Stacked Image Sensor Structure With Inter-Substrate Band-Pass Filtering
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Solution Overview
Problem
In stacked CMOS image sensors, increased thickness to separate different wavelengths of light leads to spectral cross-talk between adjacent image sensor elements, degrading image quality due to light being sensed by unintended pixels.
Innovation Solution
Incorporating an inter-substrate band-pass filter between stacked image sensor elements, which reflects specific wavelengths of light back to the first image sensor element, allowing for a thinner substrate without reducing radiation absorption, thereby reducing cross-talk and improving quantum efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If substrate thickness is increased to separate different wavelengths of light, then spectral cross-talk between adjacent image sensor elements is reduced, but quantum efficiency deteriorates due to reduced radiation absorption
Solution Approach 1:
The patent introduces a vertical dimension solution by placing a band-pass filter between stacked image sensor elements. This filter selectively transmits specific wavelengths while reflecting others, enabling spectral separation in the vertical stacking direction without requiring increased lateral substrate thickness. This resolves the contradiction by achieving wavelength separation through vertical filtering rather than lateral thickening.
Solution Approach 2:
The band-pass filter acts as an intermediary component between the first and second image sensor elements. It mediates the interaction between incident light and the sensor elements by selectively transmitting desired wavelengths to each sensor while blocking unwanted wavelengths, thereby reducing spectral cross-talk without compromising the radiation absorption efficiency of either sensor element.
2Object-affected harmful factors
If substrate thickness is increased to reduce cross-talk, then image quality improves, but device complexity increases
Solution Approach 1:
Instead of increasing substrate thickness in the lateral dimension to reduce cross-talk, the patent employs a vertical stacking approach with band-pass filters positioned between sensor elements. This dimensional shift allows cross-talk reduction through spectral filtering in the vertical direction, maintaining thin lateral substrate profiles and simplifying overall device structure.
Solution Approach 2:
The patent changes the optical parameters of the system by introducing band-pass filters with specific wavelength transmission characteristics. These filters modify the spectral composition of light reaching each sensor element, enabling cross-talk reduction through parameter-based spectral control rather than structural thickening, thereby maintaining device simplicity.
3Manufacturing precision
If band-pass filter is added between stacked image sensor elements, then spectral separation is improved, but device complexity increases
Solution Approach 1:
The patent segments the optical path by introducing band-pass filters between stacked image sensor elements. Each filter is positioned at a specific vertical location to handle specific wavelength ranges, dividing the complex spectral separation task into manageable segments. This segmentation approach improves spectral separation precision while keeping each individual filter component relatively simple.
Solution Approach 2:
The band-pass filters serve multiple functions simultaneously: they transmit desired wavelengths to specific sensor elements, block unwanted wavelengths to prevent cross-talk, and enable compact vertical stacking of multiple sensors. This multi-functionality achieves high spectral separation precision without proportionally increasing device complexity, as a single filter layer performs multiple optical tasks.
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 band-pass filter effectively separates light spectra vertically while maintaining absorption efficiency, reducing cross-talk between adjacent image sensor elements and enhancing image quality by ensuring light is captured by the intended pixel.
Implementation Method 1
the band-pass filter is configured to pass electromagnetic radiation within a passband including the second range of wavelengths and to reflect electromagnetic radiation outside of the passband
Implementation Method 2
Incorporating an inter-substrate band-pass filter between stacked image sensor elements, which reflects specific wavelengths of light back to the first image sensor element
Implementation Method 3
a first image sensor element within a first substrate and configured to generate electrical signals from electromagnetic radiation within a first range of wavelengths
Implementation Method 4
generate electrical signals from electromagnetic radiation
Data Source
AI summary
In some embodiments, the present disclosure relates to an integrated chip structure. The integrated chip structure includes at least one device on a front side of a semiconductor substrate. A plurality of grating layers are under the at least one device. The plurality of grating layers include at least a first material having a first refractive index alternating with a second material having a second refractive index. Contacts extend through an interlevel dielectric material, and further extend through the semiconductor substrate, to directly contact at least one of the first material and the second material below the at least one device and below the semiconductor substrate underlying the interlevel dielectric material.