Laser Generation of Sub‐Micrometer Wrinkles in a Chalcogenide Glass Film as Physical Unclonable Functions

Abstract

Laser interaction with solids is routinely used for functionalizing materials' surfaces. In most cases, the generation of patterns/structures is the key feature to endow materials with specific properties like hardening, superhydrophobicity, plasmonic color‐enhancement, or dedicated functions like anti‐counterfeiting tags. A way to generate random patterns, by means of generation of wrinkles on surfaces resulting from laser melting of amorphous Ge‐based chalcogenide thin films, is presented. These patterns, similar to fingerprints, are modulations of the surface height by a few tens of nanometers with a sub‐micrometer periodicity. It is shown that the patterns' spatial frequency depends on the melted layer thickness, which can be tuned by varying the impinging laser fluence. The randomness of these patterns makes them an excellent candidate for the generation of physical unclonable function tags (PUF‐tags) for anti‐counterfeiting applications. Two specific ways are tested to identify the obtained PUF‐tag: cross‐correlation procedure or using a neural network. In both cases, it is demonstrated that the PUF‐tag can be compared to a reference image (PUF‐key) and identified with a high recognition ratio on most real application conditions. This paves the way to straightforward non‐deterministic PUF‐tag generation dedicated to small sensitive parts such as, for example, electronic devices/components, jewelry, or watchmak.

Sub‐Picosecond Non‐Equilibrium States in the Amorphous Phase of GeTe Phase‐Change Material Thin Films

“…However, the formation of fingerprints patterns observed by post‐experiment phase‐contrast microscopy (see ref. [40] and Figure , Supporting Information) leaves no doubt on the formation of a liquid layer for F ≥ 26 mJ cm −2 . The volume of melted material increases with time as the front of the liquid phase propagates thanks to thermal transport, and the shrinkage becomes large enough to be detected.…”

“…FDI results presented in Figure 1 clearly indicate a transition from the as‐deposited GeTe to another state upon laser excitation. Since post‐experiment nano‐beam electron diffraction analysis within the irradiated volume of the GeTe film reveals no sign of crystallization, [ 40 ] the final state is also an amorphous state, but distinct from the initial one as evidenced by the change of refractive index shown on the optical microscope pictures (Figure , Supporting Information). To identify the origin of the underlying process behind this transition, we conducted ab initio molecular dynamics (AIMD) simulations.…”

Laser fabrication and evaluation of holographic intrinsic physical unclonable functions

“…Any random physical process is a potential candidate for the realization of PUFs. Indeed, there is already a plethora of research accounts 12 – 19 that include exotic solutions like aerogels 20 , Raman tags 21 , plasmonic nanopapers 22 wrinkles on glasses 23 , perovskite fluorescent dots 24 or even edible unclonable functions 25 to name a few. The PUF scenery in the literature is evolving fast necessitating taxonomy activities like the one presented by McGrath and co authors 12 .…”

“…In most PUF demonstrations, although security of goods and services is evoked, it is surprising that these are rarely assessed in terms of practical implementation both in terms of industrial compatibility for upscaled production and PUF evaluation apparatus for Challenge Response Pair (CRP) behavior at the end user. In this context, it is hard to envisage how the various demonstrations like 20 , 23 , 24 mentioned above will be incorporated in an industrial fabrication of everyday goods or how bulky machinery, such as the spectroscopic equipment required in Ref. 21 , can be used for read out of PUF response somewhere in the supply chain.…”

Flexible and Biocompatible Physical Unclonable Function Anti‐Counterfeiting Label

“…[ 24 ] While, this flexible PUF is a contact and non‐optical PUF without biocompatibility. Optical PUFs, as a typical example of non‐silicon PUFs, have been studied extensively, [ 25,26 ] which have been applied for different scenarios due to the non‐contact and fast optical reading properties. [ 11,12,27 ] However, most of the optical PUFs are rigid without good biocompatibility and flexibility, which cannot be applied for products with complex surface, and thus limiting their application.…”