Preselection Methods to Achieve Very Low BER in SRAM-Based PUFs - A Tutorial

The most prevalent industrial PUFs (physical unclonable functions) utilize SRAM-based designs. Bit stability is one of the fundamental problems in PUF design. PUF circuits, which rely on silicon manufacturing mismatches to produce a random key, are vulnerable to cases where the mismatch is insufficient and noise affects the PUF response, rendering it unstable. This brief provides a tutorial about SRAM-based PUFs stable bits preselection, utilizing an embedded tilt test. This method is more efficient than existing error correction codes in terms of power, area and latency. During the test, external, controlled mismatch, tilts the PUF cells against their manufactured mismatch and cells that retain their response are considered stable. In this tutorial, the preselection method is explained, implementation examples are presented, and a method to further exploit the test to obtain more uncorrelated stable bits from the existing PUF structure is introduced.