Solid-state imaging device, method of driving the same, and electronic system including the device

A solid-state imaging device comprising:

• a unit pixel including (a) a photoelectric conversion section, (b) a floating diffusion section including (i) an impurity-diffusion region in a well of a first conductivity type and capable of temporarily accumulating or holding electric charges generated by the photoelectric conversion section and (ii) a sub-region at least partially in the impurity-diffusion region, and (c) a reset transistor that resets the impurity-diffusion region by using a voltage of a voltage-supply line, the sub-region having an impurity concentration such that at least a part of the impurity-diffusion region is enabled to achieve a depletion state;
• wherein,
• the sub-region is located at a side of the impurity-diffusion region that is closest to the reset transistor,
• a surface of the floating diffusion section that is exposed from the well includes a surface of the impurity-diffusion region and a surface of the sub-region,
• the impurity-diffusion region and the sub-region are of a second conductivity type opposite the first conductivity type, and
• the impurity concentration of the sub-region is less than that of the impurity-diffusion region.