In this article the authors propose a novel T-shaped shallow-trench isolation (STI) technology including an unfilled floating void STI. The structure aims to reduce the dark current in complementary metal oxide semiconductor active-pixel sensor technology and is optimized with respect to the size of the depletion region surrounding the STI, also accounting for the fringe electric field and the leakage current. Simulations indicate that a large air void positioned far from the bottom and top of the T-shaped trench improves performance. (C) 2009 American Vacuum Society. [DOI: 10.1116/1.3074346]