Unit pixel of image sensor and photo detector thereof

1. A photo detector configured to absorb light in a unit pixel of an image sensor transforming the absorbed light to an electrical signal, comprising:

a light-absorbing part configured to absorb light by being formed in a floated structure;

an oxide film being in contact with one surface of the light-absorbing part;

a source being in contact with one side of the other surface of the oxide film and separated from the light-absorbing part with the oxide film therebetween;

a drain facing the source so as to be in contact with the other side of the other surface of the oxide film and separated from the light-absorbing part with the oxide film therebetween; and

a channel interposed between the source and the drain and configured to form flow of an electric current between the source and the drain,

wherein the light-absorbing part is doped with first type impurities, and the source and the drain are doped with second type impurities,

wherein the light-absorbing part is insulated from the source and the drain by the oxide film,

wherein electrons of electron-hole pairs generated by the absorbed light are moved to the source and the drain by a tunneling phenomenon occurred by an electric field concentrated in the oxide film, and the flow of the electric current of the channel is controlled by a change in the quantity of electric charge of the light-absorbing part caused by the moving of the electrons.

2. The photo detector of claim 1 , wherein the channel is formed in a state immediately before pinch-off by adjusting a W/L ratio, which is a ratio between a width (W) and a length (L) of the channel.

3. The photo detector of claim 1 , wherein the tunneling phenomenon is occurred in an area between one of the source and drain and the light-absorbing part.

4. The photo detector of claim 1 , wherein the source and the drain are formed by doping the second type impurities in a body, and the body is floated.

5. The photo detector of claim 1 , wherein a threshold voltage of the photo detector is changed due to the tunneling phenomenon occurred in the oxide film.

6. The photo detector of claim 1 , further comprising a light-blocking layer configured to block absorption of light in areas other than an upper surface of the light-absorbing part.