Vertically Integrated Image Sensor Photodetectors

The patent inverts the conventional front-side illumination architecture to back-side illumination, where light enters through the back surface of the substrate. This reversal positions electrical conductors on the front surface away from the light path, eliminating light blocking while maintaining electrical connectivity. The photodetectors are configured to collect charge carriers generated by light absorbed in the substrate, with conductors extracting signals from the opposite surface.

The patent transitions from two-dimensional planar photodetector designs to three-dimensional vertically integrated structures. Multiple photodetector layers are stacked along the vertical axis, allowing each pixel to contain several photodetectors at different depths. This vertical stacking increases charge capacity and spectral discrimination capability without increasing the lateral pixel footprint, thereby maintaining high device density while enhancing charge storage capacity.

The patent segments the monolithic substrate into multiple bonded wafer layers, each containing specific photodetector types and optical elements. By fabricating separate wafer stacks independently with precise patterning, then bonding them together, the method avoids grid distortions that would otherwise occur in a single thick substrate. Each layer can be optimized and fabricated separately, ensuring accurate color filter alignment and reducing crosstalk.

The patent merges multiple photodetector functions into a single vertically integrated pixel structure. Multiple photodetectors share common readout circuitry and control lines, eliminating the need for separate transistors and storage nodes for each detector. The vertical stacking allows photodetectors to share horizontal circuit resources, achieving global electronic shutter operation with correlated double sampling while maintaining small pixel area through resource sharing and functional integration.