High-frequency micro-machined power inductors (original) (raw)

Comparative Study of Microfabricated Inductors / Transformers for High Frequency Power Applications

IEEE Transactions on Magnetics, 2017

This paper presents a comparative study on different microfabricated inductors (microtransformers), which are suitable for high frequency power application. The main topic of this study is comparing and analyzing the effect of some factors like material type, number of turns, and coil form on microinductor performance considering a fixed chip size, fixed magnetic core size, and core form. Two different microtransformer designs with different magnetic core materials are considered in this work. The core materials used in this work are NiFe45/55 and CoFe45/55. Also, two types of device packages are developed, namely QFN and FR4 embedded packages. For device testing, different high frequency switching regulators available on the market are used. This study shows the influence of different parameters on the performance of a certain high frequency application. In this paper, we discuss the influence of the design, magnetic material, and package type on thermal performance and the efficiency of the power application.

Metal-embedded SU-8 Slab Techniques for Low-resistance Micromachined Inductors

International Journal of Electrical and Computer Engineering (IJECE), 2018

This work presents a new fabrication technique for micro power inductors by using metal-embedded SU-8 slab molding techniques. The proposed technique uses X-ray lithography to fabricate high-aspect-ratio LIGA-like microstructures in form of embedded structures in the SU-8 slab. This process was applied to fabricate an inductor's windings with an aspect ratio of 10, which can provide very low resistance but still preserve a small form factor and low profile. Inductors were designed as pot-core structures with overall heights of 370 μm and embedded with 250-μm-thick windings. From the advantage of metal embedded SU-8 slab techniques, 8 μm-thick permalloy core could be fabricated by electroplating around the winding in a single step that could help simplify the process. Four types of inductors were fabricated with 3, 5, 10, and 16 turns in the area of 1.8 to 9.5 mm2. The measured inductance was in the range of 70 nH to 1.3 μH at 1 MHz and DC resistance of 30-336 mΩ for 3-16 turns, respectively. The DC resistance of fabricated inductor was low, as expected, and showed good result compared with the results in literature. Keyword: High aspect-ratio inductors Metal-embedded SU-8 slab Micro power inductors Micromachined inductors X-ray lithography 1. INTRODUCTION Portable electronic devices have become a daily necessity. Over time, these fabricated devices have decreased in size and increased in efficiency. However, owing to their limited size, these devices have only single batteries supplying current to each circuit despite varying DC voltage requirements. Thus, the DC-DC converter circuit is an essential component of such devices and is determinant of device efficiency, and more efficient converter circuits have been continuously developed. The inductive-switching type circuit is currently very popular because of its provision of great efficiency with high power density. At present, the circuit is normally operated in the megahertz range [1]. In some literature, the circuits were designed to operate at a frequency of up to 100 MHz [2]; however, the efficiency at an extremely high frequency is still limited because of switching loss. The advantage of working at a megahertz range could help decrease the inductance required. In addition, the inductor's size could be smaller and still be capable of being packed with ICs, thus facilitating in increasing the power density [3]. However, fabricating a highly efficient integrated inductor with a limited area has become a challenge because DC resistance plays an important role in inductor efficiency in a DC-DC converter circuit, as the majority of current flowing through the inductors is DC current. Thus, with the area constraint, it is hardly possible to fabricate the windings of a low-resistance inductor by using conventional thin film technology.