Ba(Bi,Na)TiSnO₃ 세라믹스의 DC-바이어스 신뢰성 향상과 고온 유전 안정성 연구 = Enhanced DC-Bias Reliability and High-Temperature Dielectric Stability of Ba(Bi,Na)TiSnO₃ Ceramics

다국어 초록 (Multilingual Abstract)

As the demand for electronic devices operating in high-temperature environments increases, research on lead-free dielectric ceramics that satisfy both stable dielectric properties and high reliability is being actively conducted. In particular, Multi-Layer Ceramic Capacitors (MLCCs) are subjected to DC-bias electric fields alongside AC signals in practical operating conditions, which can lead to performance degradation such as reduced permittivity and increased dielectric loss. These issues become more pronounced under high-temperature conditions; thus, securing stable dielectric properties under simultaneous high-temperature and DC-bias conditions is recognized as a critical challenge in the development of dielectric materials for MLCCs.
In this study, a dual-site engineering strategy that simultaneously controls the A-site and B-site was proposed to enhance the high-temperature dielectric stability and DC-bias reliability of BaTiO3-based lead-free dielectric ceramics. To this end, (Ba1-x(Bi0.5Na0.5)x)(Ti0.9Sn0.1)O3(BBN-TS) ceramics were synthesized, and the effects of Bi3+/Na+ A-site substitution and Sn4+ B-site substitution on the crystal structure, microstructure, and dielectric properties were systematically analyzed. X-ray diffraction (XRD) analysis confirmed the formation of a pseudocubic perovskite structure at compositions of x ≥ 0.2, with lattice contraction and promoted grain growth observed as the substitution amount increased.
Dielectric property analysis revealed that the Bi3+/Na+ and Sn4+ substitutions induced relaxor ferroelectric behavior, effectively suppressing dielectric loss while broadening the permittivity peak. Specifically, the x = 0.8 composition maintained a high permittivity of approximately 3,000 and exhibited excellent dielectric stability over a wide temperature range of 67– 332 °C. Impedance spectroscopy confirmed that the electrical conduction behavior is predominantly governed by grain boundaries, and the Schottky barrier height increased with higher substitution levels, contributing to the reduction of dielectric loss in high-temperature regions. Furthermore, the Sn substitution significantly stabilized the dielectric properties under DC-bias and effectively suppressed thermal hysteresis.
These results suggest that the synergistic substitution of Bi3+/Na+ and 10 mol% Sn4+ alleviates the excessive structural anisotropy in the BT–BNT based system and stabilizes the relaxor phase, thereby ensuring superior dielectric performance even under high-temperature and DC-bias conditions. This study presents a new direction for designing high-reliability lead-free dielectric ceramics through dual-site engineering and suggests their potential for next-generation high-temperature MLCC applications. Key words : Temperature stability, DC-bias, lead-free, relaxor, dielectric.

목차 (Table of Contents)

• 제 1 장 서론 1
• 제 2 장 이론적 배경 4
• 2.1. 고온용 MLCC의 요구사항과 DC-bias 효과 4
• 2.1.1. Multi Layer Ceramic Capacitor(MLCC) 5
• 2.1.2. 현재 MLCC의 작동 환경 8
• 2.1.3. 유전 특성의 온도 의존성 저하 10
• 2.1.4. DC-bias 효과 13
• 2.2. BaTiO3 기반 무연 유전 세라믹 15
• 2.2.1. BaTiO3의 결정구조와 강유전성 16
• 2.2.2. BaTiO3 기반 세라믹의 이점 19
• 2.2.3. 고온과 DC-bias 하에서의 한계 21
• 2.3. BaTiO3 기반 시스템에서 A-site 치환(Bi/Na) 23
• 2.4. Relaxor ferroelectrics와 Polar nano-regions 26
• 2.5. BaTiO3 기반 시스템에서 B-site 치환(Sn) 28
• 2.6. Dual site engineering 이론 30
• 2.7. Grain boundary 전도와 Schottky barrier model 31
• 제 3 장 실험방법 및 특성평가 32
• 3.1. 실험방법 32
• 3.1.1. 분말합성 32
• 3.1.2. 분말소결 33
• 3.2. 특성평가 35
• 3.2.1. X-선 회절분석 35
• 3.2.2. 미세구조 분석 36
• 3.2.3. 유전 특성 분석 37
• 3.2.3.1. 온도에 따른 유전 특성 분석 37
• 3.2.3.2. 고온에서 유전 특성의 안정성 분석 38
• 3.2.4. 전기적 특성 분석 39
• 3.2.5. DC bias 특성 비교 분석 40
• 제 4 장 실험결과 및 고찰 41
• 4.1. (Ba1-x(Bi0.5Na0.5)x)(Ti0.9Sn0.1)O3 세라믹의 구조적 특성 41
• 4.1.1. X-선 회절 분석(XRD) & 리트벨트 정량 분석 41
• 4.1.2. 미세구조 분석 46
• 4.2. (Ba1-x(Bi0.5Na0.5)x)(Ti0.9Sn0.1)O3 세라믹의 유전특성 49
• 4.2.1. 온도에 따른 유전 특성 분석 49
• 4.2.2. 고온 유전 안정성 평가 53
• 4.3. (Ba1-x(Bi0.5Na0.5)x)(Ti0.9Sn0.1)O3 세라믹의 전기적 특성 59
• 4.4. Sn 안정화 유무에 따른 특성 비교 분석 65
• 4.4.1 Sn 안정화 유무에 따른 DC bias 특성 분석 65
• 4.4.2 Sn 안정화 유무에 따른 Thermal hysteresis 특성 분석 68
• 제 5 장 결론 72