Ultra-Thick Electroplated CoPt Magnets for MEMS

摘要

This paper reports the fabrication and magnetic characterization of very thick (50+ mu m) and high-performing (coercivity up to 850 kA/m; energy products up to 75 kJ/m(3)) electroplated permanent magnets microfabricated on silicon substrates. Intended for MEMS applications, the fabrication process yields higher areal magnetic energy density (5.6 J/m(2)) and faster plating rates (42 mu m/h) compared with previously published work. The magnetic CoPt alloy is co-plated in single electroplating bath and subsequently annealed at 675 degrees C for 30 min to induce a phase transformation to the high-coercivity L1(0) CoPt phase. Compared with the previous literature on electroplated CoPt films, four main accomplishments are reported: 1) optimization of the underlying seed layer metallurgy to improve film adhesion and inhibit interfacial diffusion/reactions; 2) development of a warm-bath (50 degrees C), high-current-density (300-2000 mA/cm(2)) electroplating process that dramatically increases plating rate while maintaining good magnetic properties; 3) study of the electroplating bath longevity; and 4) exploration of the nanostructure of the electroplated magnets by TEM/STEM.