Image sensors with multi-photodiode image pixels and vertical transfer gates

A method of operating an image sensor having an array of image pixels, wherein each image pixel in the array of image pixels has an inner photosensitive region, an outer photosensitive region that surrounds the inner photosensitive region, and readout circuitry, the method comprising:

• accumulating charges at the inner and outer photosensitive regions of a given image pixel of the array of image pixels;
• while accumulating the charges at the outer photosensitive region, using a global vertical transfer gate structure that is coupled to the outer photosensitive region to drain excess accumulated charges from the outer photosensitive region;
• using a local vertical transfer gate, transferring the accumulated charges from the inner photosensitive region to a first charge storage region while simultaneously transferring the accumulated charges from the outer photosensitive region to a second charge storage region;
• reading out the charges transferred to the first charge storage region using the readout circuitry in the given image pixel;
• and
• reading out the charges transferred to the second charge storage region.

An image sensor, comprising:

• a global vertical transfer gate structure with a grid-like pattern;
• a plurality of image pixels formed in spaces between the grid-like pattern of the global vertical transfer gate structure, wherein each image pixel in the plurality of image pixels comprises:
• an inner photodiode;
• an outer photodiode, wherein the inner photodiode is laterally surrounded by the outer photodiode;
• a local vertical transfer gate structure formed between the inner photodiode and the outer photodiode;
• a first charge storage region that is coupled to the inner photodiode through the local vertical transfer gate structure;
• a second charge storage region that is coupled to the outer photodiode through the local vertical transfer gate structure;
• and
• a third charge storage region that is coupled to the outer photodiode through the global vertical transfer gate structure.