A CMOS Photodetector for Direct Color Imaging

A novel photodetector for imaging in the visible-near infrared range is investigated. Unlike currently used detectors, the proposed device does not require thin film filters for spectral discrimination. Instead, the discrimination relies on the wavelength-dependent absorption property of semiconductor materials. The detector consists of a window exposing the silicon substrate to the electromagnetic signal. Besides the window, multiple collectors separated by polysilicon gates are laid out. Proper voltage biasing establishes a different spectral response for each collector, thus creating a detection color space. Experimental results demonstrate the color detection capability of a three-collector imaging pixel from sensitivity metamerism index calculations. The sensor is fabricated in a standard 0.35-μm CMOS process and presents a peak combined collectors' responsivity of 0.35 A/W.