Patent ID: 7420233

Claim:
An image pixel structure, comprising: a semiconductor substrate of a first conductivity type having a surface; a gate over said surface of the substrate; a floating diffusion region within said substrate; a channel region under said gate; and a photodiode within said substrate, said photodiode including a substrate region of said first conductivity type and an implant region of a second conductivity type, said substrate region and implant region forming a junction for generating charge in response to light, said implant region including: a first portion extending underneath a majority of said junction, having a lower boundary in said substrates, and extending further towards a region of said substrate beneath said gate than a second portion of said implant region extends towards said region beneath said gate, said second portion adjacent to and substantially underneath said first portion such that said lower boundary of said first portion forms an upper boundary for at least a part of said second portion, said second portion extending underneath a majority of said junction, and a third portion extending further towards said region of substrate beneath said gate than said first and second portions extend toward said region beneath said gate to increase charge transfer from said implant region to said floating diffusion region when said gate is switched on and having a donor concentration of said second conductivity type less than said first and second portions to reduce short-channel effects or punch-through between said implant region and floating diffusion region when said gate is switched off.