Cross-Coupled Impedance-Based Physically Unclonable Function (PUF) With 1.06% Native Instability

This letter presents an ASIC implementation of a weak physically unclonable function (PUF) with a bimodal output distribution. The PUF, termed negative impedance-based PUF, is formed using a Wheatstone-bridge which employs a combination of positive and negative feedbacks to greatly amplify normally small mismatches due to process variation. The mismatch of the cell skews the overall output impedance to be negative or positive depending on the polarity of the mismatch between feedback paths. The PUF is fabricated in 65-nm TSMC LP process. The PUF performance was measured for supply voltages between 0.8 and 1.3 V, and temperatures ranging from 0 °C to 80 °C. Measurement results show a 1.06% native instability without the use of any digital calibration techniques.