Technology-circuit co-design in width-quantized quasi-planar double-gate SRAM

SRAM is likely to remain the largest, leakiest and most process-sensitive circuit block on chip. FinFET, a width-quantized, quasi-planar, double-gate technology, has emerged as the most likely candidate to replace classical technologies around the 45nm node. This paper studies the impact of FinFET design choices on device and SRAM circuit metrics to understand how its unique properties can be suitably harnessed. Width-quantization limits SRAM sizing choices, while quasi-planarity allows increased cell current by increasing fin height. Conversely, the latter property can be exploited to increase V_t and/or decrease V_dd to achieve exponential leakage savings at constant access time. The authors explored both approaches to selecting the right combination of device structure, V_t and V_dd that achieves maximum stability and minimum leakage over the design space. Increasing V_t with fin height and body thickness improves stability, decreases variability and decreases source-drain leakage exponentially. But this necessitates the use of small t_ox to control short channel effect; this increases gate leakage exponentially. On the other hand, increasing V_t and decreasing V_dd allows the use of larger t_ox to maintain short-channel effect and control gate leakage; however, this worsens stability.