Trench Barrier Layer for Image Sensor Noise Reduction
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Solution Overview
Problem
Conventional image sensors, particularly back-side illumination (BSI) image sensors, suffer from noise and signal deterioration due to unwanted photo-charges generated in regions other than the photoelectric conversion region, leading to increased signal-to-noise ratios and degraded image sensor characteristics.
Innovation Solution
The implementation of a barrier layer in the floating diffusion region to prevent unwanted photo-charges by forming a trench with a barrier layer that covers the bottom and side planes, and a conducting layer gap-filled within the trench, which includes insulation layers to absorb or reflect incident light, thereby blocking light from reaching the floating diffusion region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional floating diffusion region is used without additional structures, then the device complexity is low, but unwanted photo-charges are generated causing noise and deteriorated image sensor characteristics
Solution Approach 1:
The floating diffusion region is segmented by introducing a trench that divides it into separate areas. This segmentation prevents unwanted photo-charges generated in certain regions from affecting the entire floating diffusion region, thereby reducing noise while maintaining a relatively simple overall structure.
Solution Approach 2:
Different regions of the floating diffusion structure are given different properties through the trench and barrier layer configuration. The trench creates localized areas with different light exposure characteristics, allowing certain regions to be protected from generating unwanted photo-charges while other regions maintain normal photoelectric conversion function.
2Reliability
If the barrier layer covers only the bottom of the trench, then the manufacturing precision requirement is lower, but light can still reach the floating diffusion region through the side planes causing photo-charge generation
Solution Approach 1:
The barrier layer coverage is extended from a single-dimensional bottom surface to a multi-dimensional structure that includes both the bottom plane and the side planes of the trench. This dimensional extension ensures complete light blocking in all directions while maintaining reasonable manufacturing precision requirements by following the natural trench geometry.
3Reliability
If a simple insulation layer is used as the barrier layer, then the ease of manufacture is high, but the light absorption and reflection effectiveness is insufficient under strong light conditions
Solution Approach 1:
The barrier layer is constructed as a composite structure with multiple insulation layers having different refractive indexes. This composite configuration enhances light absorption and reflection effectiveness through optical interference and multiple internal reflections, providing superior light blocking performance while maintaining manufacturing feasibility through standard semiconductor fabrication processes.
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 the signal-to-noise ratio, preventing noise generation in the floating diffusion region and improving image sensor characteristics by blocking unwanted photo-charges, especially under strong light conditions.
Implementation Method 1
The barrier layer may include an insulation layer, which absorbs or reflects incident light
Implementation Method 2
The barrier layer may include an insulation layer, which absorbs or reflects incident light
Data Source
AI summary
An age sensor including a transfer gate formed on a substrate, a photoelectric conversion region formed on a side of the transfer gate, a floating diffusion region with a trench formed on another side of the transfer gate, a barrier layer which covers a bottom of the trench and a conducting layer, which is gap-filled in the trench.