Tuning the linear field range of tunnel magnetoresistive sensor with MgO capping in perpendicular pinned double-interface CoFeB/MgO structure

A double-interface CoFeB/MgO perpendicular tunnel magnetoresistance (p-TMR) structure has been proposed as a solution to improve the thermal stability of perpendicular magnetic tunnel junction (MTJ)-based devices. In this paper, we have investigated the performance of TMR film stacks by varying the thickness of the MgO cap layer. The resistance area (RA) product and TMR ratio are characterized using a current-in-plane tunneling system. Structural and physical analyses are performed using transmission electron microscopy and a superconducting quantum interference device. It is found that the sensing layer is able to exhibit a linear output and sensitivity up to 0.25% MR/Oe as the thickness of the MgO cap layer is lowered to 0.7 nm. The RA product increases as the thickness of the MgO cap layer decreases under 0.8 nm, which is attributed to oxidization of the CoFeB layer. This research provides a valuable direction to the optimization of double-interface CoFeB/MgO p-TMR and the sensor design in terms of linear magnetic field range and sensor RA product target for sensor applications.