Disturb robust switching astroid curve of C-shaped cell with weakly coupled synthetic antiferromagnetic layer

摘要

Magnetoresitive random access memory (MRAM) is one of a most attractive candidates for a nonvolatile RAM. However, the disturbance problem of half-selected elements is a serious issue preventing MRAM from keeping its non-volatility. The control of switching astroid curve is the key to solving this problem. The features of ideal astroid curve for MRAM are explained as follows. First, operational switching field must be small enough. Second, it should be hard for the magnetization switching to occur with large applied field on the easy or hard axis, which is an important feature for improving the disturb robustness of half-selected elements. In order to control an astroid curve, several groups proposed special shapes of magnetic free layer, which stabilize the C-type magnetic domains during switching and enhance their easy axis coercivity H{sub}c [1-3]. For example, Y. K. Ha et al. demonstrated that an asymmetric shape using the synthetic anti-ferromagnetic (SAF) free layer shows the large H{sub}c and small operating field. Our proposed shape shows above mentioned properties with two C-type magnetic domains with easy axis field. Nevertheless, these proposals are ineffective for improving disturbance problem with hard axis field. It is because their switching mechanisms are not different from typical switching mechanism of S-type magnetic domains when large field is applied on hard axis. In this paper, we propose a C-shaped cell with weakly coupled SAF (WSAF) layer, which features large H{sub}c, small operational switching field and improved robustness against the writing disturbance with large field on hard axis.