Fully Integrated Spiral-type Microtransformers on a Silicon Substrate

Abstract

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