Packaging-compatible microtransformers on a silicon substrate

Surface micromachining techniques are utilized to realize microtransformers for being integrated with a multi-chip package, allowing compact integration with chips, sensors, and other components. Two different microtransformers with two-layer vertically stacked spiral-type copper conductor lines and permalloy magnetic cores have been designed and fabricated. Low temperature processes are only chosen for fabricating these microtransformers. The fabricated microtransformers have been tested and compared for finding out better geometries for microtransformers. Electroplated thick permalloy cores and copper coils are utilized for obtaining better performance characteristics in the intermediate frequency range. The fabricated microtransformer has a turn ratio of 1, coupling coefficient of 0.85, dc resistance of 3.3 ohms, and gain characteristics of -5 dB, respectively. These devices have high current capability (up to 2A steady DC current) and are suitable for low power converter applications.