Engineers working at the University of Illinois and Stanford University in the US together with researchers at Hefei University of Technology in China and the University of Twente in the Netherlands, have developed a technique to manufacture on-chip coils with inductance values of tens of millitesla for integration in silicon chips.

The technique involves the use of fully integrated, self-rolling magnetic nanoparticle-filled tubes. The resulting coil provides a condensed magnetic field distribution and energy storage in 3D space while keeping the device footprint small enough to be integrated onto a chip. The research results are published in the journal Science Advances.
The self-winding process. Video: Xiung Li

The process is self-rolling

Printed coils are conventionally printed in a single plane on the chip substrate. The coil’s value of inductance is governed by the number of turns. The team of researchers developed 3D inductors using 2D processing by switching to a rolled membrane technique, which allows the wire to spiral out of the plane and uses a thin insulating film to separate the coils. Inductors produced in this way took up only 1% of the space of conventionally manufactured 2D inductors.

Add an iron core

Iron-cored inductors offer better efficiency and the team have developed a method to infuse an iron-oxide nanoparticle solution around the coil structure. It dries to form a solid iron deposit inside the tube which improves the coils properties and makes the technique applicable to a wider range of applications. The teams are refining the process and looking into methods to improve heat dissipation from the structure.