Tiny structures for security – Nano Argovia project LASTRUPOL researchers are developing a new fabrication process for security features

 

In the Nano Argovia project LASTRUPOL, researchers from the FHNW School of Engineering, the Paul Scherrer Institute (PSI) and the company Gemalto AG (Aarau) are working together to develop a new fabrication process for security features on identity documents. The aim of the project is to produce three-dimensional optical structures with high precision and surface quality using the most economical process possible.

Lasered test structures in polymers need to be smoothed. (Image: M. Kristiansen, School of Engineering, FHNW)

First structured, then smoothed
The team working under project leader Professor Dr. Per Magnus Kristiansen begins by using ultrashort laser pulses to remove material from a plastic surface in a targeted manner. Once engraved with these microscale structures, the surface is then smoothed to a roughness of less than 100 nanometers in a process that leaves the fine structures unaffected.

To do this, the scientists use a contactless method that was investigated in the Nano Argovia project SurfFlow and that reduces the glass transition temperature (the temperature at which the polymers change from a solid state into a thick molten mass) on the surface. If the sample is heated gently following this preliminary treatment, only the treated uppermost layers reach their glass transition temperature and become smooth, while the underlying structure and deeper layers remain virtually unchanged. In the LASTRUPOL project, this method must now be adapted to new materials and larger structures – an apparently simple proposition that actually presents a considerable challenge.

The combination of the two techniques should then lead to the production of templates that allow various security features to be reproduced easily. To begin with, the researchers are applying this method to two different types of security features: Firstly, to optical features produced by differences in diffraction on the structures; and secondly, to those created by tiny lenticular and spherical plastic lenses.

New technologies are key 
“We’re a leading company in the area of digital and physical identity solutions,” explains Dr. Christian Sailer, Head of Physical Document Security R&D Switzerland at the project’s industry partner, Gemalto AG. “It’s vital for us to invest in new technologies aimed at producing security products in order to maintain this leading position. The Nano Argovia project LASTRUPOL is an excellent opportunity to benefit from the expertise of plastics processing specialists at the School of Engineering and the PSI.”

“The Nano Argovia project LASTRUPOL is an excellent opportunity to benefit from the expertise of plastics processing specialists at the School of Engineering and the PSI.»

Dr. Christian Sailer, Gemalto AG (Aarau, AG)