Optical signal and image processing device optimized for optical readout

Large area (4 × 4 cm2) optical signal and image processing (OSIP) devices were produced at low temperatures by Plasma Enhanced Chemical Vapour Deposition (PE-CVD). The OSIP device consists of two stacked sensing/switching diodes (p(SiC:H)/i(Si:H)/n(SiC:H)) with an internal light blocking layer between them and two semitransparent contacts. An optical scanner is used for charge readout. In this work the main emphasis will be put on the analysis of the optical characteristics. The use of a metal grid (290 × 290 μm2 Cr pixels with 40 μm spacing) between the two diodes, working as light screening layer or as floating anode via an a-SiN insulator layer, is analyzed. Its influence on the transfer functions, resolution, responsivity and response time of the sensor is presented. The optical-to-electrical transfer characteristics show high quantum efficiency, broad spectral response, and reciprocity between the optical and the electrical images. When the light screening floating anode is present an effective optical decoupling from both photodiodes is achieved while maintaining a good electrical conductivity and an increased light-to-dark sensitivity. A trade-off is established between sensor design and light pattern and scanner wavelengths in order to minimize the cross talk between the write and the read beams and to improve the light to dark sensitivity.