Oppositely Biased Multibit Cells for Toggle Magnetic Random Access Memory

A new type of multibit cell for toggle type MRAM is presented. The dual-bit cell stack consists of two conventional toggle MRAM cells connected in series. These cells have the same cell geometry, anisotropy, and pinned directions but have opposite magnetic bias along the anisotropy axis directions. These oppositely biasing fields shift the write field switching window of the two cells in opposite directions along the anisotropy axis and enable the dual-bit cells to be selectively toggled. The calculated write switching current margins for the multibit cell with respect to the design and material parameters are included. The write current margin is found to be similar to the single biased low write current MRAM case. This oppositely bias scheme can be combined with the earlier multibit cell of distinct anisotropy axes approach to further enhance the density of the MRAM. This new scheme doubles the multicell bit capacity and reduces the power consumption without adding the photo-patterning steps