Biometric system based on one single large area a-SiC:H p-i-n photodiode
- PDF / 1,060,034 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 42 Downloads / 137 Views
Biometric system based on one single large area a-SiC:H p-i-n photodiode M. Vieira, M. Fernandes, A. Fantoni, P. Louro, R. Schwarz Electronics Telecommunications and Computer Dept., ISEL, R. Conselheiro Emidio Navarro, P 1949-014 Lisboa, Portugal. Tel: +351 21 8317181, Fax: +351 21 8317114, E-mail: [email protected]. ABSTRACT 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 µm. A further increase in the contrast is achieved by slightly reverse biasing the sensor with a sensitivity of 6.5 µWcm-2 and a flux range of two orders of magnitude. INTRODUCTION Studies on the use of glass/ITO/p /i /n /metal structures as Laser Scanned Photodiode (LSP) image sensors have recently shown its potential capability [1, 2] as monochrome image sensing devices. These devices are fundamentally different from the other electrically scanned image sensors [3, 4]. They consist on one single large cell detector or pixel (picture element) and the image is scanned by sequentially detecting scene information at discrete XY coordinates. The read-out of the injected carriers is achieved by measuring the ac component of the current, iac, in short circuit mode. They detect an optical image (monochrome image) with a spatial resolution of 30 µm in a flux range of two orders of magnitude and present a sensitivity of 6.5 µWcm-2. Advantages to this approach are high resolution, uniformity of measurement from one side to the other and the cost/simplicity of the detector. The design allows a continuous sensor without the need for pixel-level patterning, and so can take advantage of amorphous silicon technology. Also it can be integrated into a system where the signal processing can be performed by an ASIC chip underneath. This work aims to clarify possible improvements, physical limits and performance of the LSP image sensor when used in a biometric system for fingerprint authentication. Here, the biometric capture device and the scanning reader are optimized and the effects of the sensor structure on the output characteristics discussed.
K10.6.1 Downloaded from https://www.cambridge.org/core. Teachers College Library - Columbia
Data Loading...
