Temperature, Voltage, and Aging Effects in Ring Oscillator Physical Unclonable Function

Abstract

Physical unclonable functions (PUFs) are security features that are based on process variations that occur during silicon chip fabrication. As PUFs are dependent on process variations, they need to be robust against reversible and irreversible temporal variabilities. In this paper, we present experimental results showing temporal variability in 4, 5, and 7-stage ring oscillator PUFs (ROPUFs). The reversible temporal variabilities are studied based on voltage and temperature variations, and the irreversible temporal variabilities are studied based on accelerated aging. Our results show that ROPUFs are sensitive to temperature and voltage variations regardless of the number of RO stages used. It is also observed that the aging, temperature, and voltage variation effects are observed to be uniformly distributed throughout the chip. This is evidenced by noting uniform changes in the RO frequency. Our results also show that most of the bit flips occur when the frequency difference in the RO pairs is low. This leads us to the conclusion that RO comparison pairs that pass high frequency threshold should be filtered to reduce temporal variabilities effect on the ROPUF. The experimental results also show that the 3-stage ROPUF has the lowest percentage of bit flip occurrences and the highest number of RO comparison pairs that pass high frequency threshold.