Amorphous Oxide Semiconductors: IGZO and Related Materials for Display and Memory

Cover
Title Page
Copyright
Contents
Preface
Series Editor's Foreword
About the Editors
List of Contributors
Part I Introduction
Chapter 1.1 Transparent Amorphous Oxide Semiconductors for Display Applications
1.1.1 Introduction to Amorphous Semiconductors as Thin‐Film Transistor (TFT) Channels
1.1.2 Historical Overview
1.1.3 Oxide and Silicon
1.1.4 Transparent Amorphous Oxide Semiconductors
1.1.4.1 Electronic Structures
1.1.4.2 Materials
1.1.4.3 Characteristic Carrier Transport Properties
1.1.4.4 Electronic States
1.1.5 P‐Type Oxide Semiconductors for Display Applications
1.1.5.1 Oxides of Transition Metal Cations with an Electronic Configuration of (n−1)d10ns0 (n = 4 or 5)
1.1.5.2 Oxides of Metal Cations with an Electronic Configuration of ns2
1.1.5.3 Oxides of Metal Cations with an Electronic Configuration of nd6
1.1.6 Novel Amorphous Oxide Semiconductors
1.1.7 Summary and Outlook
References
Chapter 1.2 Transparent Amorphous Oxide Semiconductors
1.2.1 Introduction
1.2.2 Technical Issues and Requirements of TFTs for AM‐FPDs
1.2.2.1 Field‐Effect Mobility
1.2.2.2 Off‐State Leakage Current and On/Off Current Ratio
1.2.2.3 Stability and Reliability
1.2.2.4 Uniformity
1.2.2.5 Large‐Area Devices by Large‐Area Mother‐Glass Substrates
1.2.2.6 Low‐Temperature Fabrication and Flexibility
1.2.3 History, Features, Uniqueness, Development, and Applications of AOS‐TFTs
1.2.3.1 History
1.2.3.2 Features and Uniqueness
1.2.3.3 Applications
1.2.3.4 Development and Products of AM‐FPDs
1.2.4 Summary
References
Part II Fundamentals
Chapter 2 Electronic Structure and Structural Randomness
2.1 Introduction
2.2 Brief Description of Methods and Approaches
2.2.1 Computational Approach
2.2.2 Experimental Approach
2.3 The Structure and Properties of Crystalline and Amorphous In2O3
2.4 The Structure and Properties of Crystalline and Amorphous SnO2
2.5 The Structure and Properties of Crystalline and Amorphous ZnO
2.6 The Structure and Properties of Crystalline and Amorphous Ga2O3
2.7 Role of Morphology in Structure–Property Relationships
2.8 The Role of Composition in Structure–Property Relationships: IGO and IGZO
2.9 Conclusions
References
Chapter 3 Electronic Structure of Transparent Amorphous Oxide Semiconductors
3.1 Introduction
3.2 Mobility
3.3 Density of States
3.4 Band Structures of n‐Type Semiconductors
3.5 Instabilities
3.6 Doping Limits and Finding Effective Oxide Semiconductors
3.7 OLED Electrodes
3.8 Summary
References
Chapter 4 Defects and Relevant Properties
4.1 Introduction
4.2 Typical Deposition Condition
4.3 Overview of Electronic Defects in AOSs
4.4 Origins of Electron Donors
4.5 Oxygen‐ and Hydrogen‐Related Defects and Near‐VBM States
4.6 Summary
References
Chapter 5 Amorphous Semiconductor Mobility Physics and TFT Modeling
5.1 Amorphous Semiconductor Mobility: An Introduction
5.2 Diffusive Mobility
5.3 Density of States
5.4 TFT Mobility Considerations
5.5 TFT Mobility Extraction, Fitting, and Model Validation
5.6 Physics‐Based TFT Mobility Modeling
5.7 Conclusions
References
Chapter 6 Percolation Description of Charge Transport in Amorphous Oxide Semiconductors: Band Conduction Dominated by Disorder
