BSI Image Sensor Pixel Layout for Dark Current Suppression
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Solution Overview
Problem
Front side illumination (FSI) image sensors face a decrease in light-receiving efficiency due to wiring arrangements above the photodiode, while back side illumination (BSI) image sensors aim to improve this efficiency by placing wiring below the photodiode.
Innovation Solution
A back side illumination image sensor is designed with a pixel configuration that includes a photodiode, a device isolation film, a dark current suppression layer, a light shield grid with a specific opening area, a light shielding filter layer, a planarization layer, a lens, and an anti-reflective film to enhance light reception and reduce dark current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If wiring is arranged above the photodiode (FSI structure), then device complexity is reduced and manufacturing is easier, but light-receiving efficiency decreases
Solution Approach 1:
The patent inverts the conventional FSI structure by placing the photodiode above the wiring instead of below it. This BSI (back-side illumination) configuration allows light to incident on the photodiode from the top without being blocked by wiring, thereby improving light-receiving efficiency while maintaining manufacturing feasibility through adapted fabrication processes
2Use of energy by moving object
If wiring is arranged below the photodiode (BSI structure), then light-receiving efficiency improves, but device complexity increases
Solution Approach 1:
The patent segments the device into distinct functional layers: photodiode layer, wiring layer, lens layer, and color filter layer, arranged in a stacked configuration. This segmentation allows each component to be optimized independently and simplifies the overall design by separating optical functions from electrical functions, thereby reducing the complexity increase associated with BSI structure
3Reliability
If light shield grid with small opening area is used, then dark current suppression improves, but light reception efficiency may decrease
Solution Approach 1:
The light shield grid is designed with non-uniform opening distribution, concentrating the opening area (1-15% of pixel area) at the central portion of the photodiode where light reception is most critical. This local quality approach suppresses dark current in peripheral regions while maintaining high light reception efficiency at the center, resolving the contradiction between dark current suppression and light reception
4Manufacturing precision
If multiple layers (light shield grid, color filter, lens) are added, then light distribution control improves, but device complexity increases
Solution Approach 1:
The patent merges multiple light control functions into a single integrated color filter layer that combines wavelength filtering, light shielding, and structural support functions. The lens is integrated directly above the photodiode array, and the light shield grid is combined with the pixel structure, thereby achieving precise light distribution control while minimizing the increase in device complexity through 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
The proposed solution improves light-receiving efficiency and reduces dark current, leading to enhanced performance of the image sensor by effectively managing light distribution and suppressing unwanted current.
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
Implementation Method 3
a lens above the planarization layer
Implementation Method 4
a light shielding filter layer above the light shield grid
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.