CoFeBX layers for MgO-based magnetic tunnel junction sensors with improved magnetoresistance and noise performance

Magnetoresistive sensors have been enthusiastically selected for applications requiring magnetic field detection with small footprint sensors. The optimisation of the sensor response includes using soft magnetic free layers, based on CoFeB and NiFe alloys. Here we report the TMR and noise performance of magnetically saturated in-plane MTJ sensors including CoFeBTa and CoFeSiB soft magnetic films as free layers (FL). Assessing magneto-crystalline anisotropy μ0Hk values of 2.1 and 0.7 mT in CoFeB 2.5 (nm)/Ru 0.2/CoFeBTa 4 and CoFeB 3/Ru 0.2/CoFeSiB 4 compared to 1.7 mT in CoFeB 2.5/Ru 0.2/NiFe 4, together with an improved magnetoresistance of 230% in CoFeBSi comparing with 170% (NiFe) with superior noise characteristics, with Hooge parameter of αH = 7 × 10−11 μm2.