Solid-State Imaging Device Dark Current Reduction
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Solution Overview
Problem
Existing solid-state imaging devices face challenges in reducing dark current due to carrier outflow from the source/drain region to the light receiving sections, which degrades image quality, despite previous techniques that have only partially addressed this issue.
Innovation Solution
Incorporating a second impurity layer with a higher impurity concentration than the first impurity layer between the photoelectric conversion section and the amplifying section, forming a barrier to suppress carrier outflow and further reduce dark current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a P-type well is used to form source/drain regions and light receiving sections, then device fabrication is simplified, but carriers flow out from peripheral parts to light receiving sections increasing dark current
Solution Approach 1:
The P-type well region is segmented into two distinct impurity concentration zones: a first P-type well with lower impurity concentration for forming light receiving sections, and a second P-type well with higher impurity concentration for forming source/drain regions. This segmentation allows each zone to perform its specific function while minimizing carrier outflow to light receiving sections.
Solution Approach 2:
Different impurity concentrations are applied to different spatial locations within the P-type well structure. The region underlying light receiving sections maintains lower impurity concentration to reduce dark current, while the region for source/drain formation has higher impurity concentration to facilitate carrier generation and reduce noise.
2Object-generated harmful factors
If a P+ guard layer is provided between N+ regions, then dark current is reduced, but device complexity increases
Solution Approach 1:
The guard layer function is merged with the P-type well structure by creating a second P-type well region with higher impurity concentration that serves both as the well for source/drain formation and as the guard layer preventing carrier outflow to light receiving sections, eliminating the need for a separate P+ guard layer.
Solution Approach 2:
The second P-type well with higher impurity concentration performs multiple functions: it forms the source/drain regions, acts as a guard layer to prevent carrier diffusion to adjacent pixels, and reduces dark current in light receiving sections, consolidating multiple protective functions into a single structural element.
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 solution effectively reduces dark current by creating a barrier that prevents carriers from flowing from the source/drain region to the photoelectric conversion section, thereby enhancing image quality.
Implementation Method 1
the photoelectric conversion section converts incident light into a signal charge
Implementation Method 2
The second impurity layer is disposed in a region between the photoelectric conversion section and the amplifying section, has a carrier polarity of the second conductivity type, and has a second impurity concentration higher than the first impurity concentration
Data Source
AI summary
A solid-state imaging device includes a substrate, a photoelectric conversion section, a first impurity layer having a carrier polarity of a second conductivity type, a charge-to-voltage converting section, an amplifying section, and a second impurity layer having a carrier polarity of the second conductivity type. The second impurity layer is disposed in a region between the photoelectric conversion section and the amplifying section. The second impurity concentration of the second P-type impurity layer is made higher than the first impurity concentration of the first impurity layer.