STT-MRAM Technology For Energy-Efficient Cryogenic Memory Applications

This work explores non-volatile (NV) embedded memories implemented by spin-transfer torque magnetic random access memories (STT-MRAMs). Our designs are based on state-of-the-art perpendicular magnetic tunnel junctions (MTJs) along with a commercial 65 nm planar CMOS Bulk technology node, both operating at the liquid nitrogen temperature, 77 K. We evaluate the impact of cooling down to 77 K of the STT-MRAMs based on single- and double-barrier MTJ (SMTJ and DMTJ), and DMTJ with the relaxed non-volatility. All NV designs were benchmarked against the six-transistor SRAM (6T-SRAM) baseline. Simulation analysis relies on a 512 kB cache memory operating at 77 K. Overall, results show that the implementation of STT-MRAMs with DMTJ devices, and in particular when using the non-volatility approach by reducing the cross-section area, excel in terms of energy consumption, leading to energy savings for write/read access of about 35%/54%. This saving is obtained while also dissipating less leakage power and requiring a smaller bitcell footprint. Moreover, it presents reduced write latency overhead (as much as 1.9× lower), at the expense of increased read latency and reduced sensing margins of about 1.8× and 88%, respectively. The results suggest that STT-MRAM technology can be a solid alternative for energy-efficient cryogenic memory applications.