Pixel with asymmetric transfer gate channel doping

Abstract

A pixel including a substrate of a first conductivity type and having a surface, a photodetector of a second conductivity type that is opposite the first conductivity type, a floating diffusion region of the second conductivity type, a transfer region between the photodetector and the floating diffusion, a gate positioned above the transfer region and partially overlapping the photodetector, and a pinning layer of the first conductivity type extending at least across the photodetector from the gate. A channel implant of the first conductivity type extending from between a midpoint of the transfer gate and the floating diffusion to at least across the photodiode and having a dopant concentration such that a dopant concentration of the transfer region is greater proximate to the photodetector than the floating diffusion, and wherein a peak dopant concentration of the channel implant is at a level and at a depth below the surface such that a partially-buried channel is formed in the transfer region between the photodiode and floating diffusion when the transfer gate is energized.