A novel slope detection technique for robust STTRAM sensing

Abstract

Spin-Torque-Transfer RAM (STTRAM) is a promising technology for high density on-chip cache due to low standby power and high speed. However, the process variation of magnetic tunnel junction (MTJ) and access transistor poses serious challenge to sensing. Nondestructive sensing suffers from reference resistance variation whereas destructive sensing suffers from failures due to unoptimized selection of data and reference currents. We propose a novel slope detection technique to exploit MTJ resistance switching from high to low state using low-overhead sample-and-hold circuit. The proposed sensing technique is destructive in nature and can be combined with double sampling for improved robustness. Simulation results reveal <;0.12% failure under process variation using single sampling (at 0.2% area overhead) and <;0.08% failures with double sampling (at 0.6% area overhead). The overall sense time is found to be 6.8ns.