Fabrication of NdFeB micromagnets based on vacuum negative pressure injection

Abstract

Micromagnets integrated into microelectromechanical systems devices are widely used in the fields of micro-energy harvesters, micro-actuators, and speakers. A novel method for fabricating NdFeB micromagnets based on vacuum negative pressure injection is presented. The influence of array element shape, size, and injection channel on the surface magnetic field was studied by Maxwell finite element analysis. A circle array of 600 µm diameter and 150 µm spacing could generate a stronger magnetic field at the edge of the magnet array. Micron-sized magnetic powders with a diameter of 5 µm mixed with the SU8 T2010 photoresist were filled into the microcavity on a PDMS (polydimethylsiloxane) elastomer, which was prepared by the SU8 positive membrane. The PDMS elastomer was bonded to the glass substrate and degassed by a vacuum pump to form negative pressure for rapid injection and uniform filling. By selecting a suitable binder and optimizing the mixing ratio of the magnetic powder, a 165 µm thick micromagnet with homogeneous dispersion of magnetic powder particles was achieved, and the weight percentage of magnetic powder in the SU8 photoresist was 41.8%. The remanent magnetization of micromagnets was 42 emu/g, the coercivity was 6895 Oe, and the maximum surface magnetic field strength was 1.3 mT after magnetization in a 2 T uniform magnetic field. Finally, the micromagnet array was utilized in a cantilever beam micro-actuator, which could drive the cantilever beam and exhibit an excellent linearity.