Stacked Imaging Device Dark Current Reduction via Intermediate Layer
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Solution Overview
Problem
Stacked imaging devices face challenges in reducing leakage current from the charge storage region, known as dark current, which degrades image quality due to minority carriers generated in the semiconductor substrate flowing into the charge storage region.
Innovation Solution
The imaging device incorporates a semiconductor substrate with a specific layer structure, including a first layer with one conductivity type and a second layer with a different conductivity type closer to the surface, featuring a pixel with a photoelectric converter and diffusion regions. The configuration optimizes the distance and potential distribution to absorb minority carriers, reducing their inflow into the charge storage region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a stacked imaging device structure is used with a charge storage region, then photoelectric conversion efficiency is improved, but leakage current (dark current) increases due to minority carriers flowing into the charge storage region
Solution Approach 1:
An intermediate layer with a third conductivity type different from both the first and second conductivity types is introduced between the second layer and the charge storage region. This intermediate layer acts as a mediator that prevents minority carriers from flowing into the charge storage region while maintaining the photoelectric conversion function of the stacked structure.
Solution Approach 2:
The patent applies local quality by creating a specific region with a third conductivity type at a particular location (between the second layer and charge storage region) rather than uniformly changing the entire structure. This localized modification targets the specific problem of minority carrier flow without affecting the overall photoelectric conversion efficiency.
2Productivity
If the charge storage region is positioned closer to the photoelectric converter, then charge collection efficiency is improved, but dark current increases due to thermal generation of minority carriers
Solution Approach 1:
The intermediate layer with third conductivity type serves as a barrier that prevents thermally generated minority carriers in the charge storage region from flowing into the photoelectric converter, thereby reducing dark current while allowing efficient charge collection when photons are present.
Solution Approach 2:
The patent changes the conductivity type parameter of the intermediate layer to create a potential barrier that selectively blocks minority carriers. This parameter change (introducing a third conductivity type) modifies the electrical properties at the interface between the charge storage region and the second layer, reducing dark current without compromising charge collection efficiency.
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 design effectively minimizes leakage current and its variation in the charge storage region, leading to improved image quality by reducing dark current and enhancing the accuracy of image capture.
Implementation Method 1
a photoelectric converter configured to convert light into charge
Data Source
AI summary
An imaging device including a semiconductor substrate having a first surface, the semiconductor substrate including: a first layer containing an impurity of a first conductivity type; a second layer containing an impurity of a second conductivity type different from the first conductivity type, the second layer being closer to the first surface than the first layer is; and a pixel. The pixel includes a photoelectric converter configured to convert light into charge; and a first diffusion region containing an impurity of the first conductivity type, the first diffusion region facing the first layer via the second layer, configured to store at least a part of the charge. The first layer having a second surface adjacent to the second layer, the second surface including a convex portion toward the first surface, and the convex portion facing the first diffusion region.