DRAM Physically Unclonable Function (PUF) Using Dual Word-Line Activated Twin-Cells

Abstract

Physically unclonable function (PUF) generates a unique fingerprint or root of trust using the inherent randomness introduced during manufacturing. PUF outputs requires to be unique, random, robust, and unclonable. Dynamic random access memory (DRAM)-based PUFs are attractive due to their high density and randomness, achieved by controlling critical timings parameters, including t(RCD), t(RP), and t(REF). Traditional DRAM PUFs use a single word-line (WL) to select individual cells connected to a bit-line (BL), generating random outputs through "absolute" mismatches in properties such as cell capacitance, leakage current, and charge redistribution timings. In this brief, we present a novel twin-cell DRAM PUF that employs "differential" mismatches between activated cells. Dual WLs in this design activated both twin-cells connected to the BL and bit- line bar (BLb). Leakage currents through the access transistors discharged the precharged cells, and the residual charges in the cell capacitances were redistributed to the BL capacitances following the discharge period. The sense amplifier amplified the relative mismatches between the twin-cells to generate the PUF output. The PUF was fabricated using a 28 nm complementary metal oxide semiconductor (CMOS) process. It operates at a nominal voltage of 1 V. It demonstrated 49.5% uniformity and 98.51% reliability under nominal voltage and temperature. The inter-chip Hamming distance (HD) was 45.91%, while the inter-WL HD and inter-PUF HD were 50.19% and 49.98%, respectively.