Monolithic Plasmonic Tokens Enabled by Physical Deposition

Abstract

Optical physically unclonable functions (PUFs) exploit intrinsic nanoscale physical randomness to generate unique and irreproducible optical fingerprints. However, most existing fabrication methods rely on multi-step processes or wet chemical synthesis or coating in solution, limiting environmental stability and their integration into microelectronics. To address this, this thesis describes a monolithically fabricated plasmonic PUF keys, based on a physical vapor deposition, compatible with standard microfabrication workflows. Particularly, glancing angle deposition (GLAD) is employed to induce stochastic formation of plasmonic nanoislands by depositing a metal layer onto a metallic mirror separated by a dielectric spacer. By employing only two primary materials, the resulting plasmonic metasurfaces exhibit optical scattering patterns that serve as intrinsically unclonable hardware tokens. The performance of the fabricated PUF is characterized by a bit uniformity of 0.505, an inter-Hamming distance of 0.492 ± 0.008, and an astronomical physical decryption time of 1 x 1018814 seconds, demonstrating exceptional uniqueness, reliability, and cryptographic robustness. Furthermore, the dielectric capping layer provides a dual advantage of protection of nanostructures and precise reflective color tuning through photonic interference. This fabrication strategy is highly scalable and cost-effective as it uses inexpensive metal. More crucially, this thesis demonstrates a rapid authentication process in which the plasmonic tokens are stored in and verified against a database, highlighting their potential for deployment in industrial scale security and authentication systems.