A new hybrid technology for planar microtransformer fabrication

We have developed a new printed circuit board ( PCB) technology adapted for the fabrication of ultra-flat microtransformers. The two outer layers of the PCB stack comprise the electrical windings of the inductive devices, while the inner layer is made of a micro-patterned amorphous magnetic ribbon with extremely high relative magnetic permeability (mu(r) approximate to 100000). Two basic configurations were considered; one being based on a toroidal magnetic core and the other on a rectangular (E-shaped) magnetic core. The electrical properties of the microtransformers have been studied as a function of frequency. Inductances were found to be as much as 30 mu H at 1 kHz, a relatively high value compared to microtransformers of similar size. Despite a relatively high leakage flux, voltage transformation efficiencies were measured between 89% and 98%. The high performance of these devices is primarily due to the use of the high permeability magnetic core. The characteristics of these devices are discussed in light of geometrical considerations and finite element calculations. (C) 1998 Elsevier Science S.A. All rights reserved.