RF Sensor-Based Liveness Detection Scheme With Loop Stability Compensation Circuit for a Capacitive Fingerprint System

A capacitive fingerprint system is the most widely used biometric identification method for smartphones. In this paper, we propose a RF sensor-based liveness detection scheme. This method solves the problem of spoofing attacks, which is a primary disadvantage to capacitive fingerprint sensors. The proposed scheme measures the inherent impedance characteristic difference of the target fingerprint caused by the eddy-current effect with an auto-balancing bridge method. The magnetic field is generated by a small form-factor inductor coil of $\phi =1.5$ mm. This detection scheme can be easily integrated with an existing capacitive fingerprint sensor by using the same CMOS process. The measured results demonstrate the liveness detection capability of the Si-graphite (silicone-graphite) and polyvinyl fake fingerprints that cannot be distinguished by conventional capacitive fingerprint sensors.