CMOS Pixel Isolation Structure for Charge Transfer and Full Well Capacity
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Solution Overview
Problem
Current CMOS image sensors face challenges in improving charge transfer characteristics and charge storage capacity of unit pixels, which are crucial for high-performance imaging applications.
Innovation Solution
The design incorporates a substrate with adjacent photoelectric conversion regions and a deep device isolation pattern that includes extensions between and within these regions, along with multiple transfer gate electrodes to enhance charge transfer and storage capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional CMOS image sensor structure is used, then the device complexity is low and manufacturing is easier, but the charge transfer characteristics and charge storage capacity are insufficient
Solution Approach 1:
The pixel region is divided into multiple photoelectric conversion regions (first, second, third, and fourth regions) with different depths and functions. Each region is segmented to perform specific tasks: some regions are optimized for charge generation while others are optimized for charge storage and transfer. This segmentation allows simultaneous improvement of charge transfer characteristics and storage capacity without requiring a completely new device architecture.
Solution Approach 2:
The invention introduces depth dimensionality by creating photoelectric conversion regions at different depths within the substrate. The deep photoelectric conversion regions extend deeper into the substrate compared to shallow regions, creating a three-dimensional structure. This depth differentiation enables multiple charge storage nodes at various depths, improving charge storage capacity while maintaining efficient charge transfer pathways from shallower to deeper regions.
2Quantity of substance
If the photoelectric conversion regions are enlarged to increase charge storage capacity, then the charge storage capacity improves, but the area available for other pixel components decreases
Solution Approach 1:
The invention implements a nested structure where deep photoelectric conversion regions are positioned within the substrate volume beneath shallower regions. The first and second photoelectric conversion regions are nested above the third and fourth regions, creating a vertical stacking arrangement. This nesting allows the pixel to store charges in multiple depth levels without increasing the planar footprint, effectively increasing charge storage capacity within the same pixel area.
Solution Approach 2:
By transitioning from a two-dimensional planar structure to a three-dimensional vertical structure, the invention increases charge storage capacity through the depth dimension. Multiple photoelectric conversion regions are stacked vertically at different depths, allowing the pixel to accumulate more charges without expanding the horizontal pixel area. This vertical stacking enables higher charge storage capacity while maintaining compact pixel dimensions.
3Quantity of substance
If deep photoelectric conversion regions are introduced to improve charge storage, then the charge storage capacity increases, but the manufacturing precision requirements increase
Solution Approach 1:
The deep photoelectric conversion regions are segmented into discrete, separately-formed regions (third and fourth regions) that can be independently controlled during manufacturing. By dividing the deep structure into distinct segments rather than a single continuous deep region, the invention reduces the cumulative depth control error and allows for more precise manufacturing of each individual region's depth and position.
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 improves charge transfer characteristics and increases the charge storage capacity of unit pixels, leading to enhanced imaging performance.
Implementation Method 1
Each of the pixels may include a photodiode (PD). The photodiode may convert incident light into an electrical signal.
Data Source
AI summary
An image sensor includes a substrate including a pixel region, the substrate extending in a first direction and a second direction intersecting the first direction, first and second photoelectric conversion regions disposed in the pixel region and adjacent to each other in a first direction, a deep device isolation pattern penetrating the substrate in a third direction perpendicular to the first and second directions, and surrounding the pixel region, the deep device isolation pattern comprising first extensions extending in the second direction between the first and second photoelectric conversion regions, the first extensions spaced apart from each other in the second direction, a plurality of first transfer gate electrodes vertically overlapping with the first photoelectric conversion region, and a plurality of second transfer gate electrodes vertically overlapping with the second photoelectric conversion region. The first photoelectric conversion region extends in the second direction under the plurality of first transfer gate electrodes.