A Reconfigurable SRAM CRP PUF with High Reliability and Randomness

This paper presents a novel reconfigurable SRAM CRP PUF that can achieve high reliability and randomness. In conventional reconfigurable SRAM CRP PUFs, imprecise timing control can produce a biased response output, which is typically attributed to mismatches in the connection of input control signals to the two inverter arrays in the layout floorplan. We propose a timing control scheme along with the addition of an adjunct NMOS transistor to address this issue. This eliminates the connection mismatches for the challenge and word-line inputs to the two inverter arrays. Furthermore, we employ symmetric layout techniques to achieve the randomness of response output. The symmetric arrangement of the two inverter arrays maximizes the inherent random output characteristics derived from process variation. The pre-charge input signal is symmetrically connected to each array to prevent delay mismatches. A 16 × 9-bit reconfigurable PUF array is fabricated by using a 180 nm CMOS process, with a PUF cell area of 1.2 × 104 F2/bit. The experimental results demonstrate an inter Hamming distance of 0.4949 across 40 chips and an intra Hamming distance of 0.0167 for a single chip in 5000 trials. The measured worst bit error rate (BER) is 4.86% at the nominal point (1.8 V, 25 °C). The proposed prototype exhibits good reliability and randomness, as well as a small silicon area when compared to the conventional SRAM CRP PUFs.