film Transistor (TFT) Channels 31.1.2 Historical Overview 41.1.3 Oxide and Silicon 61.1.4 Transparent Amorphous Oxide Semiconductors 61.1.4.1 Electronic Structures 61.1.4.2 Materials 81.1.4.3 Characteristic Carrier Transport Properties 91.1.4.4 Electronic States 101.1.5 P-Type Oxide Semiconductors for Display Applications 131.1.5.1 Oxides of Transition Metal Cations with an Electronic Configuration of (n−1)d 10 ns 0 (n = 4or5) 131.1.5.2 Oxides of Metal Cations with an Electronic Configuration of ns 2 131.1.5.3 Oxides of Metal Cations with an Electronic Configuration of nd 6 141.1.6 Novel Amorphous Oxide Semiconductors 151.1.7 Summary and Outlook 17References 181.2 Transparent Amorphous Oxide Semiconductors 21Hideya Kumomi1.2.1 Introduction 211.2.2 Technical Issues and Requirements of TFTs for AM-FPDs 211.2.2.1 Field-Effect Mobility 211.2.2.2 Off-State Leakage Current and On/Off Current Ratio 231.2.2.3 Stability and Reliability 231.2.2.4 Uniformity 231.2.2.5 Large-Area Devices by Large-Area Mother-Glass Substrates 241.2.2.6 Low-Temperature Fabrication and Flexibility 241.2.3 History, Features, Uniqueness, Development, and Applications of AOS-TFTs 241.2.3.1 History 241.2.3.2 Features and Uniqueness 251.2.3.3 Applications 271.2.3.4 Development and Products of AM-FPDs 281.2.4 Summary 29References 30Part II Fundamentals 312 Electronic Structure and Structural Randomness 33Julia E. Medvedeva, Bishal Bhattarai, and D. Bruce Buchholz2.1 Introduction 332.2 Brief Description of Methods and Approaches 352.2.1 Computational Approach 352.2.2 Experimental Approach 362.3 The Structure and Properties of Crystalline and Amorphous In 2 O 3 362.4 The Structure and Properties of Crystalline and Amorphous SnO 2 432.5 The Structure and Properties of Crystalline and Amorphous ZnO 462.6 The Structure and Properties of Crystalline and Amorphous Ga 2 O 3 522.7 Role of Morphology in Structure–Property Relationships 572.8 The Role of Composition in Structure–Property Relationships: IGO and IGZO 642.9 Conclusions 69References 703 Electronic Structure of Transparent Amorphous Oxide Semiconductors 73John Robertson and Zhaofu Zhang3.1 Introduction 733.2 Mobility 733.3 Density of States 743.4 Band Structures of n-Type Semiconductors 783.5 Instabilities 813.6 Doping Limits and Finding Effective Oxide Semiconductors 863.7 OLED Electrodes 883.8 Summary 89References 894 Defects and Relevant Properties 93Toshio Kamiya, Kenji Nomura, Keisuke Ide, and Hideo Hosono4.1 Introduction 934.2 Typical Deposition Condition 934.3 Overview of Electronic Defects in AOSs 944.4 Origins of Electron Donors 964.5 Oxygen- and Hydrogen-Related Defects and Near-VBM States 984.6 Summary 102References 1025 Amorphous Semiconductor Mobility Physics and TFT Modeling 105John F. Wager5.1 Amorphous Semiconductor Mobility: An Introduction 1055.2 Diffusive Mobility 1065.3 Density of States 1105.4 TFT Mobility Considerations 1115.5 TFT Mobility Extraction, Fitting, and Model Validation 1125.6 Physics-Based TFT Mobility Modeling 1185.7 Conclusions 121References 1226 Percolation Description of Charge Transport in Amorphous Oxide Semiconductors: Band Conduction Dominated by Disorder 125A. V. Nenashev, F. Gebhard, K. Meerholz, and