Image sensor including floating diffusion region

An image sensor comprising:

• unit pixels arranged in a matrix having two rows and two columns, each of the unit pixels including:
• a photodiode in a substrate, the photodiode being doped with n-type impurities;
• a pair of vertical transfer gates on the photodiode, each of the pair of vertical transfer gates extending through a portion of the substrate;
• and
• a floating diffusion region at an upper portion of the substrate between the pair of vertical transfer gates, the floating diffusion region including first impurities;
• a pad structure on the floating diffusion regions of the unit pixels;
• and
• a contact plug contacting an upper surface of the pad structure,
• wherein:
• the unit pixels form a pixel group,
• the floating diffusion regions of the unit pixels are connected to one another at a center of the pixel group to form a common floating diffusion region, and
• the common floating diffusion region including the first impurities.

An image sensor comprising:

• a substrate having a pixel group, the pixel group including unit pixels arranged in a matrix having two rows and two columns;
• a pad structure on the substrate, the pad structure including a first central portion and first, second, third and fourth extension portions, the first central portion being disposed at a center of the pixel group of the substrate in a plan view, and the first, second, third and fourth extension portions extending from the first central portion toward centers of the unit pixels, respectively, of the substrate in a plan view, and the pad structure including polysilicon doped with first impurities;
• and
• a common floating diffusion region at an upper portion of the substrate overlapping the pad structure in a vertical direction substantially perpendicular to an upper surface of the substrate, the common floating diffusion region including the first impurities,
• wherein each of the unit pixels includes:
• a photodiode in the substrate, the photodiode being doped with n-type impurities;
• and
• a pair of vertical transfer gates on the photodiode, each of the pair of vertical transfer gates extending through a portion of the substrate.