Energy-efficient cache memories using a dual-Vt 4T SRAM cell with read-assist techniques

In order to improve the energy-efficiency of cache memories, this paper presents a static random access memory (SRAM) cell composed of four transistors using dual-V_t FinFET devices. The proposed 4T SRAM cell is designed by (i) removing pull-down transistors of the standard 6T SRAM, and (ii) using low-leakage high-V_t devices for pull-up transistors and fast low-V_t devices for access transistors. This dual-V_t design simultaneously improves hold and write characteristics, but results in a destructive read operation. Accordingly, read-assist techniques are employed to ensure a non-destructive and robust read operation. A selective row address decoder is also proposed to prevent the undesired write operation in half-selected cells. The 4T SRAM cell compared with the all-single-fin 6T counterpart has a 25% smaller layout area with an aspect ratio closer to one. Furthermore, using 7nm FinFET devices with a nominal supply voltage of 0.45V, the 4T SRAM cell achieves 3.5× lower cell leakage power. Because of these features, the energy consumption of a 32KB L1 (256KB L2) cache memory using 4T SRAM cell compared with its 6T counterpart is reduced by 18% (2×), with 35% (19%) higher cache access frequency.