Self-Referenced Single-Ended Resistance Monitoring Write Termination Scheme for STT-RAM Write Energy Reduction

Abstract

Essential design requirements for a sense amplifier (SA) used in the resistance monitoring write termination (RM-WT) scheme are suggested to reduce the write energy of spin-transfer-torque random access memory (STT-RAM) while achieving a write pass yield comparable to that of a conventional write operation. In addition, a self-referenced single-ended RM-WT (SS-RM-WT) scheme is proposed. To reduce the offset voltage, a single-ended sensing circuit (SE-SC) is used in the SA. A data-aware input voltage-transfer method is also adopted in the SE-SC to maximize the input voltage difference. By adopting a capacitor between the output of the SE-SC and the input of an inverter generating a logical output used for the write termination, the conflict between maintaining and changing the output of the SE-SC is resolved. The simulation results using the industry-compatible 65-nm technology HSPICE model parameters show that the proposed SS-RM-WT scheme achieves a 44% write energy saving on average without increasing the write error rate. Area overhead is only 11.8% for a 256-kb STT-RAM array, whereas that of the previous self-referenced RM-WT schemes is up to 42.5%.