비정질 IGZO 박막 트랜지스터의 감마선 및 중성자 조사에 의한 트랩 거동 기반 신뢰성 분석 연구 = Trap-Centric Investigation of Gamma-Ray and Neutron-Induced Degradation in a-IGZO Thin-Film Transistors

다국어 초록 (Multilingual Abstract)

Amorphous In-Ga-Zn-O (a-IGZO) thin-film transistors (TFTs) are promising candidates for next-generation large-area electronics; however, ensuring their reliability under harsh radiation environments is essential for specialized applications. This thesis presents a systematic, trap-centric investigation into the radiation-induced degradation and recovery behaviors of a-IGZO TFTs, specifically comparing the effects of gamma-ray (γ-ray) total ionizing dose (TID) and neutron-induced displacement damage (DD). The devices were characterized before and after ⁶⁰Co γ-ray irradiation (total absorbed dose of 3,000 Gy) and ²⁵²Cf neutron irradiation (average energy of 2.2 MeV) using DC <i>I</i>–<i>V</i> measurements, subgap density of states (DOS) extraction, and low-frequency noise (LFN)-based trap quantification. Experimental results reveal that γ-ray irradiation induces a pronounced negative shift in threshold voltage (<i>V</i>_T) and degrades the subthreshold swing (<i>SS</i>), which is attributed to enhanced charge trapping near the gate-oxide/channel interface. Cross-sectional TEM analysis confirmed that this TID-dominant degradation occurs without discernible microstructural damage. In contrast, neutron irradiation results in transport-limited degradation, characterized by a significant increase in series resistance (<i>R</i>_SD) and a reduction in current drive, while the gate-oxide integrity remains largely unaffected.
To mitigate such degradation, this study proposes the use of a Ti metal capping layer combined with metal-capped electro-thermal annealing (MC-ETA). The MC-ETA process effectively restored the current drive and suppressed trap signatures through localized Joule heating, a mechanism further validated by electro-thermal COMSOL simulations. These findings clearly distinguish between TID- and DD-dominant behaviors and demonstrate a practical recovery strategy for the development of radiation-tolerant oxide TFTs.

목차 (Table of Contents)

• Table of Contents i
• List of Figures iii
• List of Tables vi
• Abstract vii
• 1. Introduction 9
• 2. Background 11
• 2.1 Thin-Film Transistors (TFTs) 11
• 2.2 Oxide Thin-Film Transistors 13
• 2.2.1 Indium Gallium Zinc Oxide (IGZO) 15
• 2.2.2 Defects and Subgap States in a-IGZO 17
• 2.3 Radiation Effects in Semiconductor Devices 19
• 2.3.1 Total Ionizing Dose (TID) Effects 19
• 2.3.2 Displacement Damage (DD) Effects 21
• 3. Experiments 23
• 3.1 Fabrication of a-IGZO TFTs 23
• 3.2 Fabrication of Metal-Capped a-IGZO TFTs 24
• 3.3 Irradiation and Measurement Setups 25
• 3.3.1 Gamma-ray Irradiation 25
• 3.3.2 Neutron Irradiation 26
• 3.3.3 Electrical Measurement Setups 27
• 4. Gamma-Ray Irradiation Effects on a-IGZO TFTs 28
• 4.1 DC I-V Characteristics 28
• 4.2 Positive Bias Stress (PBS) Validation 32
• 4.3 Low-Frequency Noise Characteristics 34
• 4.4 Oxide-Trap Extraction and Dielectric Degradation 36
• 4.5 Summary of Gamma-Ray Irradiation 38
• 5. Neutron Irradiation Effects on a-IGZO TFTs 39
• 5.1 DC I-V Characteristics 39
• 5.2 Defect States Evolution under Neutron Irradiation 41
• 5.3 Low-Frequency Noise Characteristics 43
• 6. Recovery Strategy for Neutron-Induced Degradation 45
• 6.1 DC I-V Recovery Method 45
• 6.2 Trap Recovery via MC-ETA 48
• 6.3 Electro-Thermal Analysis of the MC-ETA Process 50
• 6.4 Summary of Neutron-Induced Degradation and Recovery 51
• 7. Conclusion 52
• References 53
• Abstract (Korean) 60