6.1 Introduction
6.2 Band Transport via Extended States in the Random‐Barrier Model (RBM)
6.2.1 Deficiencies of the Rate‐Averaging Approach: Electrotechnical Analogy
6.2.2 Percolation Approach to Charge Transport in the RBM
6.3 Random Band‐Edge Model (RBEM) for Charge Transport in AOSs
6.4 Percolation Theory for Charge Transport in the RBEM
6.4.1 From Regional to Global Conductivities in Continuum Percolation Theory
6.4.2 Averaging Procedure by Adler et al.
6.5 Comparison between Percolation Theory and EMA
6.6 Comparison with Experimental Data
6.7 Discussion and Conclusions
6.7.1 Textbook Description of Charge Transport in Traditional Crystalline Semiconductors (TCSs)
6.7.2 Results of This Chapter for Charge Transport in Amorphous Oxide Semiconductors (AOSs)
6.7.2 Acknowledgments
References
Chapter 7 State and Role of Hydrogen in Amorphous Oxide Semiconductors
7.1 Introduction
7.2 Concentration and Chemical States
7.3 Carrier Generation and Hydrogen
7.3.1 Carrier Generation by H Injection at Low Temperatures
7.3.2 Carrier Generation and Annihilation by Thermal Treatment
7.4 Energy Levels and Electrical Properties
7.5 Incorporation and Conversion of H Impurities
7.6 Concluding Remarks
Acknowledgments
References
Part III Processing
Chapter 8 Low‐Temperature Thin‐Film Combustion Synthesis of Metal‐Oxide Semiconductors: Science and Technology
8.1 Introduction
8.2 Low‐Temperature Solution‐Processing Methodologies
8.2.1 Alkoxide Precursors
8.2.2 Microwave‐Assisted Annealing
8.2.3 High‐Pressure Annealing
8.2.4 Photonic Annealing
8.2.4.1 Laser Annealing
8.2.4.2 Deep‐Ultraviolet Illumination
8.2.4.3 Flash Lamp Annealing
8.2.5 Redox Reactions
8.3 Combustion Synthesis for MO TFTs
8.3.1 n‐Type MO TFTs
8.3.2 p‐Type MO TFTs
8.4 Summary and Perspectives
Acknowledgments
References
Chapter 9 Solution‐Processed Metal‐Oxide Thin‐Film Transistors for Flexible Electronics
9.1 Introduction
9.2 Fundamentals of Solution‐Processed Metal‐Oxide Thin‐Film Transistors
9.2.1 Deposition Methods for Solution‐Processed Oxide Semiconductors
9.2.1.1 Coating‐Based Deposition Methods
9.2.1.2 Printing‐Based Deposition Methods
9.2.2 The Formation Mechanism of Solution‐Processed Oxide Semiconductor Films
9.3 Low‐Temperature Technologies for Active‐Layer Engineering of Solution‐Processed Oxide TFTs
9.3.1 Overview
9.3.2 Solution Modulation
9.3.2.1 Alkoxide Precursors
9.3.2.2 pH Adjustment
9.3.2.3 Combustion Reactions
9.3.2.4 Aqueous Solvent
9.3.3 Process Modulation
9.3.3.1 Photoactivation Process
9.3.3.2 High‐Pressure Annealing (HPA) Process
9.3.3.3 Microwave‐Assisted Annealing Process
9.3.3.4 Plasma‐Assisted Annealing Process
9.3.4 Structure Modulation
9.3.4.1 Homojunction Dual‐Active or Multiactive Layer
9.3.4.2 Heterojunction Dual‐ or Multiactive Layer
9.4 Applications of Flexible Electronics with Low‐Temperature Solution‐Processed Oxide TFTs
9.4.1 Flexible Displays
9.4.2 Flexible Sensors
9.4.3 Flexible Integrated Circuits
References
