Thermally stable, low saturation field, low hysteresis, high GMR CoFe/Cu multilayers

In order to integrate giant magnetoresistive (GMR) devices with integrated circuit (IC) technology for sensors, annealing at a minimum temperature of 285°C for a few hours is required after GMR deposition to eliminate the radiation damage in transistors. A much longer term thermal stability is necessary for the integrated devices to operate at well above room temperatures. Multilayers of Ta-NiFeCo-[CoFe/Cu]₉-CoFe-Ta were found to have high GMR value, low saturation field, relatively low hysteresis and good thermal stability, and therefore have high potential for this application. These multilayers were r.f. sputter deposited on Si wafers coated with Si₃N₄. GMR value increased from a low as-deposited value of 15% to as high as 20% after annealing at 285°C. Annealing at a higher temperature of 325°C either increases or decreases the GMR value profoundly from the as-deposited values, depending on the CoFe layer thicknesses in the multilayers. Other properties such as sheet resistance and hysteresis are much less sensitive with these annealings. In order to optimize the performance of integrated GMR devices, the annealing effects have to be considered in designing starting materials