Biased Deep Trench Isolation for Image Sensor Crosstalk
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Solution Overview
Problem
Pixel crosstalk in semiconductor image sensors leads to image degradation due to electrical signal leakage between pixels, which existing solutions often exacerbate dark current or fail to fully mitigate.
Innovation Solution
The implementation of biased deep trench isolation structures using conductive and dielectric materials, such as tungsten and hafnium oxide, to electrically and optically isolate photodiodes, reducing charge transport between pixels by inducing a positive charge that blocks surface states and minimizes dark current and white pixel issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If heavily doped regions are used to isolate individual pixels, then pixel crosstalk is reduced, but dark current increases
Solution Approach 1:
The patent divides the isolation function into multiple components: lightly doped regions for optical isolation and heavily doped regions for electrical isolation. This segmentation allows each component to perform its specific function optimally without the heavily doped regions being the sole source of isolation, thereby reducing their negative impact on dark current while maintaining effective pixel separation.
Solution Approach 2:
The patent introduces an intermediate lightly doped region between the photodiode and the heavily doped isolation region. This intermediary layer provides optical isolation and reduces the direct interaction between adjacent pixels, allowing the heavily doped regions to focus on electrical isolation without exacerbating dark current as much.
2Object-affected harmful factors
If heavily doped regions are used to isolate individual pixels, then electrical signal leakage between pixels is reduced, but image sensor sensitivity decreases
Solution Approach 1:
The isolation structure is segmented into lightly doped regions that provide optical isolation and heavily doped regions that provide electrical isolation. This segmentation allows the heavily doped regions to effectively block electrical signal leakage while the lightly doped regions maintain optical separation, preserving overall sensor sensitivity.
Solution Approach 2:
Different doping levels are applied to different regions: lightly doped regions surround each photodiode for optical isolation, while heavily doped regions are positioned at specific locations for electrical isolation. This local differentiation optimizes each region's function, reducing electrical leakage without uniformly degrading sensitivity across the entire sensor.
3Object-affected harmful factors
If post-acquisition algorithms are employed to reduce image noise, then crosstalk effects are mitigated, but processing complexity increases
Solution Approach 1:
The patent implements physical isolation structures (lightly and heavily doped regions) during the manufacturing process to prevent crosstalk before image acquisition occurs. This preliminary physical mitigation reduces or eliminates the need for complex post-acquisition algorithms, thereby reducing processing complexity while still effectively mitigating crosstalk effects.
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 approach effectively reduces pixel crosstalk and dark current, enhancing image sensor sensitivity and resolution while avoiding the adverse effects of previous mitigation methods.
Implementation Method 1
biased deep trench isolation structures using conductive and dielectric materials, such as tungsten and hafnium oxide, to electrically and optically isolate photodiodes, reducing charge transport between pixels by inducing a positive charge that blocks surface states
Data Source
AI summary
An image sensor includes a plurality of photodiodes disposed in a semiconductor material, and a through-semiconductor-via coupled to a negative voltage source. Deep trench isolation structures are disposed between individual photodiodes in the plurality of photodiodes to electrically and optically isolate the individual photodiodes. The deep trench isolation structures include a conductive material coupled to the through-semiconductor-via, and a dielectric material disposed on sidewalls of the deep trench isolation structures between the semiconductor material and the conductive material.