Back-Side Illuminated CMOS Image Sensor Cross-Talk Reduction
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Solution Overview
Problem
Complementary metal oxide semiconductor image sensors face operational issues due to light interference from metal and dielectric layers in front-side illumination configurations and cross-talk between adjacent pixel regions in back-side illumination configurations, affecting precision and efficiency.
Innovation Solution
A back-side illuminated CMOS image sensor design incorporating a reflective grid and a gap between color filters to ensure light is directed accurately to photosensitive diodes, reducing cross-talk and enhancing efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If front-side illumination configuration is used, then light can be directed to photodiodes through transfer transistors, but metal layers and dielectric layers block light and cause processing issues
Solution Approach 1:
The patent inverts the traditional front-side illumination configuration by implementing back-side illumination. Light enters through the back of the substrate, passing through the photosensitive diode before reaching the transfer transistor and metal layers on the front side. This inversion eliminates the problem of light being blocked by metal and dielectric layers while maintaining the ability to control light direction through the transfer transistor.
2Object-affected harmful factors
If back-side illumination configuration is used, then light reaches photodiodes before transfer transistors and metal layers, but adjacent pixel regions interfere with each other causing cross-talk
Solution Approach 1:
The patent divides the substrate into isolated pixel regions separated by isolation structures. These isolation regions physically segment the pixel areas, preventing light from adjacent pixels from reaching non-corresponding photosensitive diodes. This segmentation eliminates cross-talk between adjacent pixel regions while maintaining the back-side illumination configuration.
3Area of stationary object
If pixel regions are placed adjacent to each other for compact design, then device area is reduced, but cross-talk between adjacent pixels reduces precision and efficiency
Solution Approach 1:
The patent implements isolation regions that physically separate adjacent pixel regions. These isolation structures create distinct boundaries between pixels, allowing compact arrangement while preventing optical interference. The segmentation ensures that light from one pixel cannot reach adjacent pixels, eliminating cross-talk even in densely packed configurations.
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 solution effectively minimizes light interference and cross-talk, improving the precision and efficiency of image capture by ensuring light reaches the correct photosensitive diodes, thereby enhancing the overall performance of the image sensor.
Implementation Method 1
A back-side illuminated CMOS image sensor design incorporating a reflective grid and a gap between color filters to ensure light is directed accurately to photosensitive diodes
Implementation Method 2
Complementary metal oxide semiconductor image sensors generally utilize a series of photodiodes formed within an array of pixel regions of a semiconductor substrate in order to sense when light has impacted the photodiode
Data Source
AI summary
A system and method for reducing cross-talk between photosensitive diodes is provided. In an embodiment a first color filter is formed over a first photosensitive diode and a second color filter is formed over a second photosensitive diode, and a gap is formed between the first color filter and the second color filter. The gap will serve to reflect light that otherwise would have crossed from the first color filter to the second color filter, thereby reducing cross-talk between the first photosensitive diode and the second photosensitive diode. A reflective grid may also be formed between the first photosensitive diode and the second photosensitive diode in order to assist in the reflection and further reduce the amount of cross-talk.