Magnetic Materials and Design Trade-Offs for High Inductance Density, High-Q and Low-Cost Power and EMI Filter Inductors

This paper investigates the trade-offs in inductance density and quality factor of inductors with and without magnetic-cores through modeling, design, fabrication and model validation through characterization. Two type of inductors, one for power-supply and the other for EMI filters, are investigated. Parametric analysis was performed to study the enhancement in inductance density without compromising the current handling and efficiency. For EMI filter inductors, the inductance and quality factor (Q) were improved by 13X and 4X respectively with and without magnetic cores. For power inductors, the inductance and quality factor were improved by 5X and 1.6X respectively. The fabricated magnetic core inductors achieved 5X reduction in thickness, compared to the stage-of-the art air-core inductors which use multilayered and thick solenoid.

I. Introduction

Increased power levels in consumer electronic systems are driving the need for integrated power supply modules in 3D architectures for efficient power management. Delivering noise-free power with the required voltage and current levels is a major barrier to such systems, in power efficiency and system miniaturization. Various voltage regulators and noise filters are incorporated currently between the power source and device load in order to regulate the power supply. These regulators consist of a network of switches and storage components such as capacitors and inductors that transfer power to the load at the desired levels. The key barriers to miniaturization, performance and cost in integrated voltage regulators arise from the lack of suitable magnetic materials with required properties such as permeability, loss, frequency-stability and current-handling. Today's inductors for power supply are either components that are surface-mount assembled on the board or integrated in the package or on-chip. Trade-offs between power handling, efficiency and size impose key constraints to inductor design, which forms the key focus of this paper.