Transistor having increased effective channel width

A method of manufacturing a transistor for an image sensor, comprising:

• providing a substrate material;
• forming an isolation layer on the substrate material;
• forming a recess to a first depth in the substrate material, the recess corresponding to a gate region and extending in a channel length direction and a channel width direction that is perpendicular to the channel length direction;
• forming a trench structure in the substrate material by deepening the recess to a second depth using an isotropic process;
• forming a gate portion of the isolation layer on the substrate material such that the gate portion of the isolation layer extends into the trench structure;
• and
• forming a gate on the isolation layer such that the gate extends into the trench structure.