A Reliable Strong PUF Based on Switched-Capacitor Circuit

This paper presents a highly reliable and invasiveattack-resistant switched-capacitor (SC) strong physical unclonable function (PUF), which can offer an extremely large number of challenge-response pairs. Two symmetrical capacitor arrays that are controlled by challenges are used to realize the strong ability of SC PUF. The mismatch created by the capacitor arrays in real fabrication is sampled by an SC circuit and further amplified by a latch-styled sense amplifier. By covering the entire chip with the metallic transmission lines connected to the sampling capacitor, the PUF can resist invasive attacks. To provide highly reliable responses, a built-in self-test (BIST) strategy is also adopted. A test capacitor is embedded in the PUF circuits to automatically test the capacitance deviation of the SC circuit. Only when the capacitance deviation is large, the output of the PUF is selected for use. The proposed strong SC PUF circuit is fabricated and verified using HJ standard 0.18-μm CMOS process. Measured results show that after using the BIST strategy, the bit error rate is less than 10-9 when the ratio of the selected responses is 19.6% for the PUF instances in our test.