Image Sensor Attenuation Layer Sidewall Design
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Solution Overview
Problem
Image sensors with split pixel structures face issues with high angle incident light and internal reflections that can saturate small photodiodes, affecting their sensitivity and dynamic range.
Innovation Solution
An attenuation layer is deposited on the sidewall of the buffer layer above large photodiodes and surrounding the small photodiodes, preventing high angle incident light and reflections from activating small photodiodes, while maintaining light sensitivity of large photodiodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an attenuation layer is deposited on the sidewall of the buffer layer above large photodiodes, then the sensitivity of small photodiodes to high intensity light is improved, but the light sensitivity of large photodiodes may be reduced
Solution Approach 1:
The attenuation layer is selectively deposited only on the sidewalls of the buffer layer above large photodiodes, creating a localized optical attenuation structure. This local modification allows the attenuation layer to block high-angle incident light and internal reflections from reaching small photodiodes, while the large photodiodes maintain their light sensitivity through their top surfaces and central regions that are not blocked by the sidewall-only attenuation structure.
2Object-generated harmful factors
If the attenuation layer covers the top surface of large photodiodes, then crosstalk to small photodiodes is reduced, but the light collection efficiency of large photodiodes decreases
Solution Approach 1:
The attenuation layer is segmented to cover only the sidewall regions of the buffer layer rather than the entire top surface. This segmentation approach divides the buffer layer surface into attenuated sidewall regions and non-attenuated top surface regions, allowing the attenuation layer to block crosstalk paths while leaving the primary light collection areas of large photodiodes exposed and functional.
3Object-affected harmful factors
If a complete attenuation layer is deposited over all photodiodes, then high angle incident light is blocked, but the overall quantum efficiency of the sensor is reduced
Solution Approach 1:
The attenuation layer is applied locally only to sidewall regions rather than uniformly across all photodiode surfaces. This localized application blocks high-angle incident light and internal reflections that cause crosstalk, while maintaining quantum efficiency by leaving the top surfaces where primary light enters the large photodiodes completely exposed and unattenuated.
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 solution improves the performance of image sensors by reducing crosstalk and saturation of small photodiodes, enhancing their sensitivity to high intensity light and maintaining the sensitivity of large photodiodes.
Implementation Method 1
An attenuation layer is deposited on the sidewall of the buffer layer above large photodiodes and surrounding the small photodiodes, preventing high angle incident light and reflections from activating small photodiodes
Data Source
AI summary
An image sensor includes a substrate having a plurality of small photodiodes and a plurality of large photodiodes surrounding the small photodiodes. The substrate further includes a plurality of deep trench isolation structures in regions of the substrate between ones of the small photodiodes and the large photodiodes. Each of large photodiodes having a full well capacity larger than each of the small photodiodes. The image sensor further includes an array of color filters disposed over the substrate, a first and second buffer layer disposed between the substrate and the array of color filters, metal grid structures disposed between the color filters and above the first buffer layer, and an attenuation layer portion above a region of the substrate between ones of the large and small photodiodes, the attenuation layer portion is between the first and second buffer layers and normal to an upper surface of the substrate.