Pixel structure of an image sensor and fabrication method thereof

A pixel structure of an image sensor and fabrication methods thereof are provided. The pixel structure includes a semiconductor substrate and plural pixel units disposed on the semiconductor substrate. The pixel units are electrically connected to each other, and each of the pixel units includes a light-sensitive region, a transfer gate and a protection layer. A terminal portion of the protection layer is covered by the transfer gate, and a width of the terminal portion of the protection layer is progressively decreased along a depthwise direction of the terminal portion of the protection layer. In the fabrication methods of the pixel structure, the protection layers of the pixel units are formed by doping with a tilt angle, so as to form the terminal portion of the protection layer.