TMR Design Methodology for SPin-Transfer Torque RAM (SPRAM) with Nonvolatile and SRAM Compatible Operations

We propose a tunnel magneto resistance (TMR) design methodology for SPRAM that takes into account the disturbances during read operations and the data retention periods. We have clarified that the thermal stability factor (E/k_BT) of TMR must be higher than 64 to ensure a 10-year data retention and a continual non-destructive read-operation. Moreover, the thick synthetic ferromagnetic free layer with Fe-rich CoFeB can achieve a E/k_BT of 64 while maintaining a low write cell current of less than 400 muA/cell with a 100 times 160 nm² TMR.