Reduction of interlayer coupling in bottom synthetic spin valves through a gas exposure process

Abstract

The magnetoresistance (MR) ratio of spin valves can be improved by reducing the thickness of the nonmagnetic interlayer, such as Cu, due to not only reducing the shunt, but also increasing the probability of electrons scattered through the Cu. However, at small thickness, interlayer coupling between the free and pinned layer is increased, which makes it difficult to control the bias point. The minimum thickness of the interlayer Cu was thereby limited to around 3 nm. On the other hand, it is reported that the ferromagnetic interlayer coupling that arises from the film roughness can be reduced by controlling the residual gas inside the deposition chamber. The same effect can also be achieved by exposing the wafer into an oxygen gas atmosphere right after the deposition of the high conductive Cu interlayer. By this method the thickness of the interlayer Cu was reduced successfully from 3.0 to 2.0 nm without increasing the interlayer coupling. As a result, the MR ratio and dRsq was improved by 12% and 48%, and showed 10% and 1.82 Ω, respectively. Furthermore, by inserting a Cu backlayer to form a spin filter spin valve structure an antiferromagnetic interlayer coupling was also observed.