Integrated color detectors in 0.18mum CMOS technology
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A method for improving photodetectors' spectral sensitivity using a commercial 0.18μm silicon CMOS technology was demonstrated. The new devices combine buried double junction or buried triple junction photodetectors with metallic grids as gratings above the detectors. One dimensional and two dimensional metal gratings with minimum width and different periodicities were formed with the standard metal-1 layer in the TSMC process. The photodetectors were illuminated by monochromatic light within the visible region. The p-n junctions of the detectors were reverse-biased to collect the photogenerated charge. Photocurrents from different junctions of the detectors were measured at wavelengths from 400nm to 700nm with a step of 10nm. The spectral sensitivities were evaluated using the ratio of the output photocurrents generated from different layers, and were compared for the detectors without metal gratings and with gratings of different periodicities. Enhanced spectral sensitivity was demonstrated by the combination of the buried double (triple) junction detectors and metallic grids, the first time this has been reported using only a commercial CMOS process without customized masks or fabrication parameters. This method eliminates the necessity of incorporating external optical filters to differentiate colors, thus reduces manufacturing cost significantly.