3D rolled filter cuts chip footprint

Technology News |
By Nick Flaherty

Researchers at the University of Illinois, Urbana-Champaign have developed a rolled 2D filter that can replaced large discrete designs.

The inductive and capacitive elements are printed on a flexible substrate using standard CMOS technology in a single plane and subsequently triggered by the built‐in stress to self‐assemble and roll into cylindrical air‐core architectures. By designing the planar structure geometry and constituent layer properties to achieve a specific number of turns with a desired inner diameter when the device is rolled up, the electrical characteristics can be engineered.

This microtubular self‐rolled‐up membrane (S‐RuM) works in the 1 to 10GHz range and the filter has a footprint of 0.09 mm2 and volume of 0.01 mm3, ten times smaller than discrete filters.

“With the success that our team has had on rolled inductors and capacitors, it makes sense to take advantage of the 2D to 3D self-assembly nature of this fabrication process to integrate these different components onto a single self-rolling and space-saving device,” said Xiuling Li, professor of electrical and computer engineering at the university.

The network layouts of the L and C components are also reconfigurable by selecting appropriate input, output, and ground contact routing topographies.

“The masks we use to form the circuitry on the 2D membrane layers can be tuned to achieve whatever kind of electrical interactions we need for a particular device,” said researcher Mark Kraman. “Experimenting with different filter designs is relatively simple using this technique because we only need to modify that mask structure when we want to make changes.”

The team tested the performance of the rolled components and found that under the current design, the filters were suitable for applications in the 1-10GHz. While the designs are targeted for use in radio frequency communications systems, the team says other frequencies, including in the megahertz range, are also possible based on the ability to achieve high power inductors in past research.

“We worked with several simple filter designs, but theoretically we can make any filter network combination using the same process steps,” said researcher Mike Yang. “We took what was already out there to provide a new, easier platform to lump these components together closer than ever.”

“Our way of integrating inductors and capacitors monolithically could bring passive electronic circuit integration to a whole new level,” Li said. “There is practically no limit to the complexity or configuration of circuits that can be made in this manner, all with one mask set.”

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