High-Throughput Fabrication of Anti-Counterfeiting Nanopillar-Based Quick Response (QR) Codes Using Nanoimprint Lithography

Abstract

Quick response (QR) codes are two-dimensional optical labels which store information instantly readable by an imaging device (smartphone camera). They can be used as anti-counterfeiting elements to help companies and consumers identify the authenticity/traceability of the products. Three-dimensional nanostructured QR codes are a new class of increased level of security labels to better support product authentication. In this work, nanoimprint lithography (NIL) was used to fabricate flexible, high resolution three-dimensional (3D) QR codes with selective and reflective properties, suitable as anti-counterfeiting elements. The original design and the optical properties of the fabricated label are given by a bicolor pattern, where one color is diffractively generated by a set of 300 nm pitch nanopillars and the second color arise from a set of 400 nm pitch nanopillars, together comprised in the shape of a nanostructured based QR code. The glass transition temperature (Tg ) of the flexible and transparent imprinted substrate (Intermediate Polymer Substrates – IPS) was assessed by differential scanning analysis (DSC). Scanning electron microscopy (SEM) images were used to optimize the NIL imprinting parameters. Optimal individual nanopillars with straight sidewalls were visualized when the imprinting temperature was slowly decreased and a constant imprinting pressure was maintained constant throughout the imprinting process. A good replication of the mold in the thermoplastic substrate is of key importance to an accurate reading of the label.