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 mu H-0(k) 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 alpha(H) = 7 x 10(-11) mu m(2).

Automated summary

Magnetoresistive sensors, using soft magnetic free layers, are popular for small footprint magnetic field detection applications. This study explores the TMR and noise performance of in-plane MTJ sensors with magnetically saturated CoFeBTa and CoFeSiB films as free layers. The results show improved magnetoresistance of 230% in CoFeBSi with superior noise characteristics, as well as different magneto-crystalline anisotropy values compared to CoFeB/Ru/NiFe.