Image sensor integrated chip and method of forming the same

The present disclosure, in some embodiments, relates to an image sensor integrated chip. The image sensor integrated chip includes a substrate having a first side and a second side opposing the first side. The substrate has one or more sidewalls defining a trench extending along opposing sides of a pixel region having a first width. An isolation structure including one or more dielectric materials is disposed within the trench. The isolation structure has a second width. An image sensing element and a focal region are disposed within the pixel region. The focal region is configured to receive incident radiation along the second side of the substrate. A ratio of the second width to the first width is in a range of between approximately 0.1 and approximately 0.2, so that the focal region is completely confined between interior sidewall of the isolation structure facing the image sensing element.