Biometric piezo scanner

Abstract

A piezoelectric thin film sensor array is used to scan and capture biometric data, for example, a fingerprint image. In one embodiment, a multi-layer structure includes a PVDF layer in between two conductor grids arranged orthogonally to one another. Urethane can be added to one side where a finger is placed. A foam substrate can be used as a support. In one feature, the PVDF, and grids can be peeled off like a label for easy replacement. Multiplexers are switched to scan the sensor. A single pixel or a group of pixels can be detected and output to an image memory. The presence of a fingerprint ridge is detected by virtue of a ring-down oscillation that arises from reflection when an electric field is applied to the piezoelectric thin film sensor array at a pixel in contact with the fingerprint ridge. For example, such a ring-down value associated with a fingerprint ridge can be detected at about 150 ns. (or 5 cycles at 30 MHZ). Other reflections indicative of additional biometrics (e.g. from tissue, blood, bone, fingernail, etc.) can also be detected. A Doppler effect due to reflections from circulating blood can also be detected. Such a Doppler effect can provide further information about direction and speed of blood circulation. An instantaneous pyroelectric effect can also be detected to indicate a live finger presence.

1 . A biometric sensing device, comprising: a first conductor grid including a first set of conductors; a second conductor grid including a second set of conductors arranged orthogonally to said first set of conductors such that pixels within an array of pixels correspond to regions where ones of said first set of conductors cross ones of said second set of conductors; and a piezoelectric film disposed between said first and second conductor grids; wherein biometric data can be produced by applying an electric pulse to a pixel through said first and second conductor grids and measuring a voltage across said first and second conductor grids at said pixel subsequent to said application of said electric pulse. 
     
     
         2 - 17 . (canceled)