An image sensor with passivated full deep-trench isolation includes a semiconductor substrate, the substrate including a plurality of sidewalls that form a plurality of trenches that separates pixels of a pixel array, and a passivation layer lining the plurality of sidewall surfaces and the back surface of the semiconductor substrate. A method for forming an image sensor with passivated full deep-trench isolation includes forming trenches in a semiconductor substrate, filling the trenches with a sacrificial material, forming a plurality of photodiode regions, forming a circuit layer, thinning the semiconductor substrate, and removing the sacrificial material. A method for reducing noise in an image sensor includes removing material from a semiconductor substrate to form a plurality of trenches that extend from a front surface toward a back surface, and depositing a dielectric material onto the back surface and into the plurality of trenches through a back opening of each trench.