Design Considerations for Reliable OxRAM-Based Non-Volatile Flip-Flops in 28nm FD-SOI Technology

This paper investigates the design architectures for reliable high-yield low operating voltage non-volatile flip-flops (NVFF) for zero-leakage and instantaneously-on ultra-low power applications in scaled CMOS technologies. A reliable thin-gate oxide NVFF, integrating OxRAM current-based storing and restoring solutions is designed and analyzed in 28nm FD-SOI. The proposed class of NVFF designs has been optimized for optimal OxRAM programming conditions that improve endurance and minimize programming power, while ensuring high yield. The OxRAM device silicon measurements show that a low programming current benefits endurance, but at the expense of a reduced memory window (ROFF/RON). Statistical analysis demonstrates that a low NVFF operating voltage in restore mode can be achieved with a narrow memory window by using the current-based restoring. In a representative design, compared to a standard FF, the non-volatility is added at the cost of less than 3% of performance and up to 3.5%-13% of active energy increase, with 108 cycles of endurance. Then compared with the data-retention FF supplied at 0.5V, NVFF reduces the sleep power consumption for standby modes longer than 0.34s for uniform Q switching (0.17s - 0.6s) Finally, the low variability of the FD-SOI technology enables 3 sigma yield restore down to 0.7V.