S. D. Baranovskii6.1 Introduction 1256.2 Band Transport via Extended States in the Random-Barrier Model (RBM) 1266.2.1 Deficiencies of the Rate-Averaging Approach: Electrotechnical Analogy 1276.2.2 Percolation Approach to Charge Transport in the RBM 1296.3 Random Band-Edge Model (RBEM) for Charge Transport in AOSs 1316.4 Percolation Theory for Charge Transport in the RBEM 1336.4.1 From Regional to Global Conductivities in Continuum Percolation Theory 1336.4.2 Averaging Procedure by Adler et al. 1356.5 Comparison between Percolation Theory and EMA 1366.6 Comparison with Experimental Data 1376.7 Discussion and Conclusions 1406.7.1 Textbook Description of Charge Transport in Traditional Crystalline Semiconductors (TCSs) 1406.7.2 Results of This Chapter for Charge Transport in Amorphous Oxide Semiconductors (AOSs) 141Acknowledgments 141References 1417 State and Role of Hydrogen in Amorphous Oxide Semiconductors 145Hideo Hosono and Toshio Kamiya7.1 Introduction 1457.2 Concentration and Chemical States 1457.3 Carrier Generation and Hydrogen 1507.3.1 Carrier Generation by H Injection at Low Temperatures 1507.3.2 Carrier Generation and Annihilation by Thermal Treatment 1517.4 Energy Levels and Electrical Properties 1537.5 Incorporation and Conversion of H Impurities 1547.6 Concluding Remarks 155Acknowledgments 156References 156Part III Processing 1598 Low-Temperature Thin-Film Combustion Synthesis of Metal-Oxide Semiconductors: Science and Technology 161Binghao Wang, Wei Huang, Antonio Facchetti, and Tobin J. Marks8.1 Introduction 1618.2 Low-Temperature Solution-Processing Methodologies 1628.2.1 Alkoxide Precursors 1628.2.2 Microwave-Assisted Annealing 1658.2.3 High-Pressure Annealing 1658.2.4 Photonic Annealing 1658.2.4.1 Laser Annealing 1668.2.4.2 Deep-Ultraviolet Illumination 1688.2.4.3 Flash Lamp Annealing 1708.2.5 Redox Reactions 1708.3 Combustion Synthesis for MO TFTs 1718.3.1 n-Type MO TFTs 1728.3.2 p-Type MO TFTs 1788.4 Summary and Perspectives 180Acknowledgments 180References 1819 Solution-Processed Metal-Oxide Thin-Film Transistors for Flexible Electronics 185Hyun Jae Kim9.1 Introduction 1859.2 Fundamentals of Solution-Processed Metal-Oxide Thin-Film Transistors 1879.2.1 Deposition Methods for Solution-Processed Oxide Semiconductors 1879.2.1.1 Coating-Based Deposition Methods 1909.2.1.2 Printing-Based Deposition Methods 1919.2.2 The Formation Mechanism of Solution-Processed Oxide Semiconductor Films 1949.3 Low-Temperature Technologies for Active-Layer Engineering of Solution-Processed Oxide TFTs 1969.3.1 Overview 1969.3.2 Solution Modulation 1979.3.2.1 Alkoxide Precursors 1989.3.2.2 pH Adjustment 1999.3.2.3 Combustion Reactions 1999.3.2.4 Aqueous Solvent 1999.3.3 Process Modulation 2019.3.3.1 Photoactivation Process 2019.3.3.2 High-Pressure Annealing (HPA) Process 2029.3.3.3 Microwave-Assisted Annealing Process 2049.3.3.4 Plasma-Assisted Annealing Process 2049.3.4 Structure Modulation 2059.3.4.1 Homojunction Dual-Active or Multiactive Layer 2069.3.4.2 Heterojunction Dual- or Multiactive Layer 2069.4 Applications of Flexible Electronics with Low-Temperature Solution-Processed Oxide TFTs 2089.4.1 Flexible Displays 2089.4.2 Flexible Sensors 2089.4.3 