Laser-Induced Stochastic Copper Microstructures for Flexible Physically Unclonable Labels.

Physically unclonable functions (PUFs) are a promising solution for anticounterfeiting technologies. However, their mass implementation is limited by fabrication complexity and/or special materials demands, as well as specialized authentication. To overcome these issues, a scalable and sustainable approach for fabricating optical PUF labels is proposed in this work. The approach is based on direct laser metallization (DLM) of deep eutectic solvents on flexible polyimide substrates. The laser-induced reduction of copper precursors produces microstructures made by specially designed templates with stochastic edge morphologies serving as unique unclonable identifiers. A computer vision-based authentication algorithm enables robust recognition, achieving an encoding capacity exceeding 10465. The created labels can be authenticated using standard microscopes or consumer smartphones with macro lenses. Additionally, created labels were tested for stability and unauthorized copying. The replication attempts using 1200 dpi laser printing reproduced macroscopic outlines but failed to mimic microscopic features, confirming their unclonability. The fabricated labels remain functional after exposure to running water and heating up to 200°C, demonstrating excellent environmental durability. Due to its flexibility, scalability, and low-cost eco-friendly processing, the proposed label design is well suited for integration into flexible and wearable microelectronic systems, providing a practical solution to next-generation anticounterfeit technologies.