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 2.5µm 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 ~500MHz applications. Highlight: Activation and seedless site-selective metallization of SU-8 for top core lamination.Display Omitted In this work a novel electrochemical core lamination process has been demonstrated.High aspect ratio SU-8 polymer structures have been selectively activated and metallized with permalloy.The process has been successfully integrated with CMOS compatible micro-inductor fabrication.This method can be exploited for site-selective metal deposition in MEMS devices and in recessed regions.