Isolation structures for semiconductor devices including trenches containing conductive material

An isolation structure formed in a semiconductor substrate of a first conductivity type includes a floor isolation region of a second conductivity type opposite to the first conductivity type submerged in the substrate. A first trench extends downward from a surface of the substrate and overlaps onto the floor isolation region. The first trench includes walls lined with a dielectric material and contains a conductive material. The first trench and the floor isolation region electrically isolate a pocket of the first conductivity type from the substrate.