Key Takeaways & Executive Findings
- •• • As-deposited films are amorphous; coercivity decreases and saturation magnetization increases with thickness, stabilizing at 400 nm, which is optimal for device integration. • • Annealing at 773 K and 873 K precipitates nanocrystalline α-Fe; exchange coupling between nanocrystals and amorphous matrix enhances soft magnetic properties. • • Film annealed at 873 K for 30 min with heating rate 25 K/s achieves coercivity of 0.8 A/m and saturation magnetization of 1.45 T, enabling high-frequency operation with low eddy current losses. • • Rapid thermal processing controls thermal gradient to produce smaller nanocrystals, reducing coercivity without additional transition metals, offering a cost-effective route for high-performance inductors.
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Abstract
The influence of thickness and annealing treatment on the microstructure and soft magnetic properties of Fe−Si−B−Cu−Nb alloy (Finemet) thin films prepared by magnetron sputtering was systematically investigated. As-deposited films are amorphous; coercivity decreases and saturation magnetization increases with thickness, stabilizing at 400 nm. Annealing at 773 K and 873 K precipitates nanocrystalline α-Fe within the amorphous matrix. Exchange coupling between nanocrystals and the amorphous matrix enhances soft magnetic properties. Rapid thermal processing (RTP) controls the heating rate to minimize grain size and optimize nanocrystal distribution, achieving low coercivity and high saturation magnetization without additional transition metals. The film annealed at 873 K for 30 min with a heating rate of 25 K/s exhibits a coercivity of 0.8 A/m and saturation magnetization of 1.45 T. Compared to the 773 K annealed film, the 873 K annealed film shows significantly lower coercivity due to smaller precipitated nanocrystals. RTP with controlled thermal gradient enables even smaller nanocrystals, further enhancing magnetic properties. These results demonstrate that RTP-treated Finemet films are promising for high-frequency, miniaturized, and integrated electronic devices.
1. Introduction
High-frequency, miniaturized, and integrated electronic devices demand soft magnetic thin films with low coercivity and high saturation magnetization. Conventional wound and laminated inductors are bulky and incompatible with silicon integration. Amorphous alloys offer low coercivity due to lack of grain boundary pinning and high resistivity for reduced eddy current losses, but their saturation magnetization is limited. Nanocrystalline alloys like Finemet (Fe73.5Si13.5B9Cu1Nb3) combine high saturation magnetization with low coercivity, yet achieving optimal nanocrystal size and distribution remains challenging.
Existing annealing methods often require transition metal additions or prolonged thermal treatments that coarsen grains and degrade soft magnetic properties. This study employs rapid thermal processing (RTP) to control heating rate and thermal gradient, minimizing grain size and optimizing nanocrystal distribution. The resulting Fe−Si−B−Nb−Cu thin film exhibits a coercivity of 0.8 A/m and saturation magnetization of 1.45 T, demonstrating a scalable route for high-performance integrated inductors.
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Jun-jie LIU, Zhao-guo QIU, Yi-ming ZENG, Zhi-gang ZHENG, Gang WANG, Zhi-peng HOU, Hao-liang LIU, De-chang ZENG, Ping LIU (2026). High-Performance Finemet Alloy Thin Film with Amorphous/Nanocrystalline Structure Treated by Rapid-Thermal Process. Transactions of Nonferrous Metals Society of China (中国有色金属学报). https://doi.org/10.1016/S1003-6326(26)67064-1
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Frequently Asked Questions
What is the optimal film thickness for maximizing soft magnetic properties?
The film with thickness of 400 nm demonstrates superior magnetic performance, as coercivity decreases and saturation magnetization increases with thickness until stabilizing at this value.
How does rapid thermal processing (RTP) improve magnetic properties compared to conventional annealing?
RTP controls the heating rate (e.g., 25 K/s) to minimize grain size and optimize nanocrystal distribution, achieving lower coercivity (0.8 A/m) and higher saturation magnetization (1.45 T) without additional transition metals.
What is the role of exchange coupling in enhancing soft magnetic properties?
Exchange coupling between nanocrystalline α-Fe precipitates and the amorphous matrix significantly enhances soft magnetic properties by averaging out magnetocrystalline anisotropy.
Why does annealing at 873 K yield lower coercivity than at 773 K?
Annealing at 873 K produces smaller-sized nanocrystals, which reduces coercivity due to more effective exchange coupling and reduced domain wall pinning.
Can these films be scaled for industrial production of integrated inductors?
Yes, the magnetron sputtering and RTP processes are compatible with semiconductor fabrication, and the achieved properties (0.8 A/m coercivity, 1.45 T saturation magnetization) meet requirements for high-frequency inductors.
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