A noise tolerant cache design to reduce gate and sub-threshold leakage in the nanometer regime

Abstract

Scaling devices while maintaining reasonable short channel immunity requires gate oxide thickness of less than 20 /spl Aring/ for CMOS devices beyond the 70 nm technology node. Low oxide thickness gives rise to considerable direct tunneling current (gate leakage). Power dissipation in large caches is dominated by the gate and sub-threshold leakage current. This paper proposes a novel cache that has high noise immunity with improved leakage power. For every bank of SRAM cells, this technique requires an extra diode in parallel with a gated-ground transistor connected between the source of NMOS transistors and ground in SRAM cells. The row decoder itself can be used to control the extra gated-ground transistor. Our simulation results on a 70 nm process (Berkeley Predictive Technology Model augmented with our gate leakage model) show 39.2% reduction in consumed energy (leakage plus dynamic) in L1 cache and 59.4% reduction in L2 cache energy with less than 2.5% impact on execution time. The technique is applicable to data and instruction caches as well as different levels of cache hierarchy such as the L1, L2, or L3 caches.