Solid-state image sensor and method for producing the same

Abstract

A floating diffusion () is created substantially at center of the light-receiving surface of an embedded photodiode (), with a gate electrode of a transfer transistor () surrounding the floating diffusion. The concentration (or depth) of impurities in a p-type semiconductor region, n-type semiconductor region or p-well region is changed in an inclined form so that a potential gradient being inclined downwards from the circumference to the center is created when an appropriate bias voltage is applied to the pn junction. The photocharges produced by incident light are rapidly moved along the potential gradient toward the center. Even in the case where the photocharge storage time is short, the photocharges can be efficiently collected since the maximum moving distance from the circumference of the photodiode () to the floating diffusion (). Thus, the photocharges produced by the photodiode () are efficiently utilized, whereby the detection sensitivity is improved.