A robust, 1.8 V 250 μW direct-contact 500 dpi fingerprint sensor

Abstract

This high-resolution, low-power direct-contact capacitive sensor using standard CMOS front-end processing exhibits high sensitivity while maintaining an effective barrier to chemical, physical and electrostatic intrusion. The sensor uses direct finger contact with the surface of the sensor IC to capture a capacitive fingerprint image. The sensor consists of a 2-D array of metal plates capped with a thin dielectric layer. Unlike previous designs, each sensing site uses one metal sensor plate. Each functions as capacitor bottom plate, with the finger surface acting as the grounded top plate. Distance between the finger and the sensor and hence the measured capacitance varies with the pattern of ridges and valleys in the fingerprint. The capacitance is "measured" as the change in voltage that results when a fixed charge is removed from each sensing plate.