Magnetic Cores for High Conversion Ratio Package Embedded Inductors

Inductors play a significant role in power delivery networks that help in supplying voltage to the chiplets when the power FETs (field effect transistors) are in the OFF cycle. Miniaturized inductors in the core of a package help in power regulation at high voltages. However, for higher conversion ratios with V
in
> 5 V, the requirements for magnetic materials become harder to achieve that include: relative permeability of 65, loss tangent (tanδ) < 0.012, and saturation magnetization (H
sat
) of > 6 kA/m. To achieve these targets, we have investigated powders based on Fe 6.35 wt% Si, Fe 50 wt% Ni, and FeCuNbSiB (FINEMET) alloys in the form of toroidal soft magnetic composites with an epoxy-resin as a continuous binding phase. Relative permeability at high frequencies (1 MHz to 1 GHz), Ferro Magnetic Resonance frequency (f
FMR
), and quasi-static hysteresis losses are studied. Using a custom-built board, small signal measurements without DC bias were performed to compare the inductors based on a previously proposed power loss metric R
acx
(effective AC resistance per unit inductance, mΩ/nH) studied on a wide number of toroids and packaged inductors at the packaging research center (PRC). A FeNi-FeSi-BCB based composite has been identified with 110-130% increase in relative permeability (18.5-20) compared to FeSi-BCB in the range of 2-20 MHz, with a saturation magnetic moment of 176.04 emu/g. Ball-milling of FeCuNbSiB powder revealed a significant increase in f
FMR
and a highly stable permeability sweep up to 200 MHz. The frequency stability and average R
acx
between 15-85% duty cycle of buck converter operation (0.11, 0.28, and 0.65 mΩ/nH at 2, 5 and 10 MHz) did not degrade when subjected to Highly Accelerated Stress Testing (HAST). The results are correlated with the material properties to develop a rationale for synthesizing high frequency magnetic cores for applications in power delivery and management.