Polymer Magnetic Composite Core Based Microcoils and Microtransformers for Very High Frequency Power Applications.

Saravana Mariappan,Ali Moazenzadeh,Ulrike Wallrabe

doi:10.3390/mi7040060

Saravana Mariappan, Ali Moazenzadeh + Show 1 more

Open Access

https://doi.org/10.3390/mi7040060

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Journal: Micromachines	Publication Date: Apr 5, 2016
Citations: 10	License type: CC BY 4.0

Affiliation: University of Freiburg

Abstract

We present a rapid prototyping and a cost effective fabrication process on batch fabricated wafer-level micro inductive components with polymer magnetic composite (PMC) cores. The new PMC cores provide a possibility to bridge the gap between the non-magnetic and magnetic core inductive devices in terms of both the operating frequency and electrical performance. An optimized fabrication process of molding, casting, and demolding which uses teflon for the molding tool is presented. High permeability NiFeZn powder was mixed with Araldite epoxy to form high resistive PMC cores. Cylindrical PMC cores having a footprint of 0.79 mm were fabricated with varying percentage of the magnetic powder on FR4 substrates. The core influence on the electrical performance of the inductive elements is discussed. Inductor chips having a solenoidal coil as well as transformer chips with primary and secondary coils wound around each other have been fabricated and evaluated. A core with 65% powder equipped with a solenoid made out of 25 µm thick insulated Au wire having 30 turns, yielded a constant inductance value of 2 µH up to the frequency of 50 MHz and a peak quality factor of 13. A 1:1 transformer with similar PMC core and solenoidal coils having 10 turns yielded a maximum efficiency of 84% and a coupling factor of 96%. In order to protect the solenoids and to increase the mechanical robustness and handling of the chips, a novel process was developed to encapsulate the components with an epoxy based magnetic composite. The effect on the electrical performance through the magnetic composite encapsulation is reported as well.

Highlights

The ongoing trend towards miniaturization of electronics with proliferation of functionality and performance requires compact and efficient power management at microsystem platforms.The aforementioned aspects are addressed by the power semiconductor industries and various research groups through their ability to deliver advanced processing and functional integration by driving the power management system in the very high frequency regime (VHF, 30 to 300 MHz) [1].A major challenge is that the further miniaturization of the power modules is limited by the presence of bulky inductive components though the inductance needed at the VHF frequencies are relatively low compared to the systems operating at lower frequencies [2,3].Typically, inductive components at VHF regime are implemented using bulky air core devices
The inductance of a solenoidal coil wound around a magnetic core is directly proportional to the magnetic permeability of the core
In the polymer magnetic composite (PMC) cores, two kinds of eddy current losses can be identified, one due to the current circulating within the insulated magnetic particles and the other due to the current around the clusters of particles

Summary

Introduction

The ongoing trend towards miniaturization of electronics with proliferation of functionality and performance requires compact and efficient power management at microsystem platforms.The aforementioned aspects are addressed by the power semiconductor industries and various research groups through their ability to deliver advanced processing and functional integration by driving the power management system in the very high frequency regime (VHF, 30 to 300 MHz) [1].A major challenge is that the further miniaturization of the power modules is limited by the presence of bulky inductive components though the inductance needed at the VHF frequencies are relatively low compared to the systems operating at lower frequencies [2,3].Typically, inductive components at VHF regime are implemented using bulky air core devices. The aforementioned aspects are addressed by the power semiconductor industries and various research groups through their ability to deliver advanced processing and functional integration by driving the power management system in the very high frequency regime (VHF, 30 to 300 MHz) [1]. A major challenge is that the further miniaturization of the power modules is limited by the presence of bulky inductive components though the inductance needed at the VHF frequencies are relatively low compared to the systems operating at lower frequencies [2,3]. Inductive components at VHF regime are implemented using bulky air core devices. Micromachines 2016, 7, 60 a high inductance density, at VHF regime the frequency dependent core losses become dominant [4]. The process complexity remains as an impediment [9,10]

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