Evolution of the dielectric breakdown in Co/Al2O3/Co junctions by annealing

The temperature and dielectric stability of magnetic tunnel junctions are important requirements for magnetic memory devices and their integration in the semiconductor process technology. We have investigated the changes of the tunneling magnetoresistance (TMR), the barrier properties (height, thickness, and asymmetry) and the dielectric stability upon isochronal annealing up to 410 degreesC in Co/Al2O3/Co junctions with an artificial antiferromagnet as a pinning layer. Besides a small decrease of the TMR signal after annealing up to 230 degreesC, a strong decrease between 300 and 350 degreesC is found. According to Auger and transmission electron microscopy investigations, this decrease is mainly due to interdiffusion of the metallic layers. The dielectric breakdown is characterized by voltage ramp experiments. The size-averaged breakdown voltage improves from 1.35 V for the as prepared junctions to 1.55 V by annealing at 300 degreesC. At higher temperatures the breakdown voltage decreases strongly to 0.8 V (at 380 degreesC). Simultaneously, the typical breakdown process changes from few sudden current jumps to a large number of small steps. The breakdown properties are discussed within a statistical model and related to structural changes of the barrier. (C) 2001 American Institute of Physics.