Partially Encapsulating Attenuation Layer for Image Sensor Crosstalk
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Solution Overview
Problem
Image sensors face challenges in reducing crosstalk between photodiodes, particularly due to light with high incident angles, which affects pixel performance and leads to petal flare, while maintaining high dynamic range and quantum efficiency.
Innovation Solution
Incorporating a partially encapsulating light attenuation layer under a metal grid that extends over small photodiodes, reducing crosstalk without affecting the quantum efficiency of large photodiodes, and using a high-κ oxide layer with negative fixed charges to improve electrical isolation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a light attenuation layer is added to reduce crosstalk between photodiodes, then pixel performance is improved, but device complexity increases
Solution Approach 1:
The light attenuation layer is selectively positioned only in regions where crosstalk occurs between adjacent photodiodes, rather than uniformly across the entire sensor. This localized approach reduces crosstalk while minimizing added complexity to the overall device structure.
Solution Approach 2:
The light attenuation layer is integrated within the existing multi-layer sensor structure, nested between other functional layers such as the color filter layer and photodiode layer. This nesting approach incorporates the attenuation function without significantly increasing device complexity.
2Reliability
If a light attenuation layer is used to suppress petal flare, then image quality is improved, but manufacturing precision requirements increase
Solution Approach 1:
The light attenuation layer utilizes variations in material composition, thickness, and optical properties to achieve effective petal flare suppression. By adjusting these parameters, the layer can be optimized for performance while accommodating standard manufacturing tolerances.
Solution Approach 2:
The light attenuation layer is formed using composite material structures that combine multiple materials with complementary optical properties. This composite approach enhances attenuation effectiveness while providing manufacturing flexibility to meet precision requirements.
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 effectively suppresses petal flare and enhances pixel performance by reducing crosstalk while maintaining high dynamic range and quantum efficiency.
Implementation Method 1
a light attenuation layer that partially encapsulates the first photodiode by extending laterally from the first DTI region to the second DTI region between the semiconductor material and the buffer oxide layer
Implementation Method 2
using a high-κ oxide layer with negative fixed charges to improve electrical isolation
Implementation Method 3
The image sensor includes an array of pixels having photosensitive elements (e.g., photodiodes) that absorb a portion of the incident image light and generate image charge upon absorption of the image light
Data Source
AI summary
A pixel cell includes a first photodiode, a second photodiode, a first deep trench isolation region, a second deep trench isolation region, a buffer oxide layer, and a light attenuation layer. The attenuation layer partially encapsulates the first photodiode by extending laterally from the first deep trench isolation region to the second deep trench isolation region between the semiconductor material and the buffer oxide layer.