Chapter 10 Recent Progress on Amorphous Oxide Semiconductor Thin‐Film Transistors Using the Atomic Layer Deposition Technique
10.1 Atomic Layer Deposition (ALD) for Amorphous Oxide Semiconductor (AOS) Applications
10.1.1 The ALD Technique
10.1.2 Research Motivation for ALD AOS Applications
10.2 AOS‐TFTs Based on ALD
10.2.1 Binary Oxide Semiconductor TFTs Based on ALD
10.2.1.1 ZnO‐TFTs
10.2.1.2 InOx‐TFTs
10.2.1.3 SnOx‐TFTs
10.2.2 Ternary and Quaternary Oxide Semiconductor TFTs Based on ALD
10.2.2.1 Indium–Zinc Oxide (IZO) and Indium–Gallium Oxide (IGO)
10.2.2.2 Zinc–Tin Oxide (ZTO)
10.2.2.3 Indium–Gallium–Zinc Oxide (IGZO)
10.2.2.4 Indium–Tin–Zinc Oxide (ITZO)
10.3 Challenging Issues of AOS Applications Using ALD
10.3.1 p‐Type Oxide Semiconductors
10.3.1.1 Tin Monoxide (SnO)
10.3.1.2 Copper Oxide (CuxO)
10.3.2 Enhancing Device Performance: Mobility and Stability
10.3.2.1 Composition Gradient Oxide Semiconductors
10.3.2.2 Two‐Dimensional Electron Gas (2DEG) Oxide Semiconductors
10.3.2.3 Spatial and Atmospheric ALD for Oxide Semiconductors
References
Part IV Thin‐Film Transistors
Chapter 11 Control of Carrier Concentrations in AOSs and Application to Bulk‐Accumulation TFTs
11.1 Introduction
11.2 Control of Carrier Concentration in a‐IGZO
11.3 Effect of Carrier Concentration on the Performance of a‐IGZO TFTs with a Dual‐Gate Structure
11.3.1 Inverted Staggered TFTs
11.3.2 Coplanar TFTs
11.4 High‐Drain‐Current, Dual‐Gate Oxide TFTs
11.5 Stability of Oxide TFTs: PBTS, NBIS, HCTS, Hysteresis, and Mechanical Strain
11.6 TFT Circuits: Ring Oscillators and Amplifier Circuits
11.7 Conclusion
References
Chapter 12 Elevated‐Metal Metal‐Oxide Thin‐Film Transistors: A Back‐Gate Transistor Architecture with Annealing‐Induced Source/Drain Regions
12.1 Introduction
12.1.1 Semiconducting Materials for a TFT
12.1.1.1 Amorphous Silicon
12.1.1.2 Low‐Temperature Polycrystalline Silicon
12.1.1.3 MO Semiconductors
12.1.2 TFT Architectures
12.2 Annealing‐Induced Generation of Donor Defects
12.2.1 Effects of Annealing on the Resistivity of IGZO
12.2.2 Microanalyses of the Thermally Annealed Samples
12.2.3 Lateral Migration of the Annealing‐Induced Donor Defects
12.3 Elevated‐Metal Metal‐Oxide (EMMO) TFT Technology
12.3.1 Technology and Characteristics of IGZO EMMO TFTs
12.3.2 Applicability of EMMO Technology to Other MO Materials
12.3.3 Fluorinated EMMO TFTs
12.3.4 Resilience of Fluorinated MO against Hydrogen Doping
12.3.5 Technology and Display Resolution Trend
12.4 Enhanced EMMO TFT Technologies
12.4.1 3‐EMMO TFT Technology
12.4.2 Self‐Aligned EMMO TFTs
12.5 Conclusion
Acknowledgments
References
Chapter 13 Hot Carrier Effects in Oxide‐TFTs
13.1 Introduction
13.2 Analysis of Hot Carrier Effect in IGZO‐TFTs
13.2.1 Photoemission from IGZO‐TFTs
13.2.2 Kink Current in Photon Emission Condition
13.2.3 Hot Carrier–Induced Degradation of a‐IGZO‐TFTs
13.3 Analysis of the Hot Carrier Effect in High‐Mobility Oxide‐TFTs