Flexible Integrated Circuits 209References 20910 Recent Progress on Amorphous Oxide Semiconductor Thin-Film Transistors Using the Atomic Layer Deposition Technique 213Hyun-Jun Jeong and Jin-Seong Park10.1 Atomic Layer Deposition (ALD) for Amorphous Oxide Semiconductor (AOS) Applications 21310.1.1 The ALD Technique 21310.1.2 Research Motivation for ALD AOS Applications 21510.2 AOS-TFTs Based on ALD 21710.2.1 Binary Oxide Semiconductor TFTs Based on ALD 21710.2.1.1 ZnO-TFTs 21710.2.1.2 InOx-TFTs 21810.2.1.3 SnOx-TFTs 21810.2.2 Ternary and Quaternary Oxide Semiconductor TFTs Based on ALD 22010.2.2.1 Indium–Zinc Oxide (IZO) and Indium–Gallium Oxide (IGO) 22010.2.2.2 Zinc–Tin Oxide (ZTO) 22310.2.2.3 Indium–Gallium–Zinc Oxide (IGZO) 22310.2.2.4 Indium–Tin–Zinc Oxide (ITZO) 22610.3 Challenging Issues of AOS Applications Using ALD 22610.3.1 p-Type Oxide Semiconductors 22610.3.1.1 Tin Monoxide (SnO) 22810.3.1.2 Copper Oxide (cu x O) 22910.3.2 Enhancing Device Performance: Mobility and Stability 23010.3.2.1 Composition Gradient Oxide Semiconductors 23010.3.2.2 Two-Dimensional Electron Gas (2DEG) Oxide Semiconductors 23110.3.2.3 Spatial and Atmospheric ALD for Oxide Semiconductors 234References 234Part IV Thin-Film Transistors 23911 Control of Carrier Concentrations in AOSs and Application to Bulk-Accumulation TFTs 241Suhui Lee and Jin Jang11.1 Introduction 24111.2 Control of Carrier Concentration in a-IGZO 24211.3 Effect of Carrier Concentration on the Performance of a-IGZO TFTs with a Dual-Gate Structure 24711.3.1 Inverted Staggered TFTs 24711.3.2 Coplanar TFTs 25111.4 High-Drain-Current, Dual-Gate Oxide TFTs 25211.5 Stability of Oxide TFTs: PBTS, NBIS, HCTS, Hysteresis, and Mechanical Strain 25911.6 TFT Circuits: Ring Oscillators and Amplifier Circuits 26611.7 Conclusion 270References 27012 Elevated-Metal Metal-Oxide Thin-Film Transistors: A Back-Gate Transistor Architecture with Annealing-Induced Source/Drain Regions 273Man Wong, Zhihe Xia, and Jiapeng li12.1 Introduction 27312.1.1 Semiconducting Materials for a TFT 27412.1.1.1 Amorphous Silicon 27412.1.1.2 Low-Temperature Polycrystalline Silicon 27412.1.1.3 MO Semiconductors 27512.1.2 TFT Architectures 27612.2 Annealing-Induced Generation of Donor Defects 27912.2.1 Effects of Annealing on the Resistivity of IGZO 27912.2.2 Microanalyses of the Thermally Annealed Samples 28312.2.3 Lateral Migration of the Annealing-Induced Donor Defects 28412.3 Elevated-Metal Metal-Oxide (EMMO) TFT Technology 28612.3.1 Technology and Characteristics of IGZO EMMO TFTs 28712.3.2 Applicability of EMMO Technology to Other MO Materials 29112.3.3 Fluorinated EMMO TFTs 29212.3.4 Resilience of Fluorinated MO against Hydrogen Doping 29612.3.5 Technology and Display Resolution Trend 29812.4 Enhanced EMMO TFT Technologies 30112.4.1 3-EMMO TFT Technology 30212.4.2 Self-Aligned EMMO TFTs 30712.5 Conclusion 309Acknowledgments 310References 31013 Hot Carrier Effects in Oxide-TFTs 315Mami N. Fujii, Takanori Takahashi, Juan Paolo Soria Bermundo, and Yukiharu Uraoka13.1 Introduction 31513.2 Analysis of Hot Carrier Effect in IGZO-TFTs 31513.2.1 Photoemission from IGZO-TFTs 31513.2.2 Kink Current in Photon Emission Condition 31813.2.3 Hot