S2RAM PUF: An Ultra-low Power Subthreshold SRAM PUF with Zero Bit Error Rate

The reliability of physical unclonable function (PUF) has become the biggest challenge for key generation. Existing reliability improvement technologies incur high hardware overhead or testing costs. This paper proposes S2RAM-PUF, a novel, highly reliable and energy-efficient subthreshold SRAM PUF fabricated in 65nm process, with zero bit error rate (BER) across all voltage/temperature corners from 0.5V to 0.8V and from -40°C to 120°C. The 20480 bits generated by the fabricated 5 S2RAM PUF chips pass the NIST 800-22 randomness test and exhibit almost ideal uniqueness with a mean inter-die hamming distance of 0.5007. The total energy per bit is as low as 3.12fJ at 0.5V supply voltage. Both stabilization BER and energy outperform the two state-of-the-art SRAM-type PUFs reported in JSSC 2020 and 2021.