13.3.1 Bias Stability under DC Stresses in a High‐Mobility IWZO‐TFT
13.3.2 Analysis of Dynamic Stress in Oxide‐TFTs
13.3.3 Photon Emission from the IWZO‐TFT under Pulse Stress
13.4 Conclusion
References
Chapter 14 Carbon‐Related Impurities and NBS Instability in AOS‐TFTs
14.1 Introduction
14.2 Experimental
14.3 Results and Discussion
14.4 Summary
References
Part V TFTs and Circuits
Chapter 15 Oxide TFTs for Advanced Signal‐Processing Architectures
15.1 Introduction
15.1.1 Device–Circuit Interactions
15.2 Above‐Threshold TFT Operation and Defect Compensation: AMOLED Displays
15.2.1 AMOLED Display Challenges
15.2.2 Above‐Threshold Operation
15.2.3 Temperature Dependence
15.2.4 Effects of Process‐Induced Spatial Nonuniformity
15.2.5 Overview of External Compensation for AMOLED Displays
15.3 Ultralow‐Power TFT Operation in a Deep Subthreshold (Near Off‐State) Regime
15.3.1 Schottky Barrier TFTs
15.3.2 Device Characteristics and Small Signal Parameters
15.3.3 Common Source Amplifier
15.4 Oxide TFT‐Based Image Sensors
15.4.1 Heterojunction Oxide Photo‐TFTs
15.4.2 Persistent Photocurrent
15.4.3 All‐Oxide Photosensor Array
References
Chapter 16 Device Modeling and Simulation of TAOS‐TFTs
16.1 Introduction
16.2 Device Models for TAOS‐TFTs
16.2.1 Mobility Model
16.2.2 Density of Subgap States (DOS) Model
16.2.3 Self‐Heating Model
16.3 Applications
16.3.1 Temperature Dependence
16.3.2 Channel‐Length Dependence
16.3.3 Channel‐Width Dependence
16.3.4 Dual‐Gate Structure
16.4 Reliability
16.5 Summary
Acknowledgments
References
Chapter 17 Oxide Circuits for Flexible Electronics
17.1 Introduction
17.2 Technology‐Aware Design Considerations
17.2.1 Etch‐Stop Layer, Backchannel Etch, and Self‐Aligned Transistors
17.2.1.1 Etch‐Stop Layer
17.2.1.2 Backchannel Etch
17.2.1.3 Self‐Aligned Transistors
17.2.1.4 Comparison
17.2.2 Dual‐Gate Transistors
17.2.2.1 Stack Architecture
17.2.2.2 Effect of the Backgate
17.2.3 Moore's Law for TFT Technologies
17.2.3.1 CMOS
17.2.3.2 Thin‐Film Electronics Historically
17.2.3.3 New Drivers for Thin‐Film Scaling: Circuits
17.2.3.4 L‐Scaling
17.2.3.5 W and L Scaling
17.2.3.6 Overall Lateral Scaling
17.2.3.7 Oxide Thickness and Supply Voltage Scaling
17.2.4 Conclusion
17.3 Digital Electronics
17.3.1 Communication Chips
17.3.2 Complex Metal‐Oxide‐Based Digital Chips
17.4 Analog Electronics
17.4.1 Thin‐Film ADC Topologies
17.4.2 Imager Readout Peripherals
17.4.3 Healthcare Patches
17.5 Summary
Acknowledgments
References
Part VI Display and Memory Applications
Chapter 18 Oxide TFT Technology for Printed Electronics
18.1 OLEDs
18.1.1 OLED Displays
18.1.2 Organic Light‐Emitting Diodes
18.1.3 Printed OLEDs
18.2 TFTs for OLED Driving
18.2.1 TFT Candidates
18.2.2 Pixel Circuits
18.2.3 Oxide TFTs
18.2.3.1 Bottom‐Gate TFTs
18.2.3.2 Top‐Gate TFTs
18.3 Oxide TFT–Driven Printed OLED Displays
18.4 Summary
References
Chapter 19 Mechanically Flexible Nonvolatile Memory Thin‐Film Transistors Using Oxide Semiconductor Active Channels on Ultrathin Polyimide Films
