Silicon molding techniques for integrated power MEMS inductors

Monolithic integration of DC-DC converters with on-chip inductors has emerged as a viable means to reduce size and increase transient performance for portable electronics. MEMS techniques have been used to integrate power inductors on chip, but those MEMS inductors have low power handling capability due to high DC resistance, high core loss or small saturation current. This paper reports a unique silicon-molding technique that is capable of embedding thick electroplated metal layers (both Cu and permalloy) into the silicon substrate, in which through-wafer silicon trenches are used as the electroplating molds. These silicon trenches are coated with SU-8 to enhance electrical isolation and relax the thermal stress. The thickness of the embedded metals is up to that of the silicon substrate which ranges from 200 μm to 500 μm, leading to small DC resistance. Two thick magnetic plates are fabricated on the both sides of the silicon substrate, which are connected by through-wafer magnetic vias to achieve high inductance. A pot-core inductor with a low-frequency inductance of 134 nH, a DC resistance of 9.1 mΩ and over 1 A saturation current has been demonstrated.