High-Inductance-Density MEMS 3D-solenoid Transformers with Inserted Thin-Film Ferrite Magnetic Core For On-Chip Integrated DC-DC Power Conversions

This paper presents high-inductance-density MEMS 3D-solenoid magnetic core transformers that are wafer-level fabricated by a novel thick-metal micro-casting technique. With the embedded thin-film high-permeability ferrite core, an over 7 times boost in inductance (from 43.3 nH to 334.2 nH) and 25% increment in coupling coefficient (from 0.76 to 0.96) are achieved. For the batch-fabricated transformer in a tiny footprint of 6 mm
²
, an over 1.6 A saturated current and one of the best-reported power transfer efficiency of 89.5% at a lower frequency of 10 MHz are demonstrated. The proposed magnetic core transformers are ideal for high-efficiency integrated DC-DC power conversion applications.