CMOS Image Sensor Scattering Structure for Pixel Crosstalk
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Solution Overview
Problem
Crosstalk between pixels in CMOS image sensors is high due to photons produced by hot-carrier luminescence passing through the deep trench isolation structure at angles less than the critical angle for total internal reflection, leading to reduced quantum efficiency and performance.
Innovation Solution
Incorporating a scattering structure defined by a first inner trench isolation structure with angled outer sidewalls that refract photons to increase their angle, causing them to be reflected back towards the photodetector by an outer trench isolation structure, thereby reducing crosstalk and improving performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a deep trench isolation structure is used to isolate pixels, then pixel isolation is improved, but photons produced by hot-carrier luminescence pass through at angles less than the critical angle for total internal reflection, causing high crosstalk and reduced quantum efficiency
Solution Approach 1:
The trench isolation structure incorporates angled sidewalls (e.g., 45-degree angles) instead of vertical sidewalls. This curvature/angulation changes the path of photons produced by hot-carrier luminescence, increasing their angle of incidence on the trench walls to exceed the critical angle for total internal reflection, thereby reflecting photons back into the pixel and reducing crosstalk while maintaining quantum efficiency
Solution Approach 2:
The invention changes the geometric parameters of the trench isolation structure by introducing angled sidewalls with specific angles (e.g., 45 degrees). This parameter change modifies the optical path of photons, ensuring that photons generated by hot-carrier luminescence strike the trench walls at angles greater than the critical angle, enabling total internal reflection and preventing crosstalk between adjacent pixels
2Device complexity
If photons are allowed to pass through the trench isolation structure, then device simplicity is maintained, but crosstalk increases and quantum efficiency decreases
Solution Approach 1:
By incorporating angled sidewalls into the existing trench isolation structure, the invention modifies the geometric configuration to achieve total internal reflection of photons. This approach maintains the overall simplicity of the device architecture while significantly improving quantum efficiency by preventing photon leakage and crosstalk between adjacent pixels
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 scattering structure effectively reduces crosstalk by reflecting photons back into the pixel, increasing their absorption and enhancing the image sensor's performance by maintaining photons within the substrate for longer, thus improving quantum efficiency and overall performance.
Implementation Method 1
a scattering structure that is defined by the first inner trench isolation structure and configured to increase an angle at which photons impinge on the outer trench isolation structure
Implementation Method 2
photons produced by hot-carrier luminescence passing through the deep trench isolation structure at angles less than the critical angle for total internal reflection
Data Source
AI summary
The present disclosure relates to an integrated chip including a substrate and a pixel. The pixel includes a photodetector. The photodetector is in the substrate. The integrated chip further includes a first inner trench isolation structure and an outer trench isolation structure that extend into the substrate. The first inner trench isolation structure laterally surrounds the photodetector in a first closed loop. The outer trench isolation structure laterally surrounds the first inner trench isolation structure along a boundary of the pixel in a second closed loop and is laterally separated from the first inner trench isolation structure. Further, the integrated chip includes a scattering structure that is defined, at least in part, by the first inner trench isolation structure and that is configured to increase an angle at which radiation impinges on the outer trench isolation structure.