A backside-illuminated multi-collection-gate image sensor is expected to achieve ultra-high-speed imaging. Signal electrons generated by incident light are collected to the pixel center of the front side and distributed to multiple collection gates placed around the center at a very short time interval. The temporal resolution is measured by the spread of arrival times of signal electrons to a collection gate. The major cause of the spread is mixing of signal electrons generated near the pixel border travelling a longer horizontal distance to the pixel center and those generated near the pixel center. Suppression of the horizontal travel time effectively decreases the standard deviation of the distribution of the arrival time. Therefore, devices to suppress the effects of the horizontal motion are introduced, such as a pipe-like photoelectron conversion layer with a much narrower cross section than the pixel area and a funnel-like photoelectron conversion layer.