The present disclosure provides a device having a doped active region disposed in a substrate. The doped active region having an elongate shape and extends in a first direction. The device also includes a plurality of first metal gates disposed over the active region such that the first metal gates each extend in a second direction different from the first direction. The plurality of first metal gates includes an outer-most first metal gate having a greater dimension measured in the second direction than the rest of the first metal gates. The device further includes a plurality of second metal gates disposed over the substrate but not over the doped active region. The second metal gates contain different materials than the first metal gates. The second metal gates each extend in the second direction and form a plurality of respective N/P boundaries with the first metal gates.