Noise of MgO-based magnetic tunnel junctions

摘要

Low-frequency noise has been measured in magnetic tunnel junctions with MgO barriers and magnetoresistance values up to 235%. We present here the noise for different degrees of crystallization and CoFeB/MgO interface quality depending on the annealing temperature. For optimized annealing temperature, an extremely low 1//noise, compared to magnetic junctions with Al_2O_3 barriers, has been observed. The origin of the low-frequency noise can be explained in terms of localized charge traps with the MgO barriers. Results for very thin CoFeB are presented in the second part as a function of temperature. Despite the absence of coercivity at room temperature for thinner free-layer structures, an important increase of H_c appears under 180 K. Meanwhile, the random telegraph noise present at room temperature is suppressed due to magnetic domains freezing. These results are discussed in view of various sensors applications of MgO-MTJ, giving advantages and drawbacks in terms of signal-to-noise ratio with respect to the operating temperature.