Stacked pixels for high resolution cmos image sensors with bcmd charge detectors

Abstract

The invention describes in detail a solid-state CMOS image sensor, specifically a CMOS image sensor pixel that has stacked photo-sites, high sensitivity, and low dark current. The pixels have incorporated therein special potential barriers under the standard pinned photodiode region that diverts the photo-generated electrons from a deep region within the silicon bulk to separate storage structures located at the surface of the silicon substrate next to the pinned photodiode. The storage structures are p channel BCMD transistors that are biased to a low dark current generation mode during a charge integration period. The signal readout from the BCMD is nondestructive, therefore, without kTC noise generation. Thus a single pixel is capable of detecting several color-coded signals while using fewer or without using any light absorbing color filters on top of the pixel. The image sensors constructed with the stacked photo-sites with BCMD readout have higher pixel densities, higher resolution, higher sensitivity, very low dark current, and no color aliasing if at least three depth encoded signals are read from a single photodiode. The pixels having stacked photo-sites with BCMD readout are particularly suitable for a CMOS image sensor that is illuminated from the back side.