Band-pass filter for stacked sensor cross-talk reduction
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Solution Overview
Problem
In stacked CMOS image sensors, cross-talk between adjacent image sensor elements increases with thickness, degrading image quality due to light penetration and spectral sensitivity overlap, as thicker substrates are needed to separate different wavelengths effectively.
Innovation Solution
Incorporating an inter-substrate band-pass filter between stacked image sensor elements, which reflects specific wavelengths back to the first image sensor, allowing for a thinner substrate and reduced cross-talk while maintaining absorption efficiency by increasing the path length of electromagnetic radiation within the first substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the substrate thickness is increased to separate different wavelengths effectively, then the spectral separation is improved, but the cross-talk between adjacent image sensor elements increases
Solution Approach 1:
The patent divides the light path management into two independent functions: (1) wavelength separation handled by the band-pass filter between substrates, and (2) lateral light confinement handled by the tapered sidewalls within each substrate. This segmentation allows each feature to be optimized independently without compromising the other.
Solution Approach 2:
The tapered sidewalls create a local geometric modification at the edges of the substrate, where the angle gradually changes from vertical to slanted. This local quality change confines light laterally at the boundaries while maintaining optimal thickness for spectral separation in the central region.
2Reliability
If the substrate thickness is increased to improve light absorption, then the absorption efficiency is improved, but the device size increases
Solution Approach 1:
The tapered sidewalls create an optical vibration effect by causing light to bounce at angles as it travels through the substrate. This increases the effective path length of light absorption without increasing the physical thickness of the substrate, similar to how vibration can enhance mixing without increasing container size.
Solution Approach 2:
Instead of increasing absorption efficiency solely in the vertical dimension (thickness), the patent introduces a lateral dimension component through the tapered sidewalls. The angled surfaces extend the light path diagonally, effectively utilizing three-dimensional space to achieve longer optical paths without increasing substrate thickness.
3Object-affected harmful factors
If the substrate thickness is reduced to decrease cross-talk, then the cross-talk is reduced, but the light absorption efficiency decreases
Solution Approach 1:
The tapered sidewalls create multiple internal reflections that effectively 'stir' the light path, increasing the probability of photon-absorber interactions even in thinner substrates. This vibration-like bouncing behavior compensates for the reduced thickness by increasing the number of absorption opportunities.
Solution Approach 2:
The continuous tapered angle ensures that light remains confined and continuously interacts with the absorber material throughout its path. This continuous useful action maintains high absorption efficiency even when the overall substrate thickness is reduced, as light doesn't escape laterally but instead follows the tapered path to multiple interaction points.
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 reduces cross-talk between adjacent image sensor elements, improving quantum efficiency and image quality by allowing for thinner substrates without compromising light absorption, thus enhancing the separation of different wavelengths.
Implementation Method 1
the band-pass filter configured to pass electromagnetic radiation within a passband including the second range of wavelengths and to reflect electromagnetic radiation including the first range of wavelengths
Implementation Method 2
a first image sensor element within a first substrate and configured to generate electrical signals from electromagnetic radiation within a first range of wavelengths
Data Source
AI summary
In some embodiments, the present disclosure relates to an integrated chip structure. The integrated chip structure includes a first image sensor disposed within a first substrate and a second image sensor disposed within a second substrate. The second substrate has a first side facing the first substrate. The first side includes angled surfaces defining one or more recesses within the first side. A band-pass filter is arranged between the first substrate and the second substrate and is configured to reflect electromagnetic radiation that is within a first range of wavelengths.