Carrier–Induced Degradation of a-IGZO-TFTs 31813.3 Analysis of the Hot Carrier Effect in High-Mobility Oxide-TFTs 32213.3.1 Bias Stability under DC Stresses in a High-Mobility IWZO-TFT 32213.3.2 Analysis of Dynamic Stress in Oxide-TFTs 32313.3.3 Photon Emission from the IWZO-TFT under Pulse Stress 32313.4 Conclusion 328References 32814 Carbon-Related Impurities and NBS Instability in AOS-TFTs 333Junghwan Kim and Hideo Hosono14.1 Introduction 33314.2 Experimental 33414.3 Results and Discussion 33414.4 Summary 337References 339Part V TFTs and Circuits 34115 Oxide TFTs for Advanced Signal-Processing Architectures 343Arokia Nathan, Denis Striakhilev, and Shuenn-Jiun Tang15.1 Introduction 34315.1.1 Device–Circuit Interactions 34315.2 Above-Threshold TFT Operation and Defect Compensation: AMOLED Displays 34515.2.1 AMOLED Display Challenges 34515.2.2 Above-Threshold Operation 34715.2.3 Temperature Dependence 34715.2.4 Effects of Process-Induced Spatial Nonuniformity 34915.2.5 Overview of External Compensation for AMOLED Displays 35115.3 Ultralow-Power TFT Operation in a Deep Subthreshold (Near Off-State) Regime 35415.3.1 Schottky Barrier TFTs 35515.3.2 Device Characteristics and Small Signal Parameters 35815.3.3 Common Source Amplifier 36015.4 Oxide TFT-Based Image Sensors 36215.4.1 Heterojunction Oxide Photo-TFTs 36215.4.2 Persistent Photocurrent 36415.4.3 All-Oxide Photosensor Array 365References 36616 Device Modeling and Simulation of TAOS-TFTs 369Katsumi Abe16.1 Introduction 36916.2 Device Models for TAOS-TFTs 36916.2.1 Mobility Model 36916.2.2 Density of Subgap States (DOS) Model 37116.2.3 Self-Heating Model 37216.3 Applications 37316.3.1 Temperature Dependence 37316.3.2 Channel-Length Dependence 37316.3.3 Channel-Width Dependence 37516.3.4 Dual-Gate Structure 37816.4 Reliability 37916.5 Summary 381Acknowledgments 381References 38217 Oxide Circuits for Flexible Electronics 383Kris Myny, Nikolaos Papadopoulos, Florian De Roose, and Paul Heremans17.1 Introduction 38317.2 Technology-Aware Design Considerations 38317.2.1 Etch-Stop Layer, Backchannel Etch, and Self-Aligned Transistors 38417.2.1.1 Etch-Stop Layer 38417.2.1.2 Backchannel Etch 38517.2.1.3 Self-Aligned Transistors 38517.2.1.4 Comparison 38617.2.2 Dual-Gate Transistors 38617.2.2.1 Stack Architecture 38617.2.2.2 Effect of the Backgate 38817.2.3 Moore’s Law for TFT Technologies 38917.2.3.1 Cmos 38917.2.3.2 Thin-Film Electronics Historically 38917.2.3.3 New Drivers for Thin-Film Scaling: Circuits 39017.2.3.4 L-Scaling 39117.2.3.5 W and L Scaling 39117.2.3.6 Overall Lateral Scaling 39117.2.3.7 Oxide Thickness and Supply Voltage Scaling 39117.2.4 Conclusion 39217.3 Digital Electronics 39217.3.1 Communication Chips 39217.3.2 Complex Metal-Oxide-Based Digital Chips 39517.4 Analog Electronics 39617.4.1 Thin-Film ADC Topologies 39617.4.2 Imager Readout Peripherals 39717.4.3 Healthcare Patches 39917.5 Summary 400Acknowledgments 400References 400Part VI Display and Memory Applications 40518 Oxide TFT Technology for Printed Electronics 407Toshiaki Arai18.1 OLEDs 40718.1.1 OLED Displays 40718.1.2 Organic Light-Emitting Diodes 40818.1.3 Printed OLEDs 40918.2 TFTs for OLED Driving 41318.2.1 TFT Candidates 41318.2.2 Pixel