The contact geometry in a 2D μc-Si:H p-i-n imager

A two-dimensional imager has been designed and produced based on μc-Si:H material. The basic building block for the sensor element is a TCO/μc-p-i-n Si:H photodiode with two front metal contacts and a back TCO transparent one. A scan-out process obtains the image. The effect of the contact geometry on the sensor output characteristics (linearity, distortion, sensitivity and signal-to-noise ratio) were studied by systematic variation of the metal contact pattern (rectangular, L-like). The highest sensitivity has been achieved with L-like contacts. The differential responsivity shows a 10% linearity increase and a 30% image distortion decrease when the contact shape changes from rectangular to L-like. By using L-like front contacts a full 2D imaging has been achieved with a dynamic range of about 32 dB and a signal-to-noise ratio of about 37 dB without significant image distortion. A basic model that takes into account the physics of the sensor element and the transducer behaviour is presented. Simulation results are analysed and compared with the experimental data. Basic image processing algorithms will be developed for image enhancement (contrast, edge, noise filtering, sharpening) and restoration (deblurring, geometric distortion, non-linearity).