Material Limitations Which Cause Striations in CCD Imagers

It has been established experimentally that the striation contrast observed in the background of the video signal from frame-transfer CCD imagers is related to the resistivity inhomogeneities and/or fluctuations in recombination center concentration which had been formed in the silicon wafers during crystal growth. A qualitative model was developed which explains the effect of these material parameters on the collection of photocurrent by the charge-storage wells (MOS capacitors) for different operating conditions. From the analysis of experimental data it was established that the main contribution to the formation of striation contrast is from the effects which material inhomogeneities exert on the collection of carriers generated under those gates which form potential barriers surrounding the charge collection wells. The individual contribution to the formation of striation contrast due to resistivity variations and recombination center fluctuations has been determined.