CMOS Image Sensor Source Follower Gate Length Noise Reduction
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Solution Overview
Problem
Current image sensors face challenges in reducing noise, particularly due to random charge trapping and de-trapping in the channel of the source follower transistor, which affects the quality of electrical signals converted from optical images.
Innovation Solution
The design incorporates a CMOS image sensor with specific transistor gate configurations, including a source follower gate with a greater length than reset and selection gates, and strategically placed dopant regions and interconnection conductors to minimize noise caused by charge fluctuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the source follower gate length is increased to reduce noise from charge trapping and de-trapping, then the noise level decreases and signal quality improves, but the transistor area increases and device integration density decreases
Solution Approach 1:
The patent applies local quality by making the source follower gate length different from other transistor gates. Specifically, the source follower gate has a longer length than the reset gate and selection gate, creating a localized structural variation that针对性地 addresses noise reduction in the source follower transistor while maintaining standard dimensions for other transistors. This localized modification optimizes the specific region where charge trapping effects are most problematic.
2Reliability
If dopant regions are strategically placed to minimize charge fluctuations, then charge transfer efficiency improves and noise is reduced, but the manufacturing process complexity increases
Solution Approach 1:
The patent implements preliminary action by pre-positioning dopant regions in specific locations within the pixel structure before final device assembly. The dopant regions are strategically placed in the substrate adjacent to the photoelectric conversion layer and transfer gate, creating a predetermined charge distribution that facilitates efficient charge transfer and minimizes fluctuations during operation. This pre-configuration ensures optimal charge management from the outset.
3Productivity
If the photoelectric conversion layer is optimized for higher quantum efficiency, then more charge carriers are generated, but the device becomes more sensitive to charge trapping effects that cause noise
Solution Approach 1:
The patent introduces an intermediary structure in the form of strategically placed dopant regions that act as a mediator between the photoelectric conversion layer and the transfer gate. These dopant regions create a controlled charge environment that facilitates smooth charge carrier transport while mitigating the impact of charge trapping effects. The intermediary dopant regions buffer the interaction between generated charges and potential trapping sites, allowing high quantum efficiency to be maintained without proportionally increasing noise susceptibility.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration reduces noise associated with charge trapping and de-trapping, enhancing the quality of electrical signals converted from optical images and improving overall image sensor performance.
Implementation Method 1
a photoelectric conversion layer (110) in the substrate and having a first conductivity type
Data Source
AI summary
A CMOS image sensor includes a substrate and at least one device isolation region in the substrate and defining first and second pixel regions and first and second active portions in each of the first and second pixel regions. A reset and select transistor gates are disposed in the first pixel region, while a source follower transistor gate is disposed in the second pixel region, such that pixels in the first and second pixel regions share the reset, select and source follower transistors. A length of the source follower transistor gate may be greater than lengths of the reset and selection transistor gates.