1000x boost for on-chip 3D inductors

January 24, 2020 //By Nick Flaherty
A scanning electron microscope micrograph of a rolled microinductor architecture, approximatley 80 micrometers in diameter and viewed from one end looking inward Courtesy Xiuling Li
An international team from the US, Europe and China has boosted the performance of on-chip 3D inductors by 1000x to tens of millitesla.

The team of engineers from the University of Illinois and the University of Twente, The Netherlands, has boosted the performance of its 3D inductors by 1000x to embed in silicon chips.

The team developed a microchip inductor capable of tens of millitesla-level magnetic induction by using fully integrated, self-rolling magnetic nanoparticle-filled tubes. This provides a condensed magnetic field distribution and energy storage in 3D space while keeping the tiny footprint needed to fit on a chip. 

Traditional microchip inductors are relatively large 2D spirals of wire, with each turn of the wire producing stronger inductance. In a previous study, Li’s research group developed 3D inductors using 2D processing by switching to a rolled membrane paradigm, which allows for wire spiraling out of plane and is separated by an insulating thin film from turn to turn. When unrolled, the previous wire membranes were 1 millimeter long but took up 100 times less space than the traditional 2D inductors. The wire membranes reported in this work are 10 times the length at 1cm, allowing for even more turns – and higher inductance – while taking up about the same amount of chip space.

“A longer membrane means more unruly rolling if not controlled,” said Xiuling Li, electrical and computer engineering professor at the University of Illinois and interim director of the Holonyak Micro and Nanotechnology Laboratory. “Previously, the self-rolling process was triggered and took place in a liquid solution. However, we found that while working with longer membranes, allowing the process to occur in a vapor phase gave us much better control to form tighter, more even rolls.”

Another key development in the new microchip inductors is the addition of a solid iron core. “The most efficient inductors are typically an iron core wrapped with metal wire, which works well in electronic circuits where size is not as important of a consideration,” said Li. “But that does not work at the microchip level, nor is it conducive to the


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