This book explains the basic elements that readers need to know about amorphous silicon material and a-Si:H TFTs. It includes the main principles of the transistors operation, modeling and applications. Fundamentals about transport mechanisms in a-Si:H TFTs and the associated electronic properties are introduced and extended to design examples and strategies to build reliable, large-area, performance optimized circuits. The book also reviews the effect of the amorphous silicon nature and how it impacts the transistors properties and their relevant applications. Fundamentals are made as simple as possible to be easily grasped as they cover everything expected to be important for an easy understanding of the introduced concepts.
The author’s approach is geared toward undergraduate and graduate students, but the content is also appropriate for circuit simulator developers, integrated circuit designers and manufacturers, as well as everyone engaged in work on large area integrated circuit technologies and photovoltaics.
Author(s): Zoubeida Hafdi
Series: Synthesis Lectures on Engineering, Science, and Technology
Publisher: Springer
Year: 2023
Language: English
Pages: 140
City: Cham
Preface
Acknowledgements
Contents
Abbreviations
Symbols
1 Introduction
References
2 Hydrogenated Amorphous Silicon Thin-Film Transistors
2.1 Introduction
2.2 Amorphous Silicon and a-Si:H TFTs
2.3 Silicon Nitride
2.4 Thin-Film Transistor Structures
2.5 Thin-Film Transistor Materials
2.6 a-Si:H TFTs Performance Requirements
2.7 a-Si:H TFT Operation
2.7.1 Subthreshold or Weak Accumulation Regime
2.7.2 Above Threshold or High Accumulation Regime
2.7.3 Transitional Regime
2.7.4 Crystalline-Like Regime
References
3 Amorphous Silicon-Based MIS Structure
3.1 Introduction
3.2 Density of States in the Amorphous Silicon
3.3 Band Diagram
3.4 Charge Densities
3.4.1 Density of Free Electrons
3.4.2 Charge Density in the Deep Localized States
3.4.3 Charge Density in Tail Localized States
3.5 MIS Structure DC Analysis
3.5.1 Assumptions and Calculation Principle
3.5.2 Poisson Equation
3.5.3 Potential Equilibrium
3.6 Quantitative Study
3.6.1 Bulk Charge Density
3.6.2 Electrostatic Field and Electrostatic Potential
3.6.3 Induced Charge in the Semiconductor
3.6.4 Localized Charge
3.6.5 Free Electron Density
3.7 Profiles Analysis
3.7.1 Potential Profile
3.7.2 Charge Densities Profiles
3.8 Conclusion
References
4 Hydrogenated Amorphous Silicon Thin-Film Transistor: A DC Analysis
4.1 Introduction
4.2 Model Hypotheses
4.3 Drain Current
4.3.1 General Expression
4.3.2 Potential Equilibrium
4.4 Weak Accumulation Regime
4.4.1 Poisson Equation
4.4.2 Potential Equilibrium
4.4.3 Conduction Charge
4.4.4 Drain Current
4.4.5 Simplified Model
4.5 Strong Accumulation Regime
4.5.1 Poisson Equation
4.5.2 Potential Equilibrium
4.5.3 Conduction Charge
4.5.4 Drain Current
4.5.5 Simplified Model
4.6 Field Effect Mobility
4.6.1 Mobility Ratio in Weak Accumulation
4.6.2 Mobility Ratio in Strong Accumulation
4.7 Blocking State
4.8 Model Summary
4.8.1 Weak Accumulation (Vg < Vt)
4.8.2 Strong Accumulation (Vg ≥ Vt)
4.9 Model Parameters
4.10 Current–Voltage Characteristics
4.11 Threshold Voltage
4.12 On-to-Off Current Ratio
4.13 Field Effect Mobility-to-Band Mobility Ratio
4.14 Conclusion
References
5 Interface States in Amorphous Silicon Thin-Film Transistors
5.1 Introduction
5.2 Current–Voltage Characteristics
5.2.1 Lower Threshold Regime
5.2.2 Upper Threshold Regime
5.3 Field Effect Mobility
5.4 Subthreshold Swing
5.5 Surface States Impact
5.6 Conclusion
References
6 Hydrogenated Amorphous Silicon Thin-Film Transistor: A Dynamic Analysis
6.1 Introduction
6.2 Some Dynamic Model Aspects
6.3 Capacitance Model
6.3.1 Calculation of the Charges in Source and Drain Sides
6.3.2 Source Side Charge Calculation
6.3.3 Drain Side Charge Calculation
6.3.4 Total Charge Calculation
6.3.5 Intrinsic Gate-to-Source Capacitance Calculation
6.3.6 Intrinsic Gate-to-Drain Capacitance Calculation
6.4 Total Capacitances Analysis for Transistor Operational Regimes
6.4.1 Blocking State
6.4.2 Below Threshold Regime
6.4.3 Above Threshold Regime
6.5 Model Analysis
6.6 Conclusion
References
7 Amorphous Silicon Thin-Film Transistors for Digital Circuits
7.1 Introduction
7.2 a-Si-based Inverter
7.3 a-Si-based Logic Gates
7.4 a-Si:H TFT Model Implementation
7.5 Design Considerations for a-Si Logic Gates
7.6 Conclusion
References
8 Amorphous Silicon Thin-Film Transistors for Charge Pump Circuits
8.1 Introduction
8.2 The Dickson Charge Pump: Some Considerations
8.3 a-Si:H TFT-Based Charge Pump
8.4 Charge Pump Performance
8.4.1 Transient Regime
8.4.2 Steady-State Regime
8.5 Conclusion
References
