CMOS Pixel Isolation Layout for Charge Transfer and Storage
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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 includes a substrate with adjacent photoelectric conversion regions and a deep device isolation pattern with extensions, along with multiple transfer gate electrodes, to enhance charge transfer and storage capacity. This configuration allows for improved charge handling and transfer efficiency within each pixel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional deep device isolation pattern is used without extensions, then the device structure is simpler, but the charge transfer characteristics and charge storage capacity of unit pixels are insufficient
Solution Approach 1:
The deep device isolation pattern is segmented by introducing first extensions that divide the isolation region between adjacent photoelectric conversion regions. These extensions create separate isolation zones that improve charge transfer characteristics by preventing charge leakage while maintaining structural organization. The segmentation of the isolation pattern directly addresses the charge transfer reliability issue without requiring complete redesign of the entire device architecture.
Solution Approach 2:
The first extensions of the deep device isolation pattern extend in the second direction (horizontal direction) between adjacent photoelectric conversion regions, adding a dimensional element to the traditionally vertical isolation structure. This dimensional enhancement creates additional charge transfer pathways and improves isolation effectiveness without significantly increasing overall device complexity.
2Area of stationary object
If photoelectric conversion regions are placed closer together to increase pixel density, then the device area efficiency improves, but charge leakage between regions increases
Solution Approach 1:
The first extensions of the deep device isolation pattern segment the space between adjacent photoelectric conversion regions, creating distinct isolation zones that prevent charge leakage. These extensions divide the potentially harmful continuous isolation region into segmented zones that actively block charge carrier migration between pixels, enabling closer placement of photoelectric conversion regions without compromising charge isolation.
Solution Approach 2:
The first extensions act as intermediary structures between adjacent photoelectric conversion regions, providing a physical barrier that mediates the interaction between neighboring pixels. These extensions serve as charge blocking intermediaries that prevent direct charge leakage pathways while allowing the photoelectric conversion regions to be positioned closer together for improved area efficiency.
3Reliability
If multiple transfer gate electrodes are disposed on photoelectric conversion regions, then charge transfer characteristics improve, but the device complexity increases
Solution Approach 1:
The first extensions of the deep device isolation pattern serve multiple functions: they provide charge isolation, define pixel boundaries, and act as structural support for transfer gate electrodes. By making the isolation pattern multi-functional, the design reduces the need for separate dedicated structures, thereby improving charge transfer characteristics without proportionally increasing device complexity.
Solution Approach 2:
The transfer gate electrodes are merged with the deep device isolation pattern structure, where the first extensions serve as both isolation barriers and structural foundations for the transfer gates. This merging of functions allows multiple transfer gate electrodes to be disposed on photoelectric conversion regions with improved charge transfer characteristics while minimizing the increase in overall device complexity through shared structural elements.
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
The solution effectively enhances the charge transfer characteristics and increases the charge storage capacity of unit pixels, leading to improved imaging performance and efficiency in CMOS image sensors.
Implementation Method 1
Each of the pixels may include a photodiode (PD). The photodiode may convert incident light into an electrical signal.
Data Source
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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.