19.1 Introduction
19.2 Fabrication of Memory TFTs
19.2.1 Substrate Preparation
19.2.2 Device Fabrication Procedures
19.2.3 Characterization Methodologies
19.3 Device Operations of Flexible Memory TFTs
19.3.1 Optimization of Flexible IGZO‐TFTs on PI Films
19.3.2 Nonvolatile Memory Operations of Flexible Memory TFTs
19.3.3 Operation Mechanisms and Device Physics
19.4 Choice of Alternative Materials
19.4.1 Introduction to Conducting Polymer Electrodes
19.4.2 Introduction of Polymeric Gate Insulators
19.5 Device Scaling to Vertical‐Channel Structures
19.5.1 Vertical‐Channel IGZO‐TFTs on PI Films
19.5.2 Vertical‐Channel Memory TFTs Using IGZO Channel and ZnO Trap Layers
19.6 Summary
19.6.1 Remaining Technical Issues
19.6.2 Conclusions and Outlooks
References
Chapter 20 Amorphous Oxide Semiconductor TFTs for BEOL Transistor Applications
20.1 Introduction
20.2 Improvement of Immunity to H2 Annealing
20.3 Increase of Mobility and Reduction of S/D Parasitic Resistance
20.4 Demonstration of Extremely Low Off‐State Leakage Current Characteristics
References
Chapter 21 Ferroelectric‐HfO2 Transistor Memory with IGZO Channels
21.1 Introduction
21.2 Device Operation and Design
21.3 Device Fabrication
21.4 Experimental Results and Discussions
21.4.1 FE‐HfO2 Capacitors with an IGZO Layer
21.4.2 IGZO Channel FeFETs
21.5 Summary
Acknowledgments
References
Chapter 22 Neuromorphic Chips Using AOS Thin‐Film Devices
22.1 Introduction
22.2 Neuromorphic Systems with Crosspoint‐Type α‐GTO Thin‐Film Devices
22.2.1 Neuromorphic Systems
22.2.1.1 α‐GTO Thin‐Film Devices
22.2.1.2 System Architecture
22.2.2 Experimental Results
22.3 Neuromorphic System Using an LSI Chip and α‐IGZO Thin‐Film Devices
22.3.1 Neuromorphic System
22.3.1.1 Neuron Elements
22.3.1.2 Synapse Elements
22.3.1.3 System Architecture
22.3.2 Working Principle
22.3.2.1 Cellular Neural Network
22.3.2.2 Tug‐of‐War Method
22.3.2.3 Modified Hebbian Learning
22.3.2.4 Majority‐Rule Handling
22.3.3 Experimental Results
22.3.3.1 Raw Data
22.3.3.2 Associative Memory
22.4 Conclusion
Acknowledgments
References
Chapter 23 Oxide TFTs and Their Application to X‐Ray Imaging
23.1 Introduction
23.2 Digital X‐Ray Detection and Imaging Modalities
23.2.1 Indirect Detection Imaging
23.2.2 Direct Detection Imaging
23.2.3 X‐Ray Imaging Modalities
23.3 Oxide‐TFT X‐Ray Detectors
23.3.1 TFT Backplane Requirements for Digital X‐Rays
23.3.2 An IGZO Detector Fabrication and Characterization
23.3.3 Other Reported Oxide X‐Ray Detectors
23.4 How Oxide TFTs Can Improve Digital X‐Ray Detectors
23.4.1 Noise and Image Quality in X‐Ray Detectors
23.4.2 Minimizing Additive Electronic Noise with Oxides
23.4.3 Pixel Amplifier Backplanes
23.4.4 IGZO‐TFT Noise
23.5 Radiation Hardness of Oxide TFTs
23.6 Oxide Direct Detector Materials
23.7 Summary
References
Part VII New Materials
Chapter 24 Toward the Development of High‐Performance p‐Channel Oxide‐TFTs and All‐Oxide Complementary Circuits
