Imaging Device by Buried Photodiode Structure

摘要

To achieve an image sensor with low noise, small dark current and the high sensitivity, an n-type region serving as a charge storage region ( 2 ) of a photodiode is buried in a substrate ( 1 ). The interface between silicon and a silicon oxide film ( 4 ) is covered with a p-layer ( 3 ) of high concentration, and a p-layer ( 11 ) of a relatively low concentration is formed only in the portion immediately below a floating electrode ( 14 ) for signal extraction. The electrons generated by light are stored in the n-type region serving as the charge storage region ( 2 ), and the potential of the portion of the p-layer ( 11 ) at the surface of the semiconductor region is changed thereby. The change in the potential is transmitted through a thin insulating film to the floating electrode ( 14 ) in a floating state by the capacitive coupling. The change in the potential of the floating electrode ( 14 ) is read out by a buffer transistor ( 7 ). The initialization of charges is executed by adding a positive high voltage to the gate electrode ( 6 ) of a first transfer transistor ( 21 ) by a control signal R, such that all of the electrons stored in the charge storage region ( 2 ) can be transferred to the n⁺ region ( 5 ), and the generation of the reset noise can be protected.