Low dark current CMOS image sensor pixel with photodiode structure enclosed by P-well

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A low dark current CMOS image sensor pixel which can be easily implemented using a standard CMOS technology without any process modification is presented. Dark current is mainly generated from the interface region between the shallow trench isolation (STI) and the active region. The proposed pixel can reduce dark current by separating the STI region from a photodiode, using a simple layout modification to enclose the photodiode junction with the P-well. A test sensor array has been fabricated using 0.18 µm standard CMOS process and its performance characterised. The dark current of the proposed pixel has been measured as 0.93fA/pixel, which is by a factor of two smaller than that of the conventional design.