Abstract
An active pixel sensor includes a substrate, a photo-sensing region, a peripheral circuit region, and an isolation region. The photo-sensing region and the peripheral circuit region are formed on the substrate. The isolation region is formed between the photo-sensing region and the peripheral circuit region for isolating the photo-sensing region and the peripheral circuit region. The photo-sensing region induces photo current according to the received light. The peripheral circuit region includes a first transistor having a source connected to a bit line, a second transistor having a gate connected to the photo-sensing region, a source connected to the drain of the first transistor and a drain connected to a voltage source, and a third transistor having a source connected to the photo-sensing region and a drain connected to the voltage source.