Back Side Illumination Image Sensor Embedded IR Filter
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Solution Overview
Problem
Conventional front side illumination (FSI) image sensors have reduced light reception efficiency due to lines on photodiodes, and there is a need for improved performance in various devices such as camcorders, smartphones, and digital cameras, which is addressed by developing back side illumination (BSI) image sensors with an embedded infrared (IR) cut-off filter to enhance manufacturing efficiency, reduce thickness, and lower costs.
Innovation Solution
A BSI image sensor design incorporating a substrate with photodiodes, a dark current suppression layer, an IR cut-off filter formed by alternately stacking low and high refractive index films, a light shield pattern with openings, and a planarization layer, along with a lens to improve light collection and reduce dark current, while embedding the IR cut-off filter within the image sensor to enhance manufacturing efficiency and reduce thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If an IR cut-off filter is embedded within the image sensor, then manufacturing efficiency is improved and thickness is reduced, but device complexity increases due to additional layers and structures
Solution Approach 1:
The patent merges the IR cut-off filter with the image sensor by forming the filter layers (first and second refractive index layers) directly on the substrate during the sensor manufacturing process. This integration eliminates the need for separate filter components and assembly steps, thereby improving manufacturing efficiency while the systematic layer integration manages the complexity through standardized fabrication procedures
Solution Approach 2:
The substrate serves multiple functions: it acts as both the base for the photodiodes and the foundation for the IR cut-off filter structure. The first refractive index layer simultaneously serves as part of the filter structure and as an optical interface layer, reducing the need for additional separate components and simplifying the overall device architecture
2Length of moving object
If an IR cut-off filter is embedded within the image sensor, then thickness is reduced, but device complexity increases due to additional layers and structures
Solution Approach 1:
The IR cut-off filter structure is nested within the image sensor architecture by placing the first refractive index layer on the substrate and the second refractive index layer on the first layer, creating a compact nested configuration. This nesting approach minimizes the overall thickness while organizing multiple functional layers in a space-efficient manner that manages structural complexity
Solution Approach 2:
The patent utilizes the vertical dimension (z-axis) to stack functional layers (substrate, photodiodes, first refractive index layer, second refractive index layer) rather than spreading them out horizontally. This vertical stacking reduces the horizontal footprint and overall thickness while organizing complexity in the vertical dimension through systematic layering
3Reliability
If a light shield pattern with openings is added to block IR radiation, then image quality is improved, but light collection efficiency is reduced
Solution Approach 1:
The light shield pattern is designed with local openings (through-holes) at specific positions where light collection is needed, while maintaining shielding in other areas. This creates local quality variations in the light shield layer, allowing it to simultaneously block IR radiation in most areas while permitting visible light transmission at designated openings to maintain light collection efficiency
Solution Approach 2:
The light shield pattern functions as a composite structure combining light-blocking material with transparent or semi-transparent openings. This composite design allows the same structure to perform dual functions: blocking harmful IR radiation while allowing useful visible light to pass through the openings to reach the photodiodes, thus balancing image quality and light collection efficiency
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 BSI image sensor with an embedded IR cut-off filter improves light collection efficiency, reduces dark current, and enhances manufacturing efficiency, leading to a thinner and cost-effective image sensor module suitable for various electronic devices, including smartphones, by effectively blocking IR radiation and improving image quality.
Implementation Method 1
an infrared radiation (IR) cut-off filter above the photodiode
Implementation Method 2
a dark current suppression layer above the photodiode and including a stack of a plurality of layers that each have a negative charge
Implementation Method 3
a lens on the planarization layer
Implementation Method 4
a plurality of pixels configured to generate electrical signals responsive to light incident on the back side of the substrate. Each of the plurality of pixels may include a photodiode
Data Source
AI summary
Back side illumination (BSI) image sensors are provided. A BSI image sensor includes a substrate and a plurality of pixels configured to generate electrical signals responsive to light incident on the substrate. Each of the plurality of pixels includes a photodiode, an infrared radiation (IR) cut-off filter above the photodiode, a light shield pattern above the photodiode and including an opening corresponding to an area of 1 to 15% of each of the plurality of pixels, a planarization layer on the light shield pattern, and a lens on the planarization layer.