Hierarchical Physically Unclonable Functions From CVD‐Grown Two‐Dimensional High‐Entropy Spinel Oxide Nanoflakes

ABSTRACT Physically unclonable functions (PUFs) provide hardware‐rooted security by converting intrinsic material randomness into unique cryptographic fingerprints. However, most existing PUF systems rely on a single entropy source, limiting key capacity and adaptability for hierarchical authentication. Here, we report a hierarchical PUF architecture based on two‐dimensional high‐entropy spinel oxide (CoCrFeMnNi) 3 O 4 nanoflakes synthesized by molecular sieve‐assisted chemical vapor deposition. The triangular nanoflakes exhibit two energetically degenerate in‐plane orientations that can be used for rapid, low‐cost key extraction. This kind of PUF demonstrates excellent cryptographic characteristics with near‐ideal bit uniformity, high inter‐device uniqueness, and strong resistance to environmental perturbations including illumination variation, thermal treatment, and chemical exposure. Meanwhile, the stochastic occupation of lattice sites by multiple metal cations within the high‐entropy structure produces atomic‐scale compositional fluctuations, which provides a second, high‐density entropy source. The elemental intensity fluctuations are further processed through permutation and multi‐element encoding to generate cryptographic keys with extremely large capacity. By integrating independent entropy channels at different structural scales within a single material system, this work establishes a materials‐centric strategy for hierarchical and intrinsically unclonable hardware security, offering a scalable platform for next‐generation Internet‐of‐Things and edge‐computing authentication technologies.