Double Vertical Transfer Gate Doping Profile for Image Sensors
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Solution Overview
Problem
Backside illumination semiconductor image sensors face challenges in optimizing operating voltage, carrier loss, and response time due to the limitations of conventional single vertical transfer gates in photodetectors.
Innovation Solution
The implementation of double vertical transfer gates with varying doping levels, where the layers closer to the backside have a lower doping level and those nearer the front side have a higher doping level, forming a potential barrier to enhance charge transfer efficiency and reduce carrier loss, thereby optimizing operating voltage and response time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional single vertical transfer gate is used in a backside illumination semiconductor image sensor, then the device complexity is reduced, but the operating voltage efficiency deteriorates and carrier loss increases
Solution Approach 1:
The single vertical transfer gate is segmented into multiple doping regions (first doped region, second doped region, third doped region) with different doping levels. This segmentation allows each region to perform specific functions in the charge transfer process, improving operating voltage efficiency while maintaining reasonable device complexity.
Solution Approach 2:
Different doping levels are applied to different regions of the vertical transfer gate. The first doped region has a first doping level, the second doped region has a second doping level, and the third doped region has a third doping level. This local quality variation optimizes the potential barrier formation and charge transfer efficiency at each location.
2Device complexity
If a conventional single vertical transfer gate is used, then the device complexity is reduced, but carrier loss increases
Solution Approach 1:
The vertical transfer gate is divided into multiple doped regions with different doping levels to create optimized potential barriers. This segmentation reduces carrier loss by preventing carrier diffusion into adjacent regions while maintaining efficient charge transfer through the structured doping profile.
Solution Approach 2:
The doping level parameter is varied across different regions of the vertical transfer gate. By changing the doping level from the first doped region to the second and third doped regions, the potential barrier characteristics are optimized to reduce carrier loss while maintaining transfer efficiency.
3Device complexity
If a conventional single vertical transfer gate is used, then the device complexity is reduced, but the response time deteriorates
Solution Approach 1:
The vertical transfer gate is segmented into multiple doped regions that work in sequence during charge transfer. This segmentation creates optimized electric field distributions that accelerate charge carrier transport, reducing the response time while maintaining a manageable structural complexity.
Solution Approach 2:
Different doping levels in different regions create localized electric field enhancements that accelerate charge transfer. The second doped region with its specific doping level creates optimal conditions for rapid charge transfer, reducing the overall response time of the image sensor.
4Use of energy by moving object
If multiple doped regions with varying doping levels are implemented, then operating voltage efficiency is improved, but device complexity increases
Solution Approach 1:
Multiple doped regions with different doping levels are merged into a single vertical transfer gate structure. This combining approach achieves the benefits of complex doping profiles while maintaining a unified device structure, balancing operating voltage efficiency with device complexity.
Solution Approach 2:
The vertical transfer gate with multiple doped regions serves multiple functions: charge transfer, potential barrier formation, and carrier loss prevention. This multi-functionality justifies the increased structural complexity by delivering multiple performance benefits from a single integrated 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 configuration improves the operating voltage efficiency, reduces carrier loss, and enhances the response time of the image sensor, leading to improved image quality and performance.
Implementation Method 1
An image sensor may use a photoelectric effect to absorb and convert light to an electron-hole pair at each of the photodetectors
Implementation Method 2
The implementation of double vertical transfer gates with varying doping levels, where the layers closer to the backside have a lower doping level and those nearer the front side have a higher doping level, forming a potential barrier to enhance charge transfer efficiency
Data Source
AI summary
In an embodiment, an image sensor includes a semiconductor region, a first doped region disposed over the semiconductor region, a ring shaped well disposed over the first doped region and surrounding parts of the first doped region, a second doped region formed within the ring shaped well and disposed over the first doped region, and a third doped region disposed over the second doped region. The ring shaped well is defined by a conductor surrounded by an insulator. The conductor is connected to a voltage terminal. The third doped region is more heavily doped than the second doped region, which is more heavily doped than the first region, and are all of the same doping type. The first doped region and the second doped region within the ring shaped well, form a potential barrier for controlling transfer of charge carriers from the first doped region to the third doped region.