In a solid-state imaging device having photoelectric conversion units arranged in the form of a matrix in an imaging region, an optical black region (hereinafter referred to as “OB region”) is provided at the periphery of the imaging region. The OB region is formed by light-shielded photoelectric conversion units disposed in the peripheral region. The OB region is shielded from light using a light-shielding film for covering transfer electrodes disposed beside the photoelectric conversion units and transfer wirings connected to the electrodes. The light-shielding film has pixel openings at which only the tops of the photoelectric conversion units in the imaging region are exposed.
The OB region must be reliably shielded from light to set a proper reference for black levels output from pixels. However, it is known that sufficient light-shielding performance is not provided by a light-shielding film as described above alone.
Under the circumstance, light-shielding performance sufficient for the OB region is achieved by shielding the OB region further by using wirings for peripherals circuits laid outside the OB region.
Another proposed solution is to use a light-shielding film made of a conductive material and having a structure formed by two layers electrically isolated from each other by an insulation layer interposed between them. The film serves as a double shield covering only an OB region to minimize smear on a reference signal for an optical black level attributable to electric charges (see JP-A-2009-70912 (in particular, paragraph 0037) (Patent Document 1))
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