Fabrication and Characterization of Package Embedded Inductors for Integrated Voltage Regulators

As data centers become more energy efficient, there is a need to improve the power delivery network (PDN) efficiency. Current efficiencies for the 48 V to 1 V multi-stage conversion systems can be as low as 75% or lower, because of multiple down conversion stages and high currents passing through the mother board. Previously, we proposed an inductor power loss metric to characterize the inductors using a custom-built measurement board that considers the small signal response (with and without DC bias) and large signal measurements. In this work, we compare 4 different magnetic materials, HBS1, XVSZ2, XVSZ3 and XVSZ4 (courtesy of Panasonic) in the form of metal polymer composite sheets of 400 μm thickness to fabricate and test the embedded inductors. To increase the inductance of the embedded toroidal inductors, we increase the number of windings along with an increase in the number of cylindrical vias. The new inductors have small dimensions and have high inductances in the range of 200 – 600 nH. They provide a maximum inductance density of 68 nH/mm2 with a current per inductor greater than 2.5 A and 84.7% inductor efficiency. To decrease the DC resistance of the inductors, the copper thickness used is 50 μm.