A laminated magnetic flux concentrator with low coercivity and high relative permeability for efficient flux modulation in MEMS magnetoresistive sensors

The detectivity of magnetic tunnel junction (MTJ) sensors cannot be improved further because of the existence of 1/f noise. Micro - electromechanical systems (MEMS) integrated with magnetic flux concentrators (MFCs) can be an effective approach to suppressing 1/f noise for modulating low-frequency magnetic fields. The challenge in fabricating small-sized and low-noise MTJ-MEMS hybrid magnetic sensors is associated with the production of high-performance MFCs. For the preparation of MFCs applicable to MTJ-MEMS hybrid magnetic sensors, in this research, a novel Ta/Ni77Fe14Cu5Mo4 laminated structure was adopted to decrease the coercivity of the magnetic film dozens of times. Also, through optimizing the sputtering power, a relative permeability of 3246 was attained. The simulation outcomes demonstrated that the MTJ-MEMS hybrid magnetic sensor which utilized this magnetic film had a modulation efficiency of 65.4%, and it retained a competitive edge among similar magnetic sensors. A sensor prototype was successfully developed with 400-nm- thick MFCs by optimizing the fabrication process, and the MTJ’s sensitivity was increased by 2.2 times. In comparison to low-frequency noise, the high-frequency noise of the MTJ showed a reduction in noise power spectral density by a factor of 686. MTJ sensors will be highly competitive candidates in the field of ultra-weak magnetic field detection because of these results.