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CEA-Leti and Partners in PiezoMAT Project developed New Fingerprint Technology for Highly Reliable Security and ID Applications

Ultra-high Resolution Pressure Sensing Uses Matrices of Vertical Piezoelectric Nanowire

to Reconstruct the Smallest Features of Human Fingerprints

 a research project funded by the European Commission in the Seventh Framework Program (FP7, grant No. 611019)

The PiezoMAT team

The European project PIEZOMAT proposes a new technology of very high-resolution fingerprint sensors based on a matrix of interconnected piezoelectric ZnO nanowires (NWs). 

The direct consequence of integrating nano-objects on microelectronic chips rather than conventional microsystems is to diminish the size of individual pixels, which enables larger integration densities and thus higher spatial resolutions (>1000 dpi).

PiezoMATexplores 3 possible configurations with the charge collections at the bottom of single nanowires or with top-bottom contacts.

Partners challenges were the integration of ZnOnanowires, onto microelectronics chips (200mm wafer), considering process compatibility at the wafer scale of the successive nanowire growth, contacting and encapsulation steps.

    Principle

    • Each nanowire or bundle of nanowires forms a pixel (size below 50 × 50 µm2)
    • Pixel encapsulated in a polymer
    • Generated potentials are proportional to the NW displacement

    Chip processing

    Challenges: High patterning density, choice of proper materials (especially seed layer), chouce of appropriete process (only dry processes due to seed layer sensitivity), integration

    Following steps on dies

    • Nanowire growth
    • Encapsulation
    • Top electrode
    • Bonding
    • Testing

    option - BENDING

    • 2 contacts in high potential area
    • 5000dpi – 8 × 8 pixels
    • Technologically challenging
       

    • First experimental demonstration of bottom-bottom contacted 'bending mode’ force sensor 
    • Very high gauge factor and force sensitivity on the active NWs 

    option - COMPRESSING

    • 2 top-bottom contacts
    • 1000dpi – 25 × 10 pixels
    • Technologically safer

    Results - Conclusions

    3 demonstrators by 3 partners: one live demonstration and 2 videos

    • Morpho: peak response to mechanical contact (250 pixels)
    • MFA: pattern recognition and position sensitivity (128 pixels, one by one)
    • Fraunhofer: the 8-bit detection is successfully demonstrated (80 pixels)
       

    Morpho characterisation: peak respons of 250 pixels

    MFA characterisation: position sensitive pattern recognition by 128 pixels