There is provided a structure to improve BSI global shutter efficiency. In a sensor pixel circuit, at least one strong electric field is formed at the position of a floating diffusion region to accordingly have the effect of shielding the floating diffusion region. Or, the semiconductor material from the floating diffusion node toward a light incident direction is removed in the manufacturing process such that a depletion region cannot be formed in this direction. Or, a reflection layer or a photoresist layer is formed in the light incident direction to block the light. In these ways, charges generated by the undesired noises are reduced, and noise charges are difficult to reach the floating diffusion region thereby improving the shutter efficiency.