In this paper, the development of a CMOS switch buck DC-DC converter fabricated in an organic interposer with an embedded power inductor is described. The power inductor is fabricated by using a magnetic core made of an Fe-based amorphous alloy powder-filler/epoxy composite sheet to form a fully closed magnetic circuit and is embedded in the organic interposer in a lamination process. The fabricated power inductor is located under a CMOS control chip and has a of 3.5-mm-square footprint. The CMOS switch buck DC-DC converter runs at 20 MHz, and the fabricated power inductor has an inductance of 150 nH and Q-factor of 38 at around 20 MHz. Furthermore, the influence of magnetic flux leakage from the embedded power inductor to a copper wiring pattern on the surface was analyzed in a simulation that utilized three-dimensional electromagnetic field analysis software (ANSYS; HFSS). Based on the simulation result, the conduction losses of the inductor were calculated under the assumption of use in a synchronous buck converter operating with a 5-V input and 3.3-V 0.8-A output.
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