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Micro and nanosystems
The fingerprint sensor developed under the EU PiezoMAT project has set a new record. The eight-partner project consortium, which included CEA Tech institute Leti, developed a device that achieved resolutions of more than 1,000 dpi—better than what is required by the FBI and two times the minimum requirement in the project specifications.
The sensor is made up of bundles of ZnO nanowires, each of which forms a pixel connected at the top and bottom of each bundle. The ZnO nanowires have piezoelectric properties; they can produce an electric current and return to their original shape after compression or flexion. In other words, when a finger is placed on the sensor, local deformation of the nanowire network generates an electric potential whose amplitude is proportionate to the nanowires' displacement. This is how the sensor distinguishes the pores and ridge edges of a fingerprint.
Leti's researchers had to overcome several challenges to achieve this advance. First, they obtained an array of Ga-doped ZnO contacts on a silicon chip with a high pattern density. The chip was designed and fabricated on a 200 mm wafer in a cleanroom. A 250-pixel prototype was tested by IDEMIA.
CEA is a French government-funded technological research organisation in four main areas: low-carbon energies, defense and security, information technologies and health technologies. A prominent player in the European Research Area, it is involved in setting up collaborative projects with many partners around the world.