Common Amorphous Materials for Magnetic Components in AI Servers

I. Core Amorphous Material Systems

1. Fe-Based Amorphous Soft Magnetic Strips and Powders (Fe–Si–B Series)

• Typical Composition: Based on rapidly quenched strips, such as Fe₇₃.₅Si₁₃.₅B₉Cu₁ (FINEMET), and variants like Fe–Si–B–C, Fe–Si–B–Cr.
  
• Characteristics: High resistivity, low coercivity, low hysteresis and eddy current losses, suitable for high-frequency, low-loss applications.
  
• Forms and Processes: Powder forms can be prepared via atomization techniques (gas, water, or combined gas-water atomization) for subsequent compacting and molding.
  
• Application Scenarios: EMI common-mode inductors, PFC inductors, isolation transformers, etc.
  

2. Fe–Co-Based Amorphous Alloys

• Typical System: e.g., Fe–Co–B–Si–Nb, possessing extremely high saturation magnetization (approx. 1.9 T) and very low coercivity.
  
• Advantage: Balances high saturation flux density (Bs) with high-frequency, low-loss characteristics.
  
• Suitable Applications: High-end common-mode/differential-mode cores, power inductors, etc., requiring trade-offs between performance, cost, and material brittleness.
  

3. Co-Based Amorphous Alloys

• Typical System: e.g., Co–Fe–B–Si, characterized by ultra-high initial permeability (up to 10⁵ magnitude) and broad-frequency impedance characteristics.
  
• Applicable Frequency Range: 150 kHz – 30 MHz.
  
• Primary Application: EMI input/output filtering in server power supplies, used for common-mode noise suppression.
  

4. Fe-Based Amorphous/Nanocrystalline Composites and Bulk Metallic Glasses (BMG)

• Fabrication Process: Preparation of bulk or composite cores via powder metallurgy combined with techniques like Spark Plasma Sintering (SPS).
  
• Material Properties: Advantages include high density, capability for complex shapes, and low losses.
  
• Research Progress: Amorphous systems like FeSiBCCr show promising soft magnetic properties and process feasibility.
  
• Application Direction: Suitable for exploration in molded inductors and high-power-density magnetic components.
  

II. Correspondence Between Typical Devices and Material Selection

The selection pattern reflects the overall trend of 'front-stage amorphous/nanocrystalline + rear-stage ferrite,' and the preference for amorphous/nanocrystalline powder cores in molded inductors.

III. Core Engineering Selection Points

Frequency and Loss

• The mainstream design frequency is 90–120 kHz. Advancing to 200–300 kHz requires strict control of core and copper losses. Amorphous materials have clear advantages in high-frequency, low-loss applications, but evaluation must be combined with specific B-H curves and temperature rise margins.
  

DC Bias and Saturation

• Focus on the material's saturation flux density (Bs) and DC superposition characteristics at operating temperatures of 100–120°C to avoid drastic inductance drop and thermal runaway at high temperatures.
  

Process and Reliability

• Amorphous powders require(coordination with) insulation/coating and densification processes (e.g., SPS) to balance resistivity, loss, mechanical strength, and thermal stability. Production consistency and stability are key thresholds.
  

IV. Typical Applications in AI Server Power Supplies

High-Frequency Isolation Transformers and Inductors in SST (Solid-State Transformers)

• In the 800V HVDC to 48/12V power chain, SST achieves high efficiency and miniaturization through high-frequency isolation and bidirectional energy control. Amorphous/nanocrystalline cores can reduce core loss by approximately 60%–80% compared to traditional silicon steel, achieving overall efficiency above 98%, significantly reducing the volume of magnetic components, and adapting to MW-level modular SST systems.
  

AC-DC Rectification / PFC Inductors

• Under conditions of high current, low ripple, and high-frequency operation (hundreds of kHz), amorphous/nanocrystalline materials, with their high permeability, low coercivity, and low high-frequency loss, can effectively reduce inductor volume and copper/magnetic losses. Suitable for topologies like three-phase Vienna PFC and Totem-Pole PFC, they are key materials for high-power-density rectification stages.
  

DC-DC Multi-Phase Buck Inductors (Molded Inductors)

• GPU/ASIC power delivery demands high current, low DCR, and low AC copper loss. Molded inductors using amorphous/nanocrystalline powder cores can maintain low loss and relatively high saturation flux density at higher frequencies, balancing high efficiency, small size, and thermal stability to meet VRM requirements for low noise and high transient response.
  

EMI Common/Differential Mode Filter Inductors

• The high permeability and broad-frequency, high-impedance characteristics of amorphous/nanocrystalline materials effectively cover the conduction and radiation noise suppression band of 150 kHz–30 MHz. They are suitable for filtering at the AC input and DC output of AI servers, improving the overall machine's EMI compliance margin.
  

Isolation and Distribution Transformers in Data Center HVDC Links

• For HVDC architectures evolving towards 240V/336V/400V/800V, high-frequency transformers using amorphous/nanocrystalline can replace traditional line-frequency silicon steel transformers, significantly reducing no-load and load losses, decreasing volume, and improving the efficiency and power density of the power supply chain.
  

V. Key Considerations for Selection and Implementation

Frequency and Loss Trade-off

• The advantages of amorphous/nanocrystalline in core loss and temperature rise are significant in the 200–500 kHz range. At higher frequencies, it is necessary to combine winding structures (e.g., Litz wire, foil winding, and layer design) to control AC resistance and parasitic capacitance.
  

DC Bias Capability

• The material's Bs value and DC superposition characteristic curve at the high-temperature operating point (100–120°C) must be evaluated to prevent transient saturation.
  

Process and Reliability

• The quality of the insulation coating and the level of the densification process for amorphous powder cores directly affect their voltage withstand capability, thermal cycling reliability, and production consistency.
  

Synergy with Ferrites

• Ferrites are more suitable for high-frequency, low-power, high-impedance scenarios. Amorphous/Nanocrystalline materials excel in medium-to-high frequency, medium-to-high power isolation, and power inductors. The two are often used synergistically in AI power supply chains.
  

VI. Cutting-Edge Developments and Trends

High-Bs Amorphous Alloys Driving Power Density Increase

• With the aid of machine learning in alloy design, Fe-based amorphous systems with Bs > 1.85 T (up to approx. 1.92 T) and coercivity Hc ≈ 1.2 A/m have been developed. This provides a material foundation for smaller, lighter high-frequency power magnetic components, aligning with the pursuit of ultimate efficiency and power density in AI servers.