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
- Nanowire growth
- Top electrode
- 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
- 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
- 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