Optical characterization of integrated P+/N-Well/P-substrate and N-Well/P-substrate photo-device structures on CMOS technology

Here, a characterization methodology for integrated silicon-based photo-devices is presented. Devices are phototransistors (“P+/N-Well/P-substrate”) and photodiodes (“N-Well/P-substrate”) with similar sizes, (9μm×9μm). They were integrated in a 1.5μm CMOS technology through MOSIS. Through these characterizations it is possible also to find out in general, the performance advantages and disadvantages, comparing measurements made on these kinds of structures. It was found that phototransistors have a better performance compared with photodiodes. The contribution from substrate leakage current in N-Well/P-substrate structures is high, as well as from carriers generated in the neighborhood of the pixel circuit. It is shown that crosstalk is the phenomenon that deviates the measured photo-response from the ideal model of photo-devices.