W 형 육방정 페라이트-에폭시 몰딩 컴파운드 복합체의 전자기파 흡수 특성 연구 = A Study on Electromagnetic Wave Absorption Properties of W-type Hexaferrite-Epoxy Molding Compound Composites

다국어 초록 (Multilingual Abstract)

Recent advances in RF System-in-Package (SiP) technology have enabled highly integrated and miniaturized architectures to support multi-band and high-frequency operation. However, the increased integration density inevitably aggravates electromagnetic interference (EMI) issues inside the package, particularly in the Sub-6 GHz frequency range. Therefore, the development of thin and effective EMI suppression materials applicable to RF SiP environments has become increasingly important.
In this study, the applicability of W-type hexaferrite-based electromagnetic wave absorbers for mitigating EMI around 6 GHz in a 6 mm-class RF SiP environment was systematically investigated. BaZn2₋xCoxFe16O27 (x = 0.65, 0.70, 0.75) was employed as a reference system (System 1), and Sr-substituted Ba1₋xSrxZnCoFe16O27 (x = 0.75, 0.80, 0.85, 0.90) was introduced as a designed system (System 2) to examine the effects of compositional modification on magnetic and electromagnetic absorption properties.
All ferrite powders were synthesized via a solid-state reaction method and fabricated into ferrite–epoxy composite absorbers. X-ray diffraction analysis confirmed the formation of a single-phase W-type hexagonal structure for all compositions, while a systematic rightward shift of diffraction peaks was observed with increasing Sr substitution, indicating lattice contraction. Scanning electron microscopy revealed well-developed plate-like morphologies characteristic of W-type hexaferrites, independent of composition.
Magnetic characterization showed that variations in Co and Sr substitution significantly affected magnetic anisotropy and coercivity, resulting in corresponding shifts in the ferromagnetic resonance frequency (fFMR). In the Sr-substituted system, fFMR shifted toward higher frequencies with increasing Sr content up to x = 0.85, whereas excessive substitution (x = 0.90) led to a reversal toward lower frequencies, suggesting the existence of an optimal substitution range.
Electromagnetic absorption measurements demonstrated that the x = 0.85 composition exhibited excellent reflection loss characteristics near 6 GHz and maintained effective absorption performance even under thin thickness conditions (1.0–1.2 mm), which are compatible with RF SiP package constraints. These results indicate that Sr-substituted W-type hexaferrites are promising candidates for ultra-thin EMI absorber applications in high-density RF packaging environments.

목차 (Table of Contents)

• 1. 서론 1
• 1.1 전자기파 흡수와 강자성 공명(FMR) 3
• 1.2 W-type 육방정 페라이트와 조성 설계 전략 4
• 1.3 반사손실(RL), 임피던스 매칭 및 RL Map의 의미 6
• 1.4 연구 목적 7
• 2. 실험 방법 9
• 2.1 시료 합성 9
• 2.1.1 BaZn2₋xCoxFe16O27 분말의 합성 (System 1) 9
• 2.1.2 Ba1₋xSrxZnCoFe16O27 분말의 합성 (System 2) 10
• 2.1.3 페라이트–에폭시 복합체 시편 제작 10
• 2.2 결정 구조 분석 11
• 2.3 미세구조 관찰 11
• 2.4 자기적 특성 분석 12
• 2.5 전자기파 흡수 특성 평가 12
• 3. 실험 결과 및 고찰 (BaZn2₋xCoxFe16O27) 13
• 3.1 결정 구조 분석 (XRD) 13
• 3.2 미세구조 분석 (SEM) 14
• 3.3 자기적 특성 분석 (M–H Curve) 15
• 3.4 복소 투자율 및 강자성 공명(FMR) 특성 17
• 3.5 반사손실(RL) Spectra 및 RL Map 18
• 3.6. 요약 20
• 4. 실험 결과 및 고찰 (Ba1₋xSrxZnCoFe16O27) 21
• 4.1 결정 구조 분석 (XRD) 21
• 4.2 미세구조 분석 (SEM) 22
• 4.3 자기적 특성 분석 (M–H Curve) 23
• 4.4 복소 투자율 및 강자성 공명(FMR) 특성 25
• 4.5 반사손실(RL) Spectra 및 RL Map 26
• 4.6 요약 29
• 5. 결론 (Conclusion) 30