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

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)3O4 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.