Materials Engineering of ZnO based Amorphous Oxide Semiconductor Thin Film Transistors for Sensor and Logic Applications

다국어 초록 (Multilingual Abstract)

This research explores the development and characterization of advanced thin- film transistors (TFTs) for next-generation electronic applications such as sensors. The primary objective was to address the limitations of conventional gas and touch sensors by enhancing thermal stability, sensitivity, and electrical performance through innovative material engineering and structure-based device fabrication. Structural engineering of Si-Zn-Sn-O (SZTO) TFTs with metal capping layers demonstrated significant improvements in device performance, especially for touch sensor applications, by enhancing mobility and stability. The metal capping layers were introduced to SZTO TFTs, achieving a substantial increase in field-effect mobility from 20.7 cm²/V·s to 37.9 cm²/V·s by reducing channel resistance. Furthermore, the TFTs demonstrated excellent responsiveness to touch signals at low voltages (60 mV), highlighting their potential for next-generation touch sensor applications. In addition, material characterization and doping strategies were investigated, including Si-doped In–Zn–O (SIZO) TFTs for gas sensing applications and Ga-, Al-, and Hf-doped Zn–Sn–O (ZTO) TFTs. These studies demonstrate the crucial role of precise materials engineering in improving both sensitivity and robustness. ZTO- based AOSs were selected as indium-free alternatives to address economic and environmental concerns, while SIZO exhibited excellent performance even at low annealing temperatures, making it highly promising for flexible electronics. The TFTs were fabricated by RF magnetron sputtering, with metallic electrodes deposited via e-beam and thermal evaporation. Their electrical and physical properties were characterized using techniques such as X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV– Vis spectroscopy, and semiconductor parameter analysis (Agilent 4145). Furthermore, the use of a co-sputtering system to optimize TFT properties was explored to achieve enhanced performance. Overall, these findings emphasize the critical role of materials engineering in addressing challenges related to device performance and scalability, ensuring that these next-generation devices can meet the increasing demands of modern electronics.

목차 (Table of Contents)

• CHAPTER 1. Introduction 1
• CHAPTER 2. Background 4
• 2.1 History of amorphous oxide semiconductors 4
• 2.2 Introduction to thin film transistors 9
• 2.3 Theory of stress test and density of state 12
• 2.4 Application in logic circuits and sensor 15
• CHAPTER 3. Methodology 19
• 3.1 Design and methodology of AOS TFTs 19
• 3.1.1 Sputtering and evaporation methods 19
• 3.1.2 Investigation of AOS TFT materials 22
• 3.1.3 Fabrication process using the co-sputtering system 24
• 3.2 Fabrication process of AOS devices 27
• 3.2.1 Fabrication of Si-ZTO and IZO TFTs 27
• 3.2.2 Fabrication of XZTO (X=Ga,Al, and Hf) TFTs and TLMs 28
• 3.3 Fabrication of logic circuits and touch sensors 30
• CHAPTER 4. Result and discussion 33
• 4.1 Effect of MC sturucture on the characteristics of TFTs 33
• 4.2 Effect of Si ratio in a-SIZO TFTs 38
• 4.3 Effect of oxygen vacancy suppressor of a-ZTO TFTs 45
• 4.4 Effect of channel composition in co-sputtered TFTs 50
• 4.5 Applications of AOS TFTs· 56
• 4.5.1 Analysis of Logic circuits 56
• 4.1.2 Investigation on sensor applications 60
• CHAPTER 5. Conclusion 62
• References 63
• Acknowledgement 69
• 국문초록 71
• List of publications 73