Method and structure for reducing leakage currents of active area diodes and source/drain diffusions

A fabrication method for providing isolation between adjacent regions of an integrated circuit (10) includes providing a guard layer (40; 68; 72; 88; 90; and 128) over field edges that are the interfaces between field oxide regions (30; 54; and 92) and diffusion regions (14; 26; 52; 86; and 96) in which dopant is introduced. The guard layer will inhibit introduction of dopant along the field-edge, so that a substantially dopant-free transition strip (42; 70; and 130) is formed. The transition strip inhibits current leakage from the active region to the field oxide region. In one embodiment, the active region is an active area diode, such as used to form an Active Pixel Sensor (APS) pixel. The guard layer is biased so as to further inhibit current leakage during circuit operation. In another embodiment, the method is used in the fabrication of transistors for APS pixels having an overlay photodiode structure.