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In this paper, we propose a methodology to model and optimize FinFET devices for robust and low-power SRAMs. We propose to optimize the gate sidewall offset spacer thickness to simultaneously minimize leakage current and drain capacitance to on-current ratio in FinFET. With the source/drain extension doping controlled at the outer edges of the spacer, the thickness of the spacer determines the channel length. Optimization reduces the sensitivity of the device threshold voltage to the fluctuations in silicon thickness (by 32%) and gate length (by 73%). Our analysis shows that optimization of spacer thickness results in 65% reduction in SRAM cell leakage and improves cell read-failure probability (by 200 X) compared to conventional FinFET SRAM. Access time of an SRAM cell designed with optimized devices is comparable to conventional SRAM. We also compared the optimized-spacer-thickness SRAM cell with one designed using longer gate length and minimum-spacer-thickness transistors. The long-channel-device-based SRAM cell is marginally robust than optimized SRAM; however, increased gate-edge direct-tunneling leakage and parasitic capacitances degrade the power consumption and access time.
Date of Publication: June 2007