Temperature stability of Co/Al2O3/Co junctions

The temperature stability of magnetic tunnel junctions is an important requirement for the fabrication of magnetic memory devices and the integration in the semiconductor process technology. We have investigated the temperature evolution of the tunneling magnetoresistance (TMR) and the structural properties by isochronal annealing experiments up to 750 K. The magnetically hard electrode of the junction consists of an artificial antiferromagnet Co/Cu/Co, the soft electrode of a Co/Fe bilayer. The tunnel barriers are formed by plasma oxidized Al. The tunnel junctions have TMR signals up to 22% at room temperature. Besides a small increase of the TMR signal after annealing up to 480 K, a first decrease at 530 K and a breakdown beyond 600 K are found. This behavior can be attributed to structural changes of the junctions. Auger depth profiles show an unaltered Al2O3 barrier up to 600 K, but the beginning of interdiffusion processes within the magnetic electrodes already at 540 K and above.