Electrical performance of microtransformers for DC-DC converter applications

Abstract

This paper presents the electrical performances of the fabricated microtransformers. Measurements for open-circuit and short-circuit impedance up to a frequency of 100 MHz are presented. The measured results are compared with predictions obtained from models based on an analytical approach. The use of a microtransformer in a 2-MHz dc-dc converter is reported. An efficiency of 40% for a power density of 1.2 W/cm 2 was measured.Index Terms-Analytical model, high power density, microtransformers.

Pulse reverse plating for integrated magnetics on Si

“…Ni 45 Fe 55 was chosen for the fabrication of microtransformer cores due to its relatively high saturation flux density (1.6 T), resistivity (48 mO cm) and anisotropy field (9.5 Oe) compared to corresponding properties (1 T, 20 mO cm, 2.5 Oe) of permalloy, making it suitable for operation at our target 5 MHz frequency. Electroplating was chosen as the preferred integration technique over sputtering, PVD or CVD as it is not only an inexpensive and faster approach compared to other techniques but also readily lends itself to the complex 3D topology of our various transformer designs [8,9].In an electrochemical cell, if a voltage is applied across the positive (anode) and negative (cathode) electrodes, the metal ions from the electrolytic solution adjacent to the cathode are deposited on to it, decreasing the concentration of metal ions in the vicinity of the electrode. Consequently, a concentration gradient near the electrode is created and metal ions from relatively higher concentration regions diffuse to the depleted ARTICLE IN PRESS www.elsevier.com/locate/jmmm 0304-8853/$ -see front matter r…”

“…Ni 45 Fe 55 was chosen for the fabrication of microtransformer cores due to its relatively high saturation flux density (1.6 T), resistivity (48 mO cm) and anisotropy field (9.5 Oe) compared to corresponding properties (1 T, 20 mO cm, 2.5 Oe) of permalloy, making it suitable for operation at our target 5 MHz frequency. Electroplating was chosen as the preferred integration technique over sputtering, PVD or CVD as it is not only an inexpensive and faster approach compared to other techniques but also readily lends itself to the complex 3D topology of our various transformer designs [8,9].…”

High efficiency Si integrated micro-transformers using stacked copper windings for power conversion applications

“…Authors use a particular spiral design, racetrack shape, in this work since it is easy to induce uniaxial anisotropy in the core in order to achieve a good frequency response. In previous work [10][11][12][13][14], the authors presented the modeling, design, and test of micro-transformer with relatively large footprint area, e.g. 10s mm2, aimed for 5MHz switching frequency.…”

High-frequency micro-machined power inductors

“…The same process as used in the fabrication of microtransformers was applied here [11], except that two bottom layers of magnetic material were electroplated and patterned rather than previous single layer. Based on this process, one more magnetic core layer can be electroplated, which will be joined to the lower layer of bottom core to form another closed magnetic path, and then enhance the inductance value.…”