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PIEZOMAT

ULTRA-HIGH-RESOLUTION SENSING USES VERTICAL PIEZOELECTRIC NANO-WIRE MATRICES TO RECONSTRUCT THE SMALLEST FEATURES OF HUMAN FINGERPRINTS

FP7-ICT-2013-10 > | Grant agreement ID: 611019

November 2013 – June 2017

The PiezoMAT project focused on the development of new technology high-resolution fingerprint sensors based on a matrix of interconnected piezoelectric nanowires (NWs). The long-term objective of PiezoMAT was to offer high-performance fingerprint sensors with minimal volume occupation for integration into built-in systems able to compete in the market with the best existing products.

PIEZOMAT

ULTRA-HIGH RESOLUTION SENSING USES VERTICAL PIEZOELECTRIC NANO-WIRE MATRICES TO RECONSTRUCT THE SMALLEST FEATURES OF HUMAN FINGERPRINTS

FP7-ICT-2013-10 > | Grant agreement ID: 611019

November 2013 – June 2017

The PiezoMAT project focused on the development of new technology high-resolution fingerprint sensors based on a matrix of interconnected piezoelectric nanowires (NWs). The long-term objective of PiezoMAT was to offer high-performance fingerprint sensors with minimal volume occupation for integration into built-in systems able to compete in the market with the best existing products.

diagram piezomat project

Fingerprint sensors : from modelling to material design

PiezoMAT proceeds by local deformation of an array of individually contacted piezoelectric NWs and reconstruction from generated potentials, whose amplitudes are proportional to the NW displacement. Each NW and its associated electronics constitute a sensor, or pixel. Typical resolution of current fingerprint sensors constitutes 500 dpi, which conforms to the FBI standard for the detection of level 1 (pattern) and level 2 (minutiae) features. However, at least 1000 dpi is required to extract the tiniest level 3 features such as shape of pores and ridge edges.

In this project, SPECIFIC POLYMERS worked on the elaboration of a specific encapsulation polymeric layer for a new design of a pressure sensor that is expected to provide higher resolution and minimal volume occupation compared to existing setups. Fragile NWs cannot undergo direct contact with the finger; therefore, a polymeric encapsulation layer is required to simultaneously provide physical protection and to transfer the force from the finger to the NWs. To ensure sensor robustness, the polymeric layer must also exhibit appropriate chemical inertness, and water- and oil-repellency.

To achieve this aim, novel formulations of UV-crosslinkable polymeric materials were developed, prepared and deposited as thin layers on the NWs using spin-coating, following the recommendations derived from numerical simulations. We succeeded in determining the ideal balance between polymer formulation processability and the final thin layer’s characteristics (Young’s modulus and thickness). The resulting encapsulation layer was proved to properly protect the piezoelectric ZnO nanowires from breaking under pressure forces and from being contaminated with external impurities while enabling successful collection of electrical signals in a bottom–bottom contacted NW configuration.

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