Junction area dependence of breakdown characteristics in magnetic tunnel junctions

Abstract

Breakdown characteristics of the magnetic tunnel junctions (MTJ) with different junction areas of S=200 μm2 and S=0.5 μm2 are investigated under constant voltage stress. The breakdown process is found to be quite different for the two junction areas. For the large junctions with S=200 μm2, magnetoresistance (MR) ratio decreases gradually with increasing time of constant voltage stress and lasts for 10–30 min. The low frequency 1/f noise power also increases with increasing stress time due to the Johnson and shot noises, caused by current flowing through ohmic shorts or pinholes across tunnel barrier. Meanwhile, the junctions with S=0.5 μm2 show abrupt junction breakdown after stress time of 1–7 h. There is no significant change in both MR ratio and its bias dependence during the voltage stress. In particular, soft-breakdown events are observed before total breakdown occurs. The junction breakdown of small junction area is of intrinsic nature of the junction while the one of large junction area is due to extrinsic factors.