A new multilayered structure for multilevel magnetoresistive random access memory (MRAM) cell

摘要

It is common practice to use two magnetic layers separated by a non-magnetic layer such as copper for the spin valve system. In this work, three magnetic layers (NiFe, NiFe/Co, and Co) are used to form a spin valve and its magnetic properties are characterized. Due to the difference in the coercive field of the three magnetic layers, two plateaus can be obtained in M-H and R-H curves. Each plateau plays as a recording level. According to the external magnetic fields, four distinguishable resistance states can be identified. The optimum preparative condition for the well defined four states have turned out to be NiFe(6 nm)/Cu(2 nm)/NiFe(1.5 nm)/Co(4.5 nm)/Cu(2 nm)/Co(3 nm), where the multilevel MRAM is proved to be realized.