The time-dependent dielectric breakdown of Co/Al2O3/Co(-Fe) magnetic tunnel junctions is investigated. At voltages larger than 1.2 V, almost immediate breakdown of the junction is observed, leading to a decreased (magneto)resistance. The shorts, which are local hot spots, were visualized by making use of a liquid crystal film on top of the junction. The breakdown voltages of a series of nominally identical tunnel junctions measured in a voltage-ramp experiment are shown to increase with increasing ramp speed. The results are analyzed in the framework of several models for the voltage dependent breakdown probability.
Oepts, W., Verhagen, H. J., Jonge, de, W. J. M., & Coehoorn, R. (1998). Dielectric breakdown of ferromagnetic tunnel junctions. Applied Physics Letters, 73(16), 2363-2365. https://doi.org/10.1063/1.122462