Double-pinned magnetic tunnel junction sensors with spin-valve-like sensing layers

MgO magnetic tunnel junction (MTJ) sensors with spin-valve-like sensing layers of Ir₂₂Mn₇₈ (6)/Ni₈₀Fe₂₀ (t_NiFe = 20–70)/Ru (0.9)/Co₄₀Fe₄₀B₂₀ (3) (unit: nm) have been fabricated. A linear field dependence of magnetoresistance for these MTJ sensors was obtained by carrying out a two-step field annealing process. The sensitivity and linear field range can be tuned by varying the thickness of NiFe layer and annealing temperature, and a high sensitivity of 37%/mT has been achieved in the MTJ sensors with 70 nm NiFe at the optimum annealing temperature of 230 °C. Combining the spin-valve-like sensing structure and a soft magnetic NiFe layer, MTJ sensors with relatively wide field sensing range have been achieved and could be promising for showing high sensitivity magnetic field sensing applications