Overflow Image Sensor Pixel With Dual Anti-Blooming Implants
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Solution Overview
Problem
Existing image sensor pixels face challenges in managing overflow blooming charge, particularly under extreme light conditions, where anti-blooming implants are insufficient, leading to undesirable image artifacts.
Innovation Solution
The implementation of a dual anti-blooming implant structure, where a first anti-blooming implant is coupled to the photodetector and floating diffusion, and a second anti-blooming implant is coupled to the photodetector and voltage source contact, with the second implant having a greater potential barrier than the first, to effectively redirect blooming charge, thereby reducing image artifacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a dedicated anti-blooming gate is used to handle overflow blooming, then blooming charge handling capability is improved, but area overhead increases and photodetector dark signal non-uniformity degrades
Solution Approach 1:
The patent divides the anti-blooming function into two separate implants rather than using a single dedicated anti-blooming gate. The first anti-blooming implant handles normal blooming conditions, while the second anti-blooming implant handles overflow blooming conditions. This segmentation allows the system to achieve overflow blooming handling capability without requiring a dedicated anti-blooming gate, thereby avoiding the associated area overhead and dark signal non-uniformity degradation.
Solution Approach 2:
The dual anti-blooming implant structure provides multi-functionality by handling both normal and overflow blooming conditions within the same pixel structure. The first implant operates under normal conditions while the second implant activates under extreme light conditions, eliminating the need for separate dedicated anti-blooming gates for different blooming scenarios.
2Device complexity
If a single anti-blooming implant is used, then device complexity is reduced, but overflow blooming charge handling capability is insufficient under extreme light conditions
Solution Approach 1:
The patent segments the anti-blooming function into two distinct implants with different potential barriers. The first anti-blooming implant has a lower potential barrier for normal operation, while the second anti-blooming implant has a higher potential barrier that activates under extreme light conditions. This segmentation enables the system to handle overflow blooming charge without significantly increasing device complexity, as both implants are integrated into the existing pixel structure.
Solution Approach 2:
The patent changes the potential barrier parameter between the two anti-blooming implants to handle different blooming conditions. The second anti-blooming implant is configured with a higher potential barrier than the first, allowing it to handle overflow blooming charge under extreme light conditions while the first implant handles normal conditions. This parameter change enables enhanced overflow blooming handling capability without requiring a complete redesign of the implant structure.
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 dual anti-blooming implant configuration enhances the handling of overflow blooming charge, minimizing image artifacts and maintaining photodetector dark signal uniformity, even under high light intensity conditions.
Implementation Method 1
a photodetector positioned in a semiconductor substrate that generates a charge in response to incident light
Implementation Method 2
the first anti-blooming implant at least partially overlaps the transfer gate; and a second anti-blooming implant positioned in the semiconductor substrate, wherein the second anti-blooming implant is coupled to the photodetector and a voltage source contact to transfer the blooming charge generated by the photodetector to the voltage source contact
Data Source
AI summary
Anti-blooming control in overflow image sensor pixel. At least one example is an image sensor pixel comprising: a photodetector positioned in a semiconductor substrate; a gate oxide layer positioned on the semiconductor substrate; a floating diffusion; a transfer gate positioned on the gate oxide layer; a first anti-blooming implant positioned in the semiconductor substrate, wherein the first anti-blooming implant is coupled to the photodetector and the floating diffusion; and a second anti-blooming implant positioned in the semiconductor substrate, wherein the second anti-blooming implant is coupled to the photodetector and a voltage source contact.