A Multimode Configurable Physically Unclonable Function With Bit-Instability-Screening and Power-Gating Strategies

Abstract

This study presents a technique for designing a multimode configurable weak physically unclonable function (PUF) for security-key generation. The PUF cell is based on the maximum gain point deviations of bias-voltage-controlled inverters. By implementing a preselection strategy, the proposed PUF can simultaneously expose all unstable cells under normal voltage and temperature. Owing to the configurable bias circuit, the PUF cell can be biased at three operating modes, namely, traditional inverter (INV), current-starved inverter (CSI), and power gating (PG). The measurement results from a 65-nm prototype show that the proposed PUF has the following outstanding features: 1) it has a compact cell layout with a minimum feature size of 966 F2; 2) an autocorrelation function of 0.0099 is achieved; and 3) all unstable cells can be eliminated using a preselection procedure, which can drastically reduce the energy and area costs for error correction. In addition, in the CSI mode, the proposed PUF (standard voltage) has maximum frequency and throughput of 714 MHz and 45.7 Gb/s, respectively. Meanwhile, under the INV mode, the worst native bit error rate (low voltage) for 5000 evaluations is only 0.33%, indicating a desirable instability against voltage and temperature variations with a sensitivity coefficient of 1.85%/V and 0.018%/°C, respectively. Moreover, the measured energy efficiency at 0.6 V is 6.83 fJ/bit. Finally, under the PG mode, the standby powers at 0.6 and 1.2 V are only 18 and 86 nW, respectively.