Aging effects on ring-oscillator-based physical unclonable functions on FPGAs

On-Chip Physical Unclonable Functions (PUFs) are a powerful way to generate intrinsic keys by using production tolerances. Robustness of the PUF against reversible environmental changes and irreversible aging effects is crucial for its reliability. The influence of environmental changes is already studied in depth, however, there is still limited research on aging effects. We performed accelerated aging tests on 28 nm Xilinx Zynq FPGAs and compared the impact to reversible environmental fluctuations. Designs with different types of logical stress were used to amplify the effects of various aging mechanisms. The impact of accelerated life conditions on the frequency of different ring oscillator PUFs was measured and analyzed. It was shown that the aging effect is dramatically accelerated with higher temperatures and voltages. The reliability of the PUFs without error correction was still at around 96% after an effective accelerated aging duration of around 31 years. This confirmed that most of the PUFs age similarly and the variations are compensated by using differential measurements. The length of the ring oscillator had no severe influence on its reliability. Our investigations showed that aging effects reduce the reliability in the same order of magnitude as environmental variations.