Physically Unclonable Function Utilizing Stochastic Indirect Exchange Interaction

초록

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 beta-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 degrees C, making them suitable for automotive applications.

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