Fabrication, Characterization and Comparison of FR4-Compatible Composite Magnetic Materials for High Efficiency Integrated Voltage Regulators with Embedded Magnetic Core Micro-Inductors

Integrated voltage regulators (IVRs) are considered nowadays as major elements in the development of power delivery networks for digital electronics because of their ability to implement point-of-load voltage regulation in multicore microprocessors and system-on-chip (SoC) architectures. Inductive regulators generally enable higher power efficiency over a wide range of conversion voltages. However, high efficiency IVRs require the integration of power inductors with low loss and reduced size at very high frequency. The use of a magnetic material core can reduce significantly the inductor area while increasing the inductance value at the same time. This paper focuses on the fabrication, characterization and modeling of Nickel Zinc (NiZn) Ferrite and Carbonyl Iron powder (CIP) epoxy composite magnet material which will be used as the magnetic core material of an embedded inductor in the PWB for SIP based buck type IVR. The fabricated composite materials and process are fully compatible with FR4 epoxy resin prepreg and laminate (PWB-compatible). The composite materials show (for 85% weigh loading, around 100 MHz at room temperature) a relative permeability between 7.5-8.1 for NiZn-composite (0.78 volume fraction) and between 5.2-5.6 for CIP composite (0.47 volume fraction) and a loss tangent value between 0.24-0.28 for NiZn-composite and 0.09-0.1 for CIP-composite. The variation of the relative permeability and the frequency dispersion parameters of the magnetic composites are evaluated using Maxwell-Garnet Approximation (MGA) mixing rule and a simplified Lorentz and Landau-Lifshitz-Gilbert equation for Debye type relaxation. Evaluation of a buck type IVR based on the measured material properties shows that an embedded solenoidal inductor with an open core made with the NiZn Ferrite and CIP composite magnets can reach peak efficiencies of 91.7 % at 11 MHz for NiZn-composite, 91.6 % at 14 MHz for CIP-composite and 87.5 % (NiZn-composite) and 87.3 % (CIP-composite) efficiencies at 100 MHz for a 1.7V:1.05V conversion.