A 4-fJ/b Delay-Hardened Physically Unclonable Function Circuit With Selective Bit Destabilization in 14-nm Trigate CMOS

Abstract

This paper describes a full-entropy 128-b key generation platform based on a 1024-b hybrid physically unclonable function (PUF) array, fabricated in 14-nm trigate high-k/metal-gate CMOS. Delay-hardened hybrid PUF cells use differential clock delay insertion to favor circuit evaluation in the desired direction while leveraging burn-in-induced aging for selective bit destabilization enabling quick identification and masking of unstable cells, and subsequent temporal-majority-voting with soft dark-bit masking to reduce PUF bit error by 3.9 times to 1.45% resulting in ~5 ppb failure probability. A stable full-entropy 128-b key is finally generated from the 1024 raw PUF bits using BCH error correction and AES-CBC-based entropy extraction. An all-digital design with compact PUF cell layout occupying $1.84~\mu \text{m}^{2}$ achieves: 1) 4-fJ/b energy-efficiency with 3-μW leakage at 0.65 V, 70 °C; 2) peak operating frequency of 1 GHz resulting in 1.2-μs key generation latency; 3) robust operation with stable key generation across 0.55–0.75 V, and 25 °C–110 °C; 4) 14 times separation between intra/inter-PUF hamming distances with 0.99993 entropy ensuring cryptographic quality randomness and uniqueness; 5) 48% higher PUF stability with long-term aging by leveraging transistor degradation to reinforce favorable cell bias; and 6) resiliency to power cycling attacks with common centroid clock routing measured from 49.5% hamming distance between array’s evaluation and wake-up states.