Keywords:Magnetic field sensor, tunnel magnetoresistance, 1/f noise
To improve the magnetic field sensing performance of CoFeB/MgO/CoFeB magnetic tunnel junction (MTJ) sensor devices, the CoFeB free layer (FL) is often laminated with soft-magnetic materials such as NiFe. However, the lamination of NiFe above/below CoFeB tends to degrade the TMR ratio because the 111 texture of NiFe propagates to the CoFeB layer. In this study, we introduced an amorphous (Co0.4Fe0.4B0.2)91Ta9 in the FL of top-pinned spin-valve MTJs, resulting in no influnce on the texture of CoFeB and thereby TMR ratios. Linear R-H curves with a negligible coercivity have been obtained by using two-step annealing technique. The low-frequency properties have been investigated. All sensors showed 1/f noise behaviors. Moreover, we achieved a detectivity as low as ~ 2 nT/Hz0.5 using a single MTJ sensor and ~ 600 pT/Hz0.5 using a Wheatstone bridge sensor.