Compensated Orthogonal Anisotropy Toggle-MRAM

Magnetoresistance Random Access Memory (MRAM) is an emerging memory technology that stores information using the magnetic polarity of a thin ferromagnetic layer. MRAM cells have many potential advantages. They are non-volatile, and can be as fast and dense as DRAM cells. Further, they can be implemented above an active silicon substrate as part of a single chip in the same way as DRAM cells. One of the most important unsolved problems has been the relatively small operating field margin due to the severe requirements for the accuracy of the magnetic and structural parameters. Recent proposal of toggle-MRAM by Savchenko, et al1, in which the memory element is composed of a synthetic antiferromagnet, has attracted worldwide attention. However, it turns out that a much stronger magnetic field is necessary for its operation as compared to the conventional switching operation. We have designed a new scheme of toggle-MRAM element, in which the two anisotropy axes (intrinsic and shape) are orthogonally aligned to compensate each other (See the figure.). Such a switching element can be operated at much lower fields, compatible with the switching of ordinary MRAM elements, while maintaining the advantage of large field margin inherent to toggle-MRAM.

1. L. Savtchenko, et al., US Patent, 6, 545,906 B1 (2003).
2. S.-Y. Wang and H. Fujiwara, J. Appl. Phys. Vol. 98, 024510-1-7 (2005).