Linked Charge Storage Trenches for Image Sensor Dynamic Range
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Solution Overview
Problem
As CMOS pixel sizes decrease, the space for charge storage zones in image sensors is reduced, leading to a degradation of dynamic range and signal-to-noise ratio due to the limited capacity for storing charge carriers, and there is a challenge in extending the size of charge storage trenches without increasing time lag or losing the ability to read the entire storage zone.
Innovation Solution
The implementation of a pixel with charge storage structures comprising linked charge storage trenches and a linking channel that provides an electrostatic potential barrier, allowing for efficient charge storage and evacuation while maintaining a compact layout, including a 'T' or cross-shaped configuration of trenches and a transfer gate system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If the size of charge storage zones is reduced to accommodate smaller pixel dimensions, then the pixel density and resolution are improved, but the charge storage capacity is reduced leading to degradation of dynamic range and signal-to-noise ratio
Solution Approach 1:
The charge storage zone is divided into multiple separate trenches (first charge storage trench, second charge storage trench, and optionally third and fourth trenches) instead of using a single large trench. These segmented trenches are linked together through linking channels to form a distributed storage network that maintains high storage capacity within a compact area.
Solution Approach 2:
The linking channels are formed within the same substrate region as the charge storage trenches, effectively nesting the connection structure within the storage structure itself. This nested arrangement maximizes space utilization and allows multiple storage trenches to be interconnected without requiring additional lateral space.
2Quantity of substance
If the length of charge storage trenches is extended to increase storage capacity, then the charge storage capacity is improved, but the time lag for evacuating charge increases and the ability to read the entire storage zone is lost
Solution Approach 1:
The storage zone is segmented into multiple shorter trenches rather than one long trench. Each trench can be independently evacuated through its own transfer gate connection to the sense node, allowing parallel charge evacuation that reduces overall time lag while maintaining high storage capacity through the combined volume of multiple trenches.
Solution Approach 2:
Linking channels serve as intermediaries that connect multiple charge storage trenches to transfer gates and sense nodes. These intermediary structures enable efficient charge transfer from each segmented trench to the readout circuitry, ensuring that no portion of the storage zone is too far from an evacuation path.
3Quantity of substance
If multiple charge storage trenches are linked together to increase storage capacity, then the charge storage capacity is improved, but the device complexity increases
Solution Approach 1:
Multiple charge storage trenches and linking channels are merged into a unified charge storage structure that shares common doping regions and is controlled by coordinated transfer gates. This merging approach increases storage capacity while managing complexity through functional integration rather than completely separate components.
Solution Approach 2:
The linking channels serve multiple functions: they physically connect separate charge storage trenches, provide electrical isolation when needed, and enable charge transfer between trenches and to sense nodes. The transfer gates control multiple functions including charge transfer from photodiode to storage, evacuation from storage to sense node, and isolation during different operational phases.
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 enhances charge storage capacity without increasing the length of charge storage trenches, enabling effective charge evacuation during read phases and maintaining a compact pixel layout, thus improving the dynamic range and signal-to-noise ratio of image sensors.
Implementation Method 1
the linking channel provides an electrostatic potential barrier between the first and second charge storage trenches
Implementation Method 2
charge storage zones permit the storage of charge carriers from a photodiode
Data Source
AI summary
The invention concerns a pixel of an image array comprising one or more charge storage structures (200), each charge storage structure comprising: a first charge storage trench (202) doped to have a first conductivity type and having a first end (208) configured to receive charge accumulated by a photodiode; a second charge storage trench (204) doped to have the first conductivity type; and a first transfer gate (212) linking a second end (214) of the first charge storage trench (202) and the second charge storage trench (202, 204) to a sense node (216), wherein the first and second charge storage trenches are linked together by a linking channel (206) doped to have the first conductivity type and bordering a portion of an edge of the transfer gate (212).