Analysis of breakdown in ferromagnetic tunnel junctions

Due to their very thin tunnel barrier layer, magnetic tunnel junctions show dielectric breakdown at voltages of the order of 1 V. At the moment of bre akdown, a highly conductive short is formed in the barrier and is visible a s a hot spot. The breakdown effect is investigated by means of voltage ramp experiments on a series of nominally identical Co/Al2O3/Co tunnel junction s. The results are described in terms of a voltage dependent breakdown prob ability, and are further analyzed within the framework of a general model f or the breakdown probability in dielectric materials, within which it is as sumed that at any time the breakdown probability is independent of the (pos sibly time-dependent) voltage that has been previously applied. The experim ental data can be described by several specific forms of the voltage breakd own probability function. A comparison with the models commonly used for de scribing thin film SiO2 breakdown is given, as well as suggestions for futu re experiments. (C) 1999 American Institute of Physics. [S0021-8979(99)0531 9-0].