Integrated inductors with soft magnetic core based on Powder MEMS technology

The Powder MEMS technology developed at Fraunhofer ISIT offers a wide range of possibilities in the fabrication of inductors and transformers with magnetic core on a substrate (e.g. silicon, FR4) for high frequency applications.

The soft magnetic powder is agglomerated by atomic layer deposition (ALD) in the cavities. This solidifies the soft magnetic particles (diameter 1-20µm) by means of a thin dielectric layer (50nm), so that the particles are electrically connected to each other only at the contact surfaces and consequently hardly allow eddy currents. Thus, these components offer great advantages in high frequency applications (switching power supplies with 1-100MHz). The manufacturing process allows operating temperatures of the inductors up to 400°C, enabling a new level of integration and the achievement of higher power densities in products such as a power supply in a chip or package.

Because of this back-end-of-line compatible method, there are great opportunities for integration solutions. Especially for high frequency switching power supplies (SMPS, POL converters), many advantages can be achieved from an electrical and thermal point of view through integration, thus achieving higher power densities in the power supplies of typical applications, such as smart homes, IoT, multimedia consumer market etc.

Powder MEMS technology meets power electronics

PowderMEMS Use case: Microcoils in a DC/DC converter

  • Development and investigation of microcoils (80-200nH) for high frequency applications (1-80MHz).
  • Development of simulation tools and generation of material parameters for future coil designs.
  • Commissioning of a DC/DC converter (20MHz) with micro coil

Passive components for switching power supplies (microcoils)

By applying the powder technology for soft magnetic cores of a coil and the use of a micro coil in a DC/DC converter

Goal: Integration solution of coil and other components   

  • Power density
  • Reduction of parasitic variables
  • Optimized cooling
  • "Power supply on-a-chip
  • Optimized coil/transformer designs

Structure of the coil samples

  • Filling of the cavities with soft magnetic powder
  • REM examinations
  • Winding with 8 turns of copper wire (50µm - 220µm)

Characterization of the coil samples

  • Soft magnetic Fe coil core
  • Hand wound coils with 100µm copper wire on an impedance analyzer (Agilent 4294A) from 100kHz to 100MHz

Investigations by means of FEM simulations

  • Software: Comsol Multiphysics
  • Electromagnetic studies
  • Thermal tests

Prototype - Efficient boost converter as proof-of-concept

  • GaN transistor with a switching frequency of 20MHz
  • Coil sample P04 (L=150nH and R=0.6Ω @ 20MHz)
  • Power up to 20W
  • High measured efficiency

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