Adjusting Thermal Stability in Double-Barrier MTJ for Energy Improvement in Cryogenic STT-MRAMs

TL;DR

This study demonstrates that relaxing the thermal stability of double-barrier MTJs at cryogenic temperatures significantly improves energy efficiency in STT-MRAMs, making them competitive with traditional SRAMs.

Contribution

It introduces a macrospin-based model and process calibration showing how reduced retention requirements at 77K enhance energy efficiency of DMTJ-based STT-MRAMs.

Findings

Energy-efficient memories achieved by reducing DMTJ cross-section area.

DMTJ-based STT-MRAM outperforms 6T-SRAM in energy consumption at 77K.

Relaxed retention time maintains 10-year stability at cryogenic temperatures.

Abstract

This paper investigates the impact of thermal stability relaxation in double-barrier magnetic tunnel junctions (DMTJs) for energy-efficient spin-transfer torque magnetic random access memories (STT-MRAMs) operating at the liquid nitrogen boiling point (77K). Our study is carried out through a macrospin-based Verilog-A compact model of DMTJ, along with a 65nm commercial process design kit (PDK) calibrated down to 77K under silicon measurements. Comprehensive bitcell-level electrical characterization is used to estimate the energy/latency per operation and leakage power at the memory architecture-level. As a main result of our analysis, we show that energy-efficient small-to-large embedded memories can be obtained by significantly relaxing the non-volatility requirement of DMTJ devices at room temperature (i.e., by reducing the cross-section area), while maintaining the typical 10-years retention time at cryogenic temperatures. This makes DMTJ-based STT-MRAM operating at 77K more energy-efficient than six-transistors static random-access memory (6T-SRAM) under both read and write accesses (-56% and -37% on average, respectively). Obtained results thus prove that DMTJ-based STT-MRAM with relaxed retention time is a promising alternative for the realization of reliable and energy-efficient embedded memories operating at cryogenic temperatures.