Circuits 41318.2.3 Oxide TFTs 41418.2.3.1 Bottom-Gate TFTs 41518.2.3.2 Top-Gate TFTs 41818.3 Oxide TFT–Driven Printed OLED Displays 42418.4 Summary 427References 42819 Mechanically Flexible Nonvolatile Memory Thin-Film Transistors Using Oxide Semiconductor Active Channels on Ultrathin Polyimide Films 431Sung-Min Yoon, Hyeong-Rae Kim, Hye-Won Jang, Ji-Hee Yang, Hyo-Eun Kim, and Sol-Mi Kwak19.1 Introduction 43119.2 Fabrication of Memory TFTs 43219.2.1 Substrate Preparation 43219.2.2 Device Fabrication Procedures 43419.2.3 Characterization Methodologies 43519.3 Device Operations of Flexible Memory TFTs 43719.3.1 Optimization of Flexible IGZO-TFTs on PI Films 43719.3.2 Nonvolatile Memory Operations of Flexible Memory TFTs 43819.3.3 Operation Mechanisms and Device Physics 44219.4 Choice of Alternative Materials 44419.4.1 Introduction to Conducting Polymer Electrodes 44419.4.2 Introduction of Polymeric Gate Insulators 44619.5 Device Scaling to Vertical-Channel Structures 44719.5.1 Vertical-Channel IGZO-TFTs on PI Films 44719.5.2 Vertical-Channel Memory TFTs Using IGZO Channel and ZnO Trap Layers 44919.6 Summary 45319.6.1 Remaining Technical Issues 45319.6.2 Conclusions and Outlooks 453References 45420 Amorphous Oxide Semiconductor TFTs for BEOL Transistor Applications 457Nobuyoshi Saito and Keiji Ikeda20.1 Introduction 45720.2 Improvement of Immunity to H 2 Annealing 45820.3 Increase of Mobility and Reduction of S/D Parasitic Resistance 46320.4 Demonstration of Extremely Low Off-State Leakage Current Characteristics 467References 47121 Ferroelectric-HfO 2 Transistor Memory with IGZO Channels 473Masaharu Kobayashi21.1 Introduction 47321.2 Device Operation and Design 47521.3 Device Fabrication 47821.4 Experimental Results and Discussions 47921.4.1 FE-HfO 2 Capacitors with an IGZO Layer 47921.4.2 IGZO Channel FeFETs 48121.5 Summary 484Acknowledgments 484References 48522 Neuromorphic Chips Using AOS Thin-Film Devices 487Mutsumi Kimura22.1 Introduction 48722.2 Neuromorphic Systems with Crosspoint-Type α-GTO Thin-Film Devices 48822.2.1 Neuromorphic Systems 48822.2.1.1 α-GTO Thin-Film Devices 48822.2.1.2 System Architecture 48922.2.2 Experimental Results 49222.3 Neuromorphic System Using an LSI Chip and α-IGZO Thin-Film Devices [24] 49322.3.1 Neuromorphic System 49422.3.1.1 Neuron Elements 49422.3.1.2 Synapse Elements 49422.3.1.3 System Architecture 49522.3.2 Working Principle 49522.3.2.1 Cellular Neural Network 49522.3.2.2 Tug-of-War Method 49722.3.2.3 Modified Hebbian Learning 49722.3.2.4 Majority-Rule Handling 49822.3.3 Experimental Results 49822.3.3.1 Raw Data 49822.3.3.2 Associative Memory 49922.4 Conclusion 499Acknowledgments 500References 50023 Oxide TFTs and Their Application to X-Ray Imaging 503Robert A. Street23.1 Introduction 50323.2 Digital X-Ray Detection and Imaging Modalities 50423.2.1 Indirect Detection Imaging 50423.2.2 Direct Detection Imaging 50523.2.3 X-Ray Imaging Modalities 50523.3 Oxide-TFT X-Ray Detectors 50623.3.1 TFT Backplane Requirements for Digital X-Rays 50623.3.2 An IGZO Detector Fabrication and Characterization 50623.3.3 Other Reported Oxide X-Ray Detectors 50923.4 How Oxide TFTs Can Improve Digital X-Ray Detectors 50923.4.1 Noise and