MRAM with soft reference layer: In-stack combination of memory and logic functions

This paper describes an original concept of thermally assisted MRAM in which memory and logic functions are combined in the same stack. The memory cell is represented by a magnetic tunnel junction having an exchange biased storage layer and a soft reference layer (called sense layer), replacing the conventional pinned reference layer. The write of the storage layer is ensured by a combination of heating pulses and magnetic stray fields created by the soft reference layer. The read is performed in a self-referenced manner by measuring the resistance variation associated to a field variation. This makes these memories much more tolerant to cell to cell variability. In addition, this stack intrinsically performs both a storage function and a comparison (XOR) function. This device called a Magnetic Logic Unit (MLU™) is particularly suited for security applications and Content Addressable Memories.