MEMS based electrochemical process for fabrication of laminated micro-inductors on silicon

Soft metallic magnetic alloys (such as Co, Ni and Fe based alloys) have been extensively used as core material in integrated inductors and transformers for DC-DC conversion. Although these materials have excellent soft magnetic properties such as high saturation flux density, low coercivity and high permeability; high electronic conductivity makes them susceptible to eddy current losses. As a result, core material thickness is often limited by the skin depth which in turn reduces the inductance density. Laminated magnetic films, where the active layers are separated by a dielectric film can increase the overall core thickness without compromising on its power handling capability. In this work, a CMOS compatible electrochemical-resist-electrochemical based core lamination deposition technique is demonstrated whereby a laminated top magnetic core is fabricated with a self-assembled and selective metallization process on the top SU-8 passivation layer with 2.5 μm Ni₈₁Fe₁₉. The process is site-selective, shows uniform deposition, has excellent step coverage and ideal for metallization of recessed regions in MEMS devices. Moreover, a high frequency measurement of laminated structure suggests uniform permeability for ~ 500 MHz applications.