Silicon sensor transforms RF fields into fingerprint images

If electronic fingerprint recognition is to become widely used for human identification, it must work reliably under worldwide conditions. The variety of finger and skin conditions existing among the world`s populations, combined with the large number of different worldwide environments in which fingerprint sensors must operate, make electronic fingerprinting a complex imaging task.

Jul 1st, 1999

Silicon sensor transforms RF fields into fingerprint images

If electronic fingerprint recognition is to become widely used for human identification, it must work reliably under worldwide conditions. The variety of finger and skin conditions existing among the world`s populations, combined with the large number of different worldwide environments in which fingerprint sensors must operate, make electronic fingerprinting a complex imaging task.

In the past few decades, several surface-based technologies for reading fingerprint patterns have emerged. These include the FC15A140 FingerChip from Thomson-CSF (Totowa, NJ), a thermal CMOS sensor that uses the finger`s heat to capture several successive images and then reconstructs them into a full fingerprint via a proprietary algorithm (see Vision Systems Design, May 1999, p. 10).

Now, AuthenTec (Melbourne, FL) has developed a fingerprint sensor, called FingerLoc, which uses small electric fields to detect an image of the finger ridges and valley patterns (see figure). During operation, the device measures subsurface features by generating and detecting linear field geometries that originate from the inherent conductive layer of skin cells that lie beneath the skin surface.

During sensor operation, a small RF field is applied between a conductive layer in the silicon device and the conductive layer under the fingers` skin. The fields formed between these conductive surfaces replicate the shape of the conductive skin layer via the amplitude of a generated ac field. They are detected by tiny sensor plates located beneath the surface of the semiconductor and above the continuous skin conductive layer. Amplifiers buried beneath each pixel sensor plate convert the potentials on the plates to signal voltages that represent the fingerprint pattern. These signals are then multiplexed from the sensor array.

This technology does not depend on skin-surface features such as the air gap between the sensor and the fingerprint valleys. As a result, fingerprints that are difficult to image using optical or dc capacitive sensors can be imaged using the FingerLoc device.

Designed to minimize costs when connected to a PC, the FingerLoc sensor can be interfaced via the standard universal asynchronous receiver-transmitter (UART) found on most PC super input/output chips. And, because the fingerprint sensor is active only during a percentage of the system operating time, it can share a UART with another serial device such as a modem or an external serial port.

AuthenTec has formed a strategic relationship with Paradise Innovations (Fremont, CA), a designer of PC multimedia and communications products, to develop and market fingerprint-sensor-security applications for the computer-peripheral market. Both companies have demonstrated a computer-based fingerprint-identification log-on system that eliminates the Microsoft Windows 98 log-on password.

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