A 0.28-0.8V 320 fW D-latch for sub-VT memories in 65 nm CMOS

The design of an ultra-low-leakage latch, suitable for subthreshold standard-cell based memories in 65nm CMOS is presented. Various latch architectures are compared in terms of leakage, area and speed. The most leakage-efficient architecture is optimized by transistor stacking and channel length stretching. The final design is supplemented with a 3-state output buffer to provide low-leakage read functionality in memory applications. Silicon measurements confirm simulation results including the reliability analysis based on Monte-Carlo simulations. The latch is fully functional at 280mV and retains data down to a supply voltage of 220mV, consuming as little as 230fW leakage power.