MgO-barrier magnetic tunnel junction sensors with both CoFeB layers pinned by IrMn have been fabricated, which show a tunneling magnetoresistance (TMR) of up to 255% at room temperature. The perpendicular configuration for magnetic field sensing is set using a two-step field annealing process. The linear TMR field range and sensitivity are tuned by inserting an ultrathin Ru layer between the upper IrMn and the top-pinned CoFeB layer. The field sensitivity reaches 26%/mT, while the noise detectivity is about 90 nT/ √Hz at 10 Hz for a 0.3 nm Ru insertion layer. The bias dependence of the noise suggests that this is a useful design for sensor applications.
Bibliographical noteFunding Information:
The authors thank H. Kurt and R. Stearrett for helpful discussions, M. Venkatesan for the SQUID measurement. The work was supported by the EU as part of FP7 NAMDIATREAM Project and by Science Foundation Ireland as part of the Nanoscale Interface and Spin Electronics (NISE) Project (10/IN1/I3002).