an image sensor includes a substrate having adjacent pixel regions and respective photodiode regions therein , and a pixel separation portion including a trench extending into the substrate between the adjacent pixel regions . the trench includes a conductive common bias line therein and an insulating device isolation layer between the common bias line and surfaces of the trench . a conductive interconnection is coupled to the common bias line and is configured to provide a negative voltage thereto . related fabrication methods are also discussed .