Magnetophoresis Assisted Capillary Assembly of Cobalt Nanorods: A New Source of Permanent Magnets for MEMS

This paper presents the fabrication of high-performance micro-magnets for the electromagnetic transduction of MEMS. The fabrication method relies on the use of nickel microstructures electroplated onto silicon substrates to control the capillary assembly of cobalt nanorods via magnetophoresis under an external magnetic field. The resulting sub-millimeter size permanent magnets with thicknesses of up to
$150\ \mu \mathrm{m}$
produce a stray field of 30 mT at a distance of
$100\ \mu \mathrm{m}$
. We demonstrate that this magnetic induction is sufficient to actuate a silicon microcantilever by means of the Lorentz force and that the MEMS resonance frequency can adequately be measured using integrated piezoresistances. This novel room-temperature synthesis approach is foreseen to facilitate the integration of high-performance magnets into MEMS.