Based on the Laser Scanned Photodiode (LSP) image sensor we present an optical fingerprint reader for biometric authentication. The device configuration and the scanning system are optimized for this specific purpose.
The scanning technique for fingerprint acquisition is improved and the effects of the probe beam size, wavelength and flux, the scan time and modulation frequency on image contrast and resolution will be analyzed under different electrical bias. An optical model of the image acquisition process is presented and supported by a two dimensional simulation.
Results show that a trade-off between read-out parameters (fingerprint scanner) and the biometric sensing element structure (p-i-n structure) are needed to minimize the cross talk between the fingerprint ridges and the fingerprint valleys. In the heterostructures with wide band gap/low conductivity doped layers the user-specific information is detected with a good contrast while the resolution of the sensor is around 20 νm. A further increase in the contrast is achieved by slightly reverse biasing the sensor with a sensitivity of 6.5 νWcm-2 and a flux range of two orders of magnitude.