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.