Image Sensor Floating Diffusion Channel Region Design
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current image sensors face challenges in achieving improved performance and efficiency due to limitations in the design and fabrication of photodiodes and transfer transistors, which affect the conversion of optical images into electric signals.
Innovation Solution
The method involves forming first and second photodiodes within a substrate, with gate electrodes partially overlapping the photodiodes, and creating impurity injection regions using n-type and p-type impurities to form a floating diffusion region and channel region, where the channel region surrounds the floating diffusion region and has a higher p-type impurity concentration, enhancing thermal diffusivity and reducing leakage current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional photodiode and transfer transistor design is used, then manufacturing simplicity is maintained, but operating speed and image quality are limited
Solution Approach 1:
The pixel structure is segmented into distinct functional regions: photodiode region for light detection, transfer transistor region for charge transfer, and floating diffusion region for signal readout. This segmentation allows each component to be optimized independently, improving overall operating speed while maintaining manufacturing feasibility through standardized process steps.
Solution Approach 2:
Different regions of the semiconductor substrate are doped with different impurity concentrations and types (n-type vs p-type) to create locally optimized electrical characteristics. The photodiode region has high purity for sensitivity, the transfer transistor region has optimized doping for charge transfer efficiency, and the floating diffusion region has specific doping for signal amplification, thereby improving operating speed without requiring complete redesign of the entire device.
2Reliability
If higher impurity concentration is used to improve electrical characteristics, then conductivity increases, but leakage current increases
Solution Approach 1:
The patent implements spatially varying impurity concentrations: the photodiode region uses low impurity concentration to minimize dark current and leakage, while the floating diffusion region uses higher impurity concentration to enhance signal readout capability. The transfer transistor channel region uses precisely controlled doping to ensure adequate conductivity for charge transfer while preventing excessive leakage. This local optimization resolves the contradiction between conductivity and leakage current.
Solution Approach 2:
The transfer transistor acts as an intermediary component that efficiently transfers charges from the photodiode to the floating diffusion region. By optimizing the transfer transistor's channel doping and geometry, charges are rapidly transferred before leakage can occur, effectively mediating between the low-leakage photodiode and the high-conductivity floating diffusion region.
3Reliability
If photodiode and transfer transistor performance is improved, then image sensor performance increases, but manufacturing complexity increases
Solution Approach 1:
The patent combines multiple device structures into a unified pixel architecture where the photodiode, transfer transistor, and floating diffusion region are integrated in a compact arrangement. This merging allows shared process steps for doping, oxidation, and metallization, improving image sensor performance while avoiding the need for separate fabrication lines for each component, thereby maintaining ease of manufacture.
Solution Approach 2:
The invention optimizes critical parameters such as impurity concentration gradients, oxide layer thicknesses, and metallization patterns to achieve high-performance image sensors. By carefully controlling these parameters within standard process capabilities, the patent improves sensor reliability without requiring exotic manufacturing techniques, thus maintaining ease of manufacture through parameter optimization rather than process complexity.
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 approach improves the operating speed and reduces image distortion by providing uniform electrical characteristics across pixels, leading to enhanced image sensor performance.
Implementation Method 1
performing an annealing process to form a floating diffusion region and a channel region surrounding the floating diffusion region by diffusing the n-type impurities and the p-type impurities within the first impurity injection region
Implementation Method 2
performing an annealing process to form a floating diffusion region and a channel region surrounding the floating diffusion region by diffusing the n-type impurities and the p-type impurities within the first impurity injection region
Data Source
AI summary
A method for fabricating an image sensor in accordance with an embodiment of the inventive concepts may include forming first and second photodiodes within a substrate, forming first and second gate electrodes over the substrate, the first gate electrode vertically partially overlapping the first photodiode and the second gate electrode vertically partially overlapping the second photodiode, forming an impurity injection region comprising first and second type impurities between the first and the second gate electrodes, and performing an annealing process to form a floating diffusion region comprising the first type impurities and a channel region comprising the second type impurities. The channel region surrounds lateral surfaces and a bottom surface of the floating diffusion region.