Ultra-Thick Electroplated CoPt Magnets for MEMS

This paper reports the fabrication and magnetic characterization of very thick (50+ μm) 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/m2) and faster plating rates (42 μm/h) compared with previously published work. The magnetic CoPt alloy is co-plated in single electroplating bath and subsequently annealed at 675 °C for 30 min to induce a phase transformation to the high-coercivity L10 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 °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.