US Patent 7115924 Pixel with asymmetric transfer gate channel doping

A pixel including a substrate of a first conductivity type, a photodetector of a second conductivity type that is opposite the first conductivity type and configured to convert incident light to a charge, a floating diffusion of the second conductivity, and a transfer region between the photodetector and floating diffusion. A gate is formed above the transfer region and partially overlaps the photodetector and is configured to transfer charge from the photodetector to the floating diffusion. A pinning layer of the first conductivity type extends at least across the photodetector from the gate. A channel region of the first conductivity type extends generally from a midpoint of the gate at least across the photodiode and is formed by an implant of a dopant of the first conductivity and having a concentration such that a dopant concentration of the transfer region is greater proximate to the photodetector than proximate to the floating diffusion.