Vertical transfer gate doping distribution for charge transfer from a photodiode

A pixel cell, comprising:

• a photodiode disposed in a semiconductor material;
• a floating diffusion disposed in the semiconductor material;
• a transfer gate comprising a vertical transfer gate structure disposed in the semiconductor material between the photodiode and the floating diffusion, the transfer gate coupled between the photodiode and the floating diffusion;
• and
• a passivation layer disposed in the semiconductor material and proximate to the vertical transfer gate, wherein the passivation layer comprises doped material in the semiconductor material proximate to the vertical transfer gate and having a region with a non-uniformly distributed doping profile proximate to the vertical gate structure such that a first doping concentration of the region in the passivation layer proximate to the vertical gate structure along a first direction is less than a second doping concentration of the region in the passivation layer proximate to the vertical gate structure along a second direction, and wherein the doped material comprises:
• a first doped region having the first doping concentration and surrounding the vertical transfer gate in the semiconductor material, wherein the first doped region has a first oval shaped profile with a major axis that intersects a charge transfer path between the photodiode and the floating diffusion;
• and
• a second doped region having the second doping concentration and surrounding the vertical transfer gate in the semiconductor material, wherein the second doped region has a second oval shaped profile with a major axis that is parallel with charge transfer path, and wherein the second doping concentration is greater than the first doping concentration.

An imaging system, comprising:

• a pixel array having a plurality of pixel cells, each of the plurality of pixel cells comprising:
• a floating diffusion disposed in a semiconductor material,
• four pixels, each pixel comprising:
• a photodiode disposed in a semiconductor material;
• and
• a transfer gate comprising a vertical transfer gate structure disposed in the semiconductor material between the photodiode and the floating diffusion,
• wherein the four pixels are coupled to the floating diffusion, and wherein at least two of the pixels have a different first direction and a different second direction, and
• a passivation layer disposed in the semiconductor material and proximate to the vertical transfer gate, wherein the passivation layer has a region with a non-uniformly distributed doping profile proximate to the vertical gate structure such that a first doping concentration of the region in the passivation layer proximate to the vertical gate structure along a first direction is less than a second doping concentration of the region in the passivation layer proximate to the vertical gate structure along a second direction;
• and
• control circuitry coupled to the pixel array to control operation of the pixel array.