Low resistance magnetic tunnel junctions with MgO wedge barrier

Abstract

We investigated the dependence of tunnel magnetoresistance (TMR), the resistance area (RA) product, crystallographic structure, the interlayer exchange coupling (IEC) and the coercive (Hc) fields in Co40Fe40B20/MgO/Co40Fe40B20 exchange biased spin valves on the Ar partial pressure, in the range from 1 mTorr to 15 mTorr, during the MgO sputtering. For all the metallic layers a linear dynamic deposition (LDD) with a constant wafer velocity was used, whereas for the MgO deposition a LDD wedge technology with gradient velocity. The crystallographic texture of MgO(001), IEC and Hc fields, TMR and RA significantly depend on the Ar partial pressure. We found that high Ar partial pressure (above 5.6 mTorr) resulted in weaker (001) texture, lower interplanar distances of the MgO barrier and higher IEC field. Low Ar partial pressure gives smoother MgO surfaces and provides good barrier quality which results in higher TMR and RA values