Stacked Color and Infrared Image Sensor for High-Fill-Factor Pixels
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Solution Overview
Problem
Designing a color and infrared image sensor that simultaneously achieves high resolution, global shutter capability, small pixel size, and high filling factor is challenging due to the need to balance these constraints in image sensor design.
Innovation Solution
The image sensor incorporates a silicon substrate with MOS transistors, first and second photodiodes, a photosensitive layer, color filters, and an infrared filter, arranged in a configuration that allows for simultaneous integration phases and high filling factor, with sub-pixels optimized for different frequency ranges and readout circuits controlling charge transfer for each photodiode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the pixel size is reduced to increase resolution, then the resolution is improved, but the filling factor deteriorates
Solution Approach 1:
The patent transitions from a planar arrangement to a three-dimensional stacked architecture where color photodiodes and infrared photodiodes are positioned at different depths within the substrate. This vertical stacking enables multiple photodetector types to occupy the same lateral footprint, thereby maintaining high filling factor while achieving high resolution through reduced pixel pitch.
Solution Approach 2:
The patent implements a nested structure where infrared photodiodes are positioned beneath color photodiodes within the same pixel column. The infrared photodiodes are arranged in regions where color photodiodes are absent or reduced, creating a nested configuration that maximizes the use of available space and maintains high filling factor for both detector types simultaneously.
2Adaptability or versatility
If global shutter capability is implemented for simultaneous color and infrared acquisition, then the versatility is improved, but the device complexity deteriorates
Solution Approach 1:
The patent divides the pixel array into distinct regions: color pixel columns and infrared pixel columns. Each region has dedicated readout circuitry and can be controlled independently. This segmentation allows the implementation of global shutter capability for both color and infrared channels without requiring a completely unified complex control system, thereby managing device complexity through modular design.
3Measurement precision
If the pixel size is reduced to increase resolution, then the resolution is improved, but the area of each pixel deteriorates
Solution Approach 1:
The patent exploits the third dimension (depth) by stacking photodiodes vertically within the substrate. This allows the pixel pitch in the lateral plane to be reduced for higher resolution while the vertical stacking maintains sufficient active area for both color and infrared photodetection, effectively decoupling resolution from pixel area constraints.
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 enables the image sensor to achieve resolutions greater than 2,560 ppi, pixel sizes smaller than 10 μm, and filling factors greater than 50%, while maintaining global shutter capability for both color and infrared image acquisition.
Implementation Method 1
first photodiodes formed in the substrate and configured to absorb the electromagnetic waves of the visible spectrum and of a first portion of the infrared spectrum
Implementation Method 2
a photosensitive layer covering the substrate and configured to absorb the electromagnetic waves of the visible spectrum and to give way to the electromagnetic waves of said first portion of the infrared spectrum
Implementation Method 3
an infrared filter, the color filters being interposed between the photosensitive layer and the infrared filter, the infrared filter being configured to give way to the electromagnetic waves of the visible spectrum, to give way to the electromagnetic waves of said first portion of the infrared spectrum, and to block the electromagnetic waves of at least a second portion of the infrared spectrum
Data Source
AI summary
A color and infrared image sensor includes a silicon substrate, MOS transistors formed in the substrate and on the substrate, first photodiodes at least partly formed in the substrate, a photosensitive layer covering the substrate, and color filters, the photosensitive layer being interposed between the substrate and the color filters. The image sensor further includes first and second electrodes on either side of the photosensitive layer and delimiting second photodiodes in the photosensitive layer, the first photodiodes being configured to absorb the electromagnetic waves of the visible spectrum and of a first portion of the infrared spectrum and the photosensitive layer being configured to absorb the electromagnetic waves of the visible spectrum and to give way to the electromagnetic waves of said first portion of the infrared spectrum.