Patent ID: 8228409

Claim:
An image sensor comprising: a readout circuitry formed on a first substrate; an inter-layer dielectric layer formed on the first substrate; a metal line formed in the inter-layer dielectric layer such that the metal line is electrically connected with the readout circuitry; a plurality of contact plugs formed on the metal line; an image sensing device formed on the plurality of contact plugs, wherein the image sensing device is electrically connected to the metal line through the plurality of contact plugs; and an electric junction area formed on the first substrate such that the electric junction area is electrically connected with the readout circuitry and electrically connects the metal line to the readout circuitry; wherein the readout circuitry comprises a transistor, wherein a potential difference is made between a source and a drain of the transistor, the electric junction area being at the source of the transistor, wherein the transistor is a transfer transistor, and wherein the potential difference is made by an ion implantation concentration of the source of the transistor being lower than ion implantation concentration of a floating diffusion area at the drain of the transistor.