Deep Trench Isolation for Image Sensor Pixel 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 is exacerbated by dark current, and existing solutions often fail to entirely eliminate these issues.
Innovation Solution
The use of deep trench isolation structures comprising narrow bandgap semiconductor material, high-k dielectric, and filler material around photodiodes to prevent charge spilling between pixels, inducing positive charge accumulation and reducing electrical interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional isolation techniques are used to reduce pixel crosstalk, then electrical signal leakage between pixels is reduced, but dark current effects are exacerbated
Solution Approach 1:
The isolation structure is segmented into multiple functional layers: a first dielectric material layer providing initial isolation, a doped semiconductor layer creating depletion regions, and a second dielectric material layer providing additional isolation. This multi-layer segmentation allows each layer to address specific aspects of crosstalk and dark current separately, achieving reduction of both harmful effects simultaneously
Solution Approach 2:
The doped semiconductor layer acts as an intermediary structure between adjacent photodiodes. By doping this intermediate layer with dopants having the same polarity as the photodiode junctions, depletion regions are created that extend into the intermediate layer, effectively blocking charge carrier diffusion while maintaining electrical isolation without exacerbating dark current
2Measurement precision
If pixel density is increased to achieve higher resolution, then image sensor resolution is improved, but pixel crosstalk increases due to reduced spacing between pixels
Solution Approach 1:
The isolation approach extends from two-dimensional planar isolation to three-dimensional deep trench isolation. By etching trenches that penetrate through the substrate and filling them with doped semiconductor material, the isolation structure reaches into the vertical dimension, creating depletion regions that effectively block crosstalk even when horizontal spacing between pixels is reduced for higher density arrangements
Solution Approach 2:
The doped semiconductor material is selectively placed in localized regions between adjacent photodiodes. The doping concentration and polarity are specifically tailored for each isolation region to create optimal depletion regions. This localized customization of material properties ensures effective crosstalk blocking at each pixel boundary while maintaining high pixel density
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 mitigates pixel crosstalk and dark current, enhancing image sensor performance by blocking charge transport between pixels and improving image quality.
Implementation Method 1
the high-k dielectric is coupled to the narrow bandgap semiconductor material to induce positive charge accumulation at an interface between the narrow bandgap semiconductor material and the semiconductor material
Implementation Method 2
inducing positive charge accumulation and reducing electrical interference
Data Source
AI summary
An image sensor pixel includes a photodiode disposed in a semiconductor material, and doped regions surrounding the photodiode, at least in part. The doped regions include a doped portion of the semiconductor material. Deep trench isolation structures are disposed in the doped regions, and surround the photodiode at least in part. The deep trench isolation structures include a SiGe layer disposed on side walls of the deep trench isolation structures, a high-k dielectric disposed on the SiGe layer, and a filler material.