Temperature Aware Adaptations for Improved Read Reliability in STT-MRAM Memory Subsystem

Abstract

Spin-transfer torque magneto-resistive random-access memory (STT-MRAM) is an exciting new emerging technology, being considered as a strong candidate to fill the gaps in the existing memory hierarchy between DRAM and the secondary memory. STT-MRAM has adequate endurance. However, unresolved write switching and read reliability issues still exist at the functional operating temperature corners. One biggest challenge is that the read bit error rate (RBER) is not at an acceptable level for system reliability across the wide operating temperature range. We present an STT-MRAM memory subsystem that is fully compatible with existing DDR-based DIMM designs and evaluate read disturb and read sense bit-error rate (BER) under various operating temperature conditions. We propose temperature aware adaptive techniques for reliable reads at the rank level. The proposed temperature adaptation technique improves overall reliability of the DDR4 STT-MRAM-based memory subsystem with an optimal read current considering an acceptable 64-byte cacheline BER. Our full system simulations show $1000\times $ order of improvements toward a cell raw read disturb BER along with 5% reduction in memory power and less than 1% impact on overall system performance.