Monolithically-fabricated laminated inductors with electrodeposited silver windings

This paper presents batch microfabrication and experimental characterization of solenoid inductors with electrodeposited silver windings and laminated core. To enable high-frequency operation, the metallic magnetic core consists of multiple air-insulated, electroplated micron-thick permalloy (Ni₈₀Fe₂₀) laminations, with total core thicknesses up to tens of microns. The core is achieved by sequential electrodeposition of permalloy and copper, followed by selective removal of the copper, thereby releasing the core laminations. Electroplated silver is selected as winding material for its low resistivity and to withstand the copper etching required during core release. Release of the core laminations is the final inductor fabrication step, reducing potential process-induced damage to the core. Two inductors sharing one laminated core in a transformer geometry are fabricated, and exhibit inductances of approximately 100 nH at 5 MHz, resulting in an inductance density of 29 nH/mm². This process demonstrates processing compatibility of using silver windings with highly-laminated, fully-integrated magnetics.