Image Sensor Pixel Isolation Structure for Leakage Current Reduction
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Solution Overview
Problem
Current image sensors, particularly CMOS image sensors, face challenges in maximizing the light-capturing area while minimizing leakage current due to the design of active regions and isolation layers, which affects the efficiency and footprint of the pixel structure.
Innovation Solution
The image sensor design incorporates a first device isolation layer around each pixel and a second device isolation layer that delimits active regions within the semiconductor substrate, separating the floating diffusion region and the ground region from the transfer transistor gate, and connects the ground region to a ground voltage terminal, optimizing the layout to enhance light capture and reduce leakage current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If the active region is enlarged to increase the light-capturing area, then the photoelectric converter efficiency is improved, but the leakage current increases
Solution Approach 1:
The patent divides the isolation structure into two distinct layers: a first device isolation layer that separates adjacent pixels, and a second device isolation layer that specifically delimits the active region within each pixel. This segmentation allows the active region to be enlarged for better light capture while the second isolation layer contains the leakage current within specific regions, preventing it from affecting the entire pixel structure.
2Reliability
If the pixel structure is optimized to reduce leakage current, then the signal quality is improved, but the light-capturing area is reduced
Solution Approach 1:
The patent applies different isolation characteristics to different regions of the pixel structure. The second device isolation layer is strategically positioned to delimit the active region where leakage current control is critical for signal quality, while the first device isolation layer provides broader pixel separation. This localized approach ensures high signal quality in the active region without unnecessarily reducing the overall light-capturing area of the pixel.
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 design maximizes the light-capturing area for the photoelectric converter while minimizing leakage current, improving the overall performance and efficiency of the image sensor without compromising the pixel footprint.
Implementation Method 1
a photoelectric converter region (27) disposed within the semiconductor substrate as spaced apart from the gate. The photoelectric converter region (27) constitutes a photoelectric converter that converts external light to charges
Data Source
AI summary
An image sensor includes a first device isolation layer separating a plurality of pixels from one another, and a second device isolation layer disposed along inner side surfaces of parts of the first device isolation layer that extend around the pixels. The second device isolation layer delimits an active region of the semiconductor substrate. Each pixel includes a photoelectric converter, a floating diffusion region, a ground region, and a gate of a transfer transistor. The gate extends into the active region of the semiconductor substrate. The ground region is electrically connected to a ground voltage terminal.