Tri-Mode Independent-Gate FinFETs for Dynamic Voltage/Frequency Scalable 6T SRAMs

Abstract

In this paper, we present tri-mode independent-gate (IG) FinFETs for dynamic voltage/frequency scalable 6T SRAMs. The proposed design exploits the fact that the spacer patterning technology, used for FinFET fabrication, offers the same device footprint for two- and one-fin transistors. The access transistor is designed for operation in three on-state modes achieving simultaneous increase in the read stability and write-ability and enabling appropriate tradeoffs between read stability and access time depending on the frequency requirements. The proposed design achieves 40%-48% higher weak-write test voltage and 2%-34% lower cell write time across a range of voltages compared with a conventional FinFET-based 6T SRAM under iso-leakage. During the read operation at high workload conditions (VDD = 0.7 V), 8% improvement in read static noise margin (SNM) is achieved with only 7% access time penalty. During the read operation at low workload conditions, 54%-75% improvement in the read SNM enables low voltage operation under process variations. The proposed IG FinFET SRAM achieves 125-136 mV lower VMIN across different global process corners at the cost of 15-mV higher retention VMIN. Iso-leakage comparison of the proposed technique with the previously proposed IG FinFET 6T SRAM is also performed. An increase in the cell area by 35% is observed compared to the minimum-sized conventional FinFET SRAM. However, there is no cell area penalty compared to the previously proposed IG FinFET SRAM.