Dummy Vertical Transistor Structure for CMOS Image Sensor Crosstalk Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Cross talk between photodetectors in complementary metal-oxide semiconductor (CMOS) image sensors leads to imbalances in radiation magnitude and phase, increasing noise and decreasing sensitivity and reliability.
Innovation Solution
Incorporating a dummy vertical transistor structure beneath each photodetector, which redirects incident radiation back to the photodetector, thereby reducing cross talk between adjacent photodetectors through deep trench isolation and interconnect structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If photodetectors are arranged closely in an array to increase pixel density, then productivity and sensor resolution are improved, but cross talk between adjacent photodetectors increases causing noise and reducing reliability
Solution Approach 1:
The patent divides the sensor array into isolated photodetector units by introducing dummy vertical transistor structures between adjacent photodetectors. These dummy transistors act as segmentation barriers that physically divide the continuous substrate into discrete functional units, preventing cross-talk while maintaining high pixel density.
Solution Approach 2:
The dummy vertical transistor structures serve as intermediary elements positioned between adjacent photodetectors. These intermediaries absorb or block stray charge carriers and electromagnetic signals that would otherwise cause cross-talk, thereby protecting the reliability of adjacent photodetector signals without reducing pixel density.
2Area of stationary object
If photodetectors are arranged closely to reduce sensor size, then device compactness is improved, but cross talk increases leading to noise and reduced sensitivity
Solution Approach 1:
By introducing dummy vertical transistor structures between closely spaced photodetectors, the patent segments the compact sensor array into isolated functional units. This segmentation maintains the small sensor footprint while preventing cross-talk interference between adjacent photodetectors, thereby preserving signal sensitivity despite the reduced area.
Solution Approach 2:
The dummy vertical transistors act as intermediary protective structures in the compact layout. They are positioned strategically between adjacent photodetectors to block stray signals and charge carriers, enabling close spacing without compromising the sensitivity and reliability of individual photodetector elements.
3Device complexity
If no isolation structures are used between photodetectors, then device complexity is reduced, but cross talk between adjacent photodetectors increases causing noise
Solution Approach 1:
The dummy vertical transistor structures serve as intermediary elements that actively block cross-talk signals between photodetectors. Although they add some structural elements, they are formed using standard CMOS fabrication processes and occupy minimal space, providing effective cross-talk suppression with relatively low added complexity.
Solution Approach 2:
The patent changes the electrical and physical parameters of the substrate regions between photodetectors by introducing doped dummy transistor structures. These structures modify the local electrical characteristics (such as carrier concentration and conductivity) to prevent charge carrier diffusion and signal leakage, thereby reducing cross-talk noise with minimal structural addition.
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
This configuration decreases cross talk, enhances the reliability and accuracy of image sensors by ensuring equal radiation exposure to each photodetector, improving sensitivity.
Implementation Method 1
dummy vertical transistor structure beneath each photodetector, which redirects incident radiation back to the photodetector
Data Source
AI summary
Various embodiments of the present disclosure are directed towards a method for forming an image sensor, the method includes forming a photodetector in a substrate. A first vertical gate electrode is formed extending into a first surface of the substrate. The first vertical gate electrode is adjacent to a first side of the photodetector. A second vertical gate electrode is formed extending into the first surface of the substrate. The second vertical gate electrode is adjacent to a second side of the photodetector opposite the first side.