24.1 Introduction
24.2 Why Is High‐Performance p‐Channel Oxide Difficult?
24.3 The Current Development of p‐Channel Oxide‐TFTs
24.4 Comparisons of p‐Type Cu2O and SnO Channels
24.5 Comparisons of the TFT Characteristics of Cu2O and SnO‐TFTs
24.6 Subgap Defect Termination for p‐Channel Oxides
24.7 All‐Oxide Complementary Circuits
24.8 Conclusions
References
Chapter 25 Solution‐Synthesized Metal Oxides and Halides for Transparent p‐Channel TFTs
25.1 Introduction
25.2 Solution‐Processed p‐Channel Metal‐Oxide TFTs
25.3 Transparent Copper(I) Iodide (CuI)–Based TFTs
25.4 Conclusions and Perspectives
Acknowledgments
References
Chapter 26 Tungsten‐Doped Active Layers for High‐Mobility AOS‐TFTs
26.1 Introduction
26.2 Advances in Tungsten‐Doped High‐Mobility AOS‐TFTs
26.2.1 a‐IWO‐TFTs
26.2.2 a‐IZWO‐TFTs
26.2.3 Dual Tungsten‐Doped Active‐Layer TFTs
26.2.4 Treatment on the Backchannel Surface
26.3 Perspectives for High‐Mobility AOS Active Layers
References
Chapter 27 Rare Earth– and Transition Metal–Doped Amorphous Oxide Semiconductor Phosphors for Novel Light‐Emitting Diode Displays
27.1 Introduction
27.2 Eu‐Doped Amorphous Oxide Semiconductor Phosphor
27.3 Multiple‐Color Emissions from Various Rare Earth–Doped AOS Phosphors
27.4 Transition Metal–Doped AOS Phosphors
References
Chapter 28 Application of AOSs to Charge Transport Layers in Electroluminescent Devices
28.1 Electronic Structure and Electrical Properties of Amorphous Oxide Semiconductors (AOSs)
28.2 Criteria for Charge Transport Layers in Electroluminescent (EL) Devices
28.3 Amorphous Zn‐Si‐O Electron Transport Layers for Perovskite Light‐Emitting Diodes (PeLEDs)
28.4 Amorphous In‐Mo‐O Hole Injection Layers for OLEDs
28.5 Perspective
References
Chapter 29 Displays and Vertical‐Cavity Surface‐Emitting Lasers
29.1 Introduction to Displays
29.2 Liquid Crystal Displays (LCDs)
29.2.1 History of LCDs
29.2.2 Principle of LCD: The TN Mode
29.2.3 Other LC Modes
29.2.4 Light Sources
29.2.5 Diffusion Plate and Light Guiding Layer
29.2.6 Microlens Arrays
29.2.7 Short‐Focal‐Length Projection
29.3 Organic EL Display
29.3.1 Method (a): Color‐Coding Method
29.3.2 Method (b): Filter Method
29.3.3 Method (c): Blue Conversion Method
29.4 Vertical‐Cavity Surface‐Emitting Lasers
29.4.1 Motivation of Invention
29.4.2 What Is the Difference?
29.4.3 Device Realization
29.4.4 Applications
29.5 Laser Displays including VCSELs
29.5.1 Laser Displays
29.5.2 Color Gamut
29.5.3 Laser Backlight Method
Acknowledgments
References
Index
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