A 215-F² Bistable Physically Unclonable Function With an ACF of <0.005 and a Native Bit Instability of 2.05% in 65-nm CMOS Process

Abstract

This article presents a novel class of bistable physically unclonable functions (PUFs) for security-oriented applications. The traditional cross-coupled bistable PUF cell is divided into P-net and N-net, wherein the P-net (N-net) multiplexing acts as the shared head (foot), and the N-net (P-net) duplicating multiple acts as the PUF cell. The proposed PUF was fabricated in a Taiwan Semiconductor Manufacturing Company (TSMC) 65-nm process with full-custom design. It can parallelly generate 128-bit identifications (IDs) in one clock cycle owing to the random access word-level readout framework. The measurement results show that the randomness and uniqueness of the proposed PUF are consistent with those of the state-of-the-art works. In addition, the proposed PUF has the following features: 1) the PUF cell is composed only of four nMOS transistors with a minimum feature size of 215-F2; 2) the native bit instability at the golden condition (i.e., 1.2 V, 25 °C) with 500 evaluations is only 2.05%, showing a desirable native stability against supply noise; 3) the bit-error-rate dependences of the voltage and temperature are 3.35%/V and 0.011%/°C, respectively, with the voltage varying within the range 1.0–1.4 V and the temperature varying within the range −40 °C to 125 °C; 4) an autocorrelation function of 0.0049 at a 95% confidence level is achieved and is the lowest reported value to date; and 5) the energy efficiency and throughput at the maximum operating frequency (i.e., 433 MHz) are 99.48 fJ/b and 55.5 Gb/s, respectively.