ECC-Less Multi-Level SRAM Physically Unclonable Function and 127% PUF-to-Memory Capacity Ratio with No Bitcell Modification in 28nm.

A multi-level (2 bits/bitcell) SRAM PUF is introduced to uniquely enable ECC-less operation with PUF capacity exceeding storage capacity at no cell modification. The first PUF bit is generated from steady-state post-reset bitcell value with > 4X higher stability than conventional power-up. The second is simultaneously extracted from the transient response. Above-storage capacity and improved stability eliminate ECC down to the SRAM $V_{min}(0.6V)$ at 75-fJ/bit energy and 3.3% area overhead in 28 nm.