Patent ID: 8809925

Claim:
An image sensor pixel, comprising: a photosensitive element disposed in a substrate layer for accumulating an image charge in response to light; a floating diffusion (“FD”) region disposed in the substrate layer to receive the image charge from the photosensitive element; and a transfer device disposed between the photosensitive element and the FD region to selectively transfer the image charge from the photosensitive element to the FD region, the transfer device including: a gate disposed between the photosensitive element and the floating diffusion region; a buried channel dopant region disposed adjacent to the FD region and underneath the gate; and a surface channel region disposed between the buried channel dopant region and the photosensitive element and disposed underneath the gate, wherein a ratio of a length of the buried channel dopant region and a length of the surface channel region is tuned to allow electrons from the photosensitive element to punch through to the buried channel dopant region when the photosensitive element approaches full capacity and the transfer device is off.