High-Performance Thick On-chip Hard Magnets for MEMS Applications

We adopted two methods for thick on-chip hard magnets fabrication for MEMS application. (1) Dry packing of Nd₂Fe₁₄B powders. Nd₂Fe₁₄B powders were mixed with binder wax powders, then dry-packed into pre-etched trenches on silicon wafers under 10 MPa pressure and 100°C heating. An out-of-plane, in-situ magnetic field of 1000 Oe was applied during the process. (2) High pressure compression of Nd₂Fe₁₄B powders. Nd₂Fe₁₄B powders were packed into a metal mould and heated to 300°C with 850 MPa pressure applied. The sample was bonded onto the silicon chip with polyimide. The dry-packed Nd₂Fe₁₄B magnets showed a remanent out-of-plane magnetization of 330 emu/cc (B_r = 0.42 T), a coercive field of 8.6 kOe (690 kA/m) and an energy product of 2.4~2.6 MGOe (19-21 kJ/m³). It is also found that the out-of-plane magnetic field can boost the remanent magnetization in that direction. For high pressure compressed Nd₂Fe₁₄B magnets, a remanent out-of-plane magnetization of 446 emu/cc (B_r = 0.56 T), a coercive field of 9.6 kOe (770 kA/m) and an energy product of 6.4 MGOe (50.5 kJ/m³) were observed. Our demonstrated Nd₂Fe₁₄B on-chip hard magnets are compatible to MEMS fabrication process with a larger thickness of over 1mm and higher achieved energy product over published results for on-chip magnets.