Thick Multilayered Micromachined Permanent Magnets With Preserved Magnetic Properties

This paper presents microfabricated permanent magnets possessing a multilayer structure that preserves the high magnetic energy density of thinner magnetic films, while simultaneously reducing average residual stress of the films and achieving a significant magnetic thickness. Many magnetic microelectromechanical systems (MEMS) devices heavily rely on the availability of thick (a few tens to hundreds of micrometers, high-energy-density permanent magnet components able to be deposited in a fully integrated and CMOS-compatible manner (process temperature less than 450°C). However, it is observed that increasing magnetic film thickness typically causes a concomitant decrease in magnetic properties such as maximum energy density and increased mechanical instability (cracking and delaminating, due to the increased elastic strain energy stored in the films as magnetic volume increases), both of which limit the maximum total magnetic energy of these small-scale integrated magnets. The microlaminated permanent magnet presented here utilizes sequential multilayer electroplating in which the alternating layers of relatively thin magnetic films (CoNiP, micrometer range) and non-magnetic materials (Cu, a few tens of nanometer to micrometer range) are electrodeposited in a multilayer fashion realizing thick laminated permanent micromagnets with improved total magnetic energy as compared with their non-laminated counterparts. Low interface roughness has been demonstrated to play an important role in preserving the component magnetic thin layer properties in the multilayer configuration.