Variable Gate Oxide Thickness for Image Sensor Charge Transfer

The patent applies local quality by using a graded doping concentration profile where the dopant concentration varies spatially across the channel region. The doping concentration is higher near the floating diffusion region and lower near the photosensitive element, creating a lateral electric field that accelerates electrons without significantly diffusing into the photosensitive element. This localized variation in dopant concentration optimizes charge transfer speed in the channel while preserving full well capacity in the photosensitive element.

The patent applies parameter changes by modifying the doping concentration parameter across the channel region. The graded doping profile creates a continuously varying electric field that provides the necessary lateral field for electron acceleration while avoiding the formation of a potential energy barrier. The doping concentration is carefully controlled to decrease toward the photosensitive element, ensuring that electrons can be accelerated through the channel without encountering a blocking potential barrier, thus achieving both fast and complete charge transfer.

The patent applies local quality by implementing a gate oxide with non-uniform thickness where the oxide thickness varies across the transfer gate region. The gate oxide is thinner in regions where stronger electric fields are needed to accelerate electrons and complete charge transfer, while being thicker in other regions. This spatial variation in oxide thickness creates the necessary electric field distribution to eliminate image lag while maintaining manufacturability through standard semiconductor fabrication processes.