Toggle magnetic random access memory cells scalable to a capacity of over 100 megabits

We investigated the toggle-writing characteristics of magnetic tunnel junctions (MTJs) with minimum bit widths as narrow as 90 nm. The MTJs were fabricated using electron-beam lithography and a 0.24 mu m complementary metal-oxide semiconductor process. Here, we discuss the scalability in bit writing of toggle magnetic random access memories (MRAMs) with toggle cells consisting of two soft magnetic layers ferromagnetically coupled with synthetic antiferromagnets (2SL-FC-SAFs). The effect of the structures of 2SL-FC-SAFs on toggle writing against a reduction in bit width was examined. Taking account of the distributions of seven standard deviations, 2SL-FC-SAFs were shown to decrease the writing current to around 3 mA when a Cu yoke wire was used for writing lines, while maintaining the writing margin in both 110 and 170 nm wide MTJs. The thermal activation robustness of these cells, which was measured by the direct switching probability versus the pulse field duration, ensures 10-year retentions. These writing characteristics make toggle MRAMs with a density of over 100 megabits possible.