Large Area and Low Aspect Ratio Linear Magnetic Tunnel Junctions With a Soft-Pinned Sensing Layer

Large area MTJs with linear response and very larger sensitivities are needed to fulfill the requirements for the detection of pT/Hz(0.5) magnetic fields at low frequency and room temperature. MTJ stacks with soft-pinned sensing layers have been developed and the stack was optimized, providing a tunable soft-pinning field over a large range of values. Sensitivities corresponding to resistance changes of up to 7%/Oe are obtained in patterned MTJs with areas of 20 x 20 mu m(2) starting from films with high sensitivity soft-pinned layers made from 3.0 Co-40 Fe-40 B-20/0.21 Ta/8.0 Ni-81 Fe-19/8.0 Ir-20 Mn-80.