Image Sensor Trench Scattering Structure for Quantum Efficiency
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Solution Overview
Problem
CMOS image sensors with avalanche photodiodes (APD) and single-photon avalanche diodes (SPAD) suffer from high crosstalk and low quantum efficiency due to photons produced by hot-carrier luminescence passing through the deep trench isolation (DTI) structure without being reflected back to the photodetector.
Innovation Solution
Incorporating a scattering structure defined by the first inner trench isolation structure, which increases the angle at which photons impinge on the outer trench isolation structure, thereby reflecting photons back towards the photodetector and reducing crosstalk.
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 without being reflected back, causing high crosstalk and low quantum efficiency
Solution Approach 1:
The patent segments the single DTI structure into multiple trench isolation structures at different lateral distances from the photodetector. The first DTI structure is positioned closer to the photodetector while the second DTI structure is positioned farther away. This segmentation allows the first DTI to provide strong isolation and the second DTI to provide additional reflection paths, thereby reducing crosstalk while improving quantum efficiency through multi-level photon management.
Solution Approach 2:
The patent extends the isolation approach from a single lateral distance to multiple lateral distances, adding a spatial dimension to the trench isolation architecture. By positioning DTI structures at different radial distances from the photodetector center, the system creates multiple zones for photon interaction, enabling both crosstalk suppression and enhanced light trapping for improved quantum efficiency.
2Shape
If a deep trench isolation structure is used, then pixel boundary definition is improved, but photons escape into neighboring pixels, reducing quantum efficiency
Solution Approach 1:
The patent divides the pixel boundary definition into multiple concentric zones using first and second DTI structures at different lateral distances. This segmentation creates intermediate isolation zones that progressively manage photon paths, allowing sharp boundary definition while providing multiple opportunities for photon reflection back to the photodetector, thus maintaining both boundary clarity and quantum efficiency.
Solution Approach 2:
The second DTI structure acts as an intermediary element between the first DTI structure and the pixel periphery. It provides an additional layer of photon management that mediates between the need for sharp boundaries and the need to retain photons, offering alternative reflection paths for photons that would otherwise escape, thereby preserving quantum efficiency while maintaining boundary definition.
3Device complexity
If photons are allowed to pass through the DTI structure, then device simplicity is maintained, but crosstalk increases and quantum efficiency decreases
Solution Approach 1:
The patent segments the photon management function across multiple DTI structures positioned at different lateral distances. This segmentation distributes the isolation and reflection functions across several simpler components rather than requiring a single complex structure, achieving improved quantum efficiency through a modular approach that maintains relative device simplicity.
Solution Approach 2:
The patent changes the spatial parameter of the DTI structures by positioning them at different lateral distances from the photodetector. This parameter change transforms the photon interaction characteristics, creating zones with different optical properties that collectively improve quantum efficiency while maintaining a relatively simple trench isolation implementation approach.
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 between pixels and improves the quantum efficiency and overall performance of the image sensor by ensuring that photons are absorbed by the substrate rather than escaping into neighboring pixels.
Implementation Method 1
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, and the outer trench isolation structure laterally surrounds the first inner trench isolation structure along a boundary of the pixel in a second closed loop. The first inner trench isolation structure is laterally separated from the outer trench isolation structure and has a plurality of outer sidewalls defining a scattering structure that is configured to increase an angle at which photons impinge on the outer trench isolation structure.
Implementation Method 2
reflecting photons back towards the photodetector and reducing crosstalk
Implementation Method 3
Some CMOS image sensors are based on avalanche photodiodes (APD) and single-photon avalanche photodiodes (SPAD)
Implementation Method 4
CMOS image sensors with avalanche photodiodes (APD) and single-photon avalanche diodes (SPAD)
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.