Image sensor structure

A semiconductor device structure, comprising:

• a substrate comprising a plurality of photodiodes;
• a plurality of transfer gate transistors disposed over the substrate;
• a first dielectric layer over the substrate and the plurality of transfer gate transistors;
• a semiconductor layer disposed over the first dielectric layer;
• a plurality of source follower transistors, a plurality of row select transistors and a plurality of reset transistors disposed over the semiconductor layer;
• a second dielectric layer over the plurality of source follower transistors, the plurality of row select transistors and the plurality of reset transistors;
• and
• an interconnect structure disposed over the second dielectric layer,
• wherein each of the plurality of transfer gate transistors comprises a first channel area, each of the plurality of source follower transistors comprises a second channel area, each of the plurality of row select transistors comprises a third channel area, and each of the plurality of reset transistors comprises a fourth channel area,
• wherein the second channel area is greater than the first channel area, the third channel area or the fourth channel area.

A method, comprising:

• receiving a semiconductor substrate comprising a photodiode;
• forming a transfer gate transistor over the semiconductor substrate directly over the photodiode;
• depositing a first dielectric layer over the transfer gate transistor and the semiconductor substrate;
• depositing a semiconductor layer directly on the first dielectric layer;
• forming a source follower transistor, a row select transistor and a reset transistor over the semiconductor layer;
• forming a second dielectric layer over the source follower transistor, the row select transistor and the reset transistor;
• and
• forming an interconnect structure over the second dielectric layer.