Physically Unclonable Function Utilizing Stochastic Indirect Exchange Interaction

In hardware‐based security, physically unclonable function (PUF) has emerged as a promising solution for generating secret keys. While complementary metal–oxide–semiconductor‐based PUFs have been extensively studied, their reliability and scalability limitations have spurred the search for alternative approaches. This study introduces a spintronic PUF device that utilizes an indirect magnetic coupling, specifically the Ruderman–Kittel–Kasuya–Yosida (RKKY) interaction. This unique interaction enables either parallel or antiparallel coupling of ferromagnetic layers controlled by the thickness of a nonmagnetic spacer such as ruthenium (Ru). This study presents heterostructures of β‐W/CoFeB/MgO/Ti/CoFeB/Ru/CoFeB/Ta, with Ru thicknesses ranging from 1.4 to 2.4 nm. Nonuniform argon‐ion milling to the Ru layer generates stochastic distributions of RKKY interaction, resulting in unpredictable field‐free switching behaviors. The PUF devices exhibit exceptional characteristics, including ideal reliability, near‐unity entropy (averaging 0.994), and remarkable endurance of up to 20 000 current pulses for a single‐unit device. Furthermore, these devices maintain functionality across a wide temperature range from −55 to 150 °C, making them suitable for automotive applications.