Characteristics of Fingerprint Sensing on Capacitive Fingerprint Sensor LSIs with a Grounded Wall Structure

概要

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This paper describes the dependence of fingerprint-sensing characteristics on sensed and parasitic capacitances. The sensed capacitance is formed between the sensor plate covered with a sensing insulator and the finger surface, which contacts the fingerprint sensor LSI. The parasitic capacitance is mainly formed on the grounded (GND) wall and metal layer under the sensor plate through the dielectric film. To investigate the dependence, we propose a circuit model of the GND wall structure that takes these capacitances into consideration. We analyzed the output dynamic range of the sensing circuit by varying the sensed and parasitic capacitances, which were changed by the sensor plate size and thickness of the sensing insulator and the dielectric film. The analysis and experimental results revealed that there are an optimal sensor plate size and suitable thickness of the sensing insulator and the dielectric film to effectively detect the sensed capacitance. These findings enable us to design the most effective GND wall structure to capture clear fingerprint images.
INSTITUTE OF PURE AND APPLIED PHYSICSの論文
2002-10-15