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In this paper, we present a deep subthreshold 6-T SRAM, which was fabricated in an industrial 0.13 mum CMOS technology. We first use detailed simulations to explore the challenges of ultra-low-voltage memory design with a specific emphasis on the implications of variability. We then propose a single-ended 6-T SRAM design with a gated-feedback write-assist that remains robust deep in the subthreshold regime. Measurements of a test chip show that the proposed memory architecture functions from 1.2 V down to 193 mV and provides a 36% improvement in energy consumption over the previously proposed multiplexer-based subthreshold SRAM designs while using only half the area. Adjustable footers and headers are introduced, as well as body bias techniques to extend voltage scaling limits.
Date of Publication: Oct. 2008