Reliability of MgO in magnetic tunnel junctions formed by MgO sputtering and Mg oxidation

The film properties and breakdown characteristics of the MgO films formed via radio frequency (RF) sputtering and Mg oxidation in the CoFeB/MgO/CoFeB structure were evaluated. The properties of the RF-MgO and Mg-oxidation films were improved by annealing. The breakdown of both films depended on the stress voltage. Uniform MgO could not be formed by oxidation alone; the required temperature to improve the breakdown characteristics of Mg-oxidation film is approximately 50°C higher than that of RF-MgO film, and the initial failure was remained after the annealing at 350° C in the Mg-oxidation film.