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.


    • 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
    • Development of stable and reproducible process in clean-room
    • Successful NWs integration: localized and contacted NWs growth on a processed 200 mm silicon wafer
    • Development of a suitable UV-crosslinkable polymeric formulation and an accurate deposition process for the encapsulation
    • Development of highly conductive top electrodes
    • Demonstration of the feasibility of the compression option → full device setup for MORPHO’s application

    Results - Conclusions

    3 demonstrators by 3 partnersone 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

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