Kinetics of pinhole nucleation and growth in magnetic tunnel junctions

Tunnel junctions with different pinhole probabilities were obtained by varying natural oxidation condition. In pinhole-free junctions, the observed abrupt changes in magnetoresistance and junction resistance with increasing bias current are the signature of dielectric breakdown, and are attributed to the process of pinhole nucleation. On the contrary, low RA junctions show gradual changes in magnetoresistance and junction resistance with voltage, indicating the absence of pinhole nucleation, but only the process of pinhole growth starting from the inherent pinholes. Experimentally, the activation energy of pinhole growth (EG∼0.3 eV) is found to be much lower than that of pinhole nucleation (EN∼0.6eV), which explains the easy breakdown behavior observed in low RA junctions.