Micromachining and micro-magnetization of Pr-Fe-B magnets fabricated using pulsed laser deposition for MEMS applications

Abstract

For MEMS actuators that use permanent magnets, such as micro linear motors, micromachining and micro-magnetization of the magnets are needed in order to enhance and concentrate the magnetic field. This paper examines these processing technologies for magnets fabricated by pulsed laser deposition (PLD magnets). Magnets of this type can be more than a hundred microns thick, which makes them suitable for high power MEMS actuators. For the micromachining, we utilized molds with micro-grooves. These were filled with magnetic material deposited using Pr2.0Fe14B target, and then polished to decrease the surface roughness of the magnets to a few tens of μm. As a result, a linear array of magnets, each 100μm wide and 50μm high, was realized. For the micro-magnetization, partial magnetization reversal due to weakening of the coercivity as a result of laser heating while applying an external magnetic field was examined. To limit the magnetization reversal to the irradiated parts, heat conduction to the non-irradiated parts was restricted by using a thermally insulating glass mold, which was fabricated by micromachining. As a result, micro-magnetized magnets with a pole pitch of 200μm were realized. The average measured magnetic flux density at a distance of 100μm from the surface of the magnets was 43mT (p-p), which corresponds to 88% of the value obtained by simulation.