Researchers at the University of Florida have developed tiny magnetic devices that could support more compact power delivery for computer chips. The work focuses on inductors, components used in voltage regulators to help provide circuits with a stable supply of electricity.
The team fabricated stripline microinductors with a magnetic nanocomposite made from iron oxide nanoparticles and nickel. Measurements showed approximately 1.6 nanohenries of inductance, more than twice that of comparable devices without a magnetic core.
Inductors are difficult to miniaturize because reducing their dimensions generally lowers the inductance available from a given design. Adding magnetic material around the conductor can increase the magnetic flux and allow a smaller structure to provide more inductance. However, devices operating at higher switching frequencies also require materials that respond quickly without excessive energy loss.
The researchers used a process called electroinfiltration, in which nickel was electrochemically deposited into the spaces between iron oxide nanoparticles. The resulting composite was incorporated into a structure containing an electrically insulated copper strip between upper and lower magnetic layers.
Fabrication presented a challenge because the insulation over the copper had steep sidewalls, making it difficult to create a continuous upper magnetic layer. The team used heat-softened photoresist to form a rounded profile. This allowed the copper thickness to increase from approximately 2 to 6 micrometers while maintaining magnetic coverage, reducing the conductor’s winding resistance.
The optimized device reached a peak quality factor, or Q, of 5.3 at 150 megahertz. That represented a 58% increase over the original process, which had a peak Q of 3.35. The quality factor reflects the balance between inductive behavior and electrical loss at a given frequency; it is not a measurement of the efficiency of a complete voltage regulator.
The researchers also tested a separately fabricated one-port inductor under direct-current bias. Its inductance remained approximately stable through 330 milliamperes when measured at 1 megahertz, indicating no measurable magnetic saturation within that test range. The result does not establish the current rating of the optimized device at 150 megahertz.
The approach could eventually help place power-conversion components closer to the circuits they supply, including within semiconductor packages or integrated power supplies. The researchers emphasize that further work is needed on heating, reliability and performance in complete converters. Of 97 tested devices, 64 were functional, showing that fabrication yield also requires improvement.
The study was conducted by Brenden M. Mears, Noah Morgan, Jennifer S. Andrew, David P. Arnold and Sai Pranesh Amirisetti at the University of Florida. It was published in the Journal of Micromechanics and Microengineering under the title “Stripline microinductors using electroinfiltrated nickel-iron oxide nanocomposites for power supply on chip applications.”
Sources: Phys.org.