Image Quality in X-Ray Detectors 51023.4.2 Minimizing Additive Electronic Noise with Oxides 51023.4.3 Pixel Amplifier Backplanes 51123.4.4 IGZO-TFT Noise 51123.5 Radiation Hardness of Oxide TFTs 51323.6 Oxide Direct Detector Materials 51523.7 Summary 515References 515Part VII New Materials 51924 Toward the Development of High-Performance p-Channel Oxide-TFTs and All-Oxide Complementary Circuits 521Kenji Nomura24.1 Introduction 52124.2 Why Is High-Performance p-Channel Oxide Difficult? 52124.3 The Current Development of p-Channel Oxide-TFTs 52424.4 Comparisons of p-Type Cu 2 O and SnO Channels 52624.5 Comparisons of the TFT Characteristics of Cu 2 O and SnO-TFTs 52924.6 Subgap Defect Termination for p-Channel Oxides 53224.7 All-Oxide Complementary Circuits 53424.8 Conclusions 535References 53625 Solution-Synthesized Metal Oxides and Halides for Transparent p-Channel TFTs 539Ao Liu, Huihui Zhu, and Yong-Young Noh25.1 Introduction 53925.2 Solution-Processed p-Channel Metal-Oxide TFTs 54025.3 Transparent Copper(I) Iodide (CuI)–Based TFTs 54625.4 Conclusions and Perspectives 548Acknowledgments 549References 54926 Tungsten-Doped Active Layers for High-Mobility AOS-TFTs 553Zhang Qun26.1 Introduction 55326.2 Advances in Tungsten-Doped High-Mobility AOS-TFTs 55526.2.1 a-IWO-TFTs 55526.2.2 a-IZWO-TFTs 56226.2.3 Dual Tungsten-Doped Active-Layer TFTs 56526.2.4 Treatment on the Backchannel Surface 56626.3 Perspectives for High-Mobility AOS Active Layers 570References 57227 Rare Earth– and Transition Metal–Doped Amorphous Oxide Semiconductor Phosphors for Novel Light-Emitting Diode Displays 577Keisuke Ide, Junghwan Kim, Hideo Hosono, and Toshio Kamiya27.1 Introduction 57727.2 Eu-Doped Amorphous Oxide Semiconductor Phosphor 57727.3 Multiple-Color Emissions from Various Rare Earth–Doped AOS Phosphors 57927.4 Transition Metal–Doped AOS Phosphors 582References 58428 Application of AOSs to Charge Transport Layers in Electroluminescent Devices 585Junghwan Kim and Hideo Hosono28.1 Electronic Structure and Electrical Properties of Amorphous Oxide Semiconductors (AOSs) 58528.2 Criteria for Charge Transport Layers in Electroluminescent (EL) Devices 58528.3 Amorphous Zn-Si-O Electron Transport Layers for Perovskite Light-Emitting Diodes (PeLEDs) 58728.4 Amorphous In-Mo-O Hole Injection Layers for OLEDs 58928.5 Perspective 594References 59529 Displays and Vertical-Cavity Surface-Emitting Lasers 597Kenichi Iga29.1 Introduction to Displays 59729.2 Liquid Crystal Displays (LCDs) 59729.2.1 History of LCDs 59729.2.2 Principle of LCD: The TN Mode 59829.2.3 Other LC Modes 60029.2.4 Light Sources 60029.2.5 Diffusion Plate and Light Guiding Layer 60129.2.6 Microlens Arrays 60129.2.7 Short-Focal-Length Projection 60229.3 Organic EL Display 60229.3.1 Method (a): Color-Coding Method 60329.3.2 Method (b): Filter Method 60329.3.3 Method (c): Blue Conversion Method 60329.4 Vertical-Cavity Surface-Emitting Lasers 60429.4.1 Motivation of Invention 60429.4.2 What Is the Difference? 60529.4.3 Device Realization 60529.4.4 Applications 60729.5 Laser Displays including VCSELs 60729.5.1 Laser Displays 60729.5.2 Color Gamut 60829.5.3 Laser Backlight Method 609Acknowledgments 610References 611Index 613