A technique to transform 6T-SRAM arrays into robust analog PUF with minimal overhead

Physically unclonable function (PUF) is one of the critical security primitives for key generation and storage. The key challenge in building a PUF is to achieve high robustness against noise, temperature/supply voltage (VDD) variations and device aging with low cost. This paper presents a technique to transform a pre-existing SRAM array into an analog PUF by configuring the access transistors in a 6T-SRAM bitcell into a pair of threshold voltage (Vth) sensors and comparing their outputs. The proposed analog PUF circuit achieves significantly better robustness than conventional SRAM-based PUFs using reset states while maintaining the benefit of hardware reuse: low area overhead. Test chips are prototyped in a 65nm CMOS to verify the randomness, uniqueness, and robustness of the proposed design.