BSI Image Sensor Pixel Layout for Dark Current and Light Crosstalk
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Solution Overview
Problem
Backside illumination (BSI) image sensors face challenges in reducing dark current and improving light-receiving efficiency due to the arrangement of wiring above the photodiode, which affects the performance of image sensors in devices such as smartphones and digital cameras.
Innovation Solution
The implementation of a BSI image sensor design that includes a photodiode, a dark current suppression layer, a light shield grid with an opening area of 1 to 15% of the pixel area, a planarization layer, a lens, and an anti-reflective film, along with a deep trench isolation (DTI) to reduce interference between pixels and enhance light collection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If wiring is arranged above the photodiode in FSI image sensors, then device complexity is reduced, but light-receiving efficiency deteriorates
Solution Approach 1:
The patent inverts the conventional FSI structure by placing the photodiode on the back side of the substrate, allowing light to enter from the rear. This inversion removes the wiring obstruction from the light path, achieving both high light-receiving efficiency and manageable device complexity through the BSI architecture
2Object-affected harmful factors
If a light shield grid with small opening area is used, then light interference between pixels is reduced, but light-receiving efficiency deteriorates
Solution Approach 1:
The light shield grid is designed with spatially varying properties: the opening area ratio is specifically optimized to be 1-15% in different regions, and the grid line widths are adjusted locally. This allows sufficient light transmission in photodiode regions while providing strong shielding in pixel boundary areas, resolving the contradiction between light interference reduction and light-receiving efficiency
Solution Approach 2:
The patent employs parameter optimization by setting the opening area ratio within a specific range (1-15%) and adjusting grid line widths to achieve the desired balance. By changing these geometric parameters, the design achieves both effective pixel isolation and adequate light transmission
3Reliability
If multiple layers are added to suppress dark current and shield light, then image sensor performance is improved, but device complexity increases
Solution Approach 1:
The patent combines multiple functional layers into an integrated BSI structure: the deep trench isolation structure serves both mechanical isolation and electrical isolation functions, the light shield grid provides both optical shielding and structural support, and the planarization layer simultaneously flattens the surface and provides additional isolation. This merging approach achieves high performance while controlling device complexity through multi-functional integration
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 effectively suppresses dark current and improves light-receiving efficiency, leading to enhanced image sensor performance by preventing light interference and promoting accurate light positioning on the photodiode, thereby improving the quality of images captured.
Implementation Method 1
a pixel configured to generate electrical signals in response to incident light. The pixel comprises a photodiode
Implementation Method 2
an anti-reflective film between the photodiode and the lens
Data Source
AI summary
In some example embodiments, a back side illumination (BSI) image sensor may include a pixel configured to generate electrical signals in response to light incident on a back side of a substrate. In some example embodiments, the pixel includes, a photodiode, a device isolation film adjacent to the photodiode, a dark current suppression layer above the photodiode, a light shield grid above the photodiode and including an opening area of 1 to 15% of an area of the pixel, a light shielding filter layer above the light shield grid, a planarization layer above the light shielding filter layer, a lens above the planarization layer, and/or an anti-reflective film between the photodiode and the lens.