Physically\nUnclonable Cryptographic Primitives by\nChemical Vapor Deposition of Layered MoS₂

Abstract

Physically\nunclonable cryptographic primitives are promising for\nsecuring the rapidly growing number of electronic devices. Here, we\nintroduce physically unclonable primitives from layered molybdenum\ndisulfide (MoS₂) by leveraging the natural randomness of\ntheir island growth during chemical vapor deposition (CVD). We synthesize\na MoS₂ monolayer film covered with speckles of multilayer\nislands, where the growth process is engineered for an optimal speckle\ndensity. Using the Clark–Evans test, we confirm that the distribution\nof islands on the film exhibits complete spatial randomness, hence\nindicating the growth of multilayer speckles is a spatial Poisson\nprocess. Such a property is highly desirable for constructing unpredictable\ncryptographic primitives. The security primitive is an array of 2048\npixels fabricated from this film. The complex structure of the pixels\nmakes the physical duplication of the array impossible (<i>i.e.</i>, physically unclonable). A unique optical response is generated\nby applying an optical stimulus to the structure. The basis for this\nunique response is the dependence of the photoemission on the number\nof MoS₂ layers, which by design is random throughout the\nfilm. Using a threshold value for the photoemission, we convert the\noptical response into binary cryptographic keys. We show that the\nproper selection of this threshold is crucial for maximizing combination\nrandomness and that the optimal value of the threshold is linked directly\nto the growth process. This study reveals an opportunity for generating\nrobust and versatile security primitives from layered transition metal\ndichalcogenides.