Photoelectric Conversion Pixel Isolation Layout for Noise Suppression
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Solution Overview
Problem
The performance of photoelectric conversion apparatuses, such as CMOS image sensors, is not consistently improved by trench layouts due to varying positions of trenches, which can lead to reduced sensitivity or increased noise.
Innovation Solution
A photoelectric conversion apparatus with a semiconductor layer featuring a first and second surface, including element and pixel isolating portions constituted by grooves that pass through a virtual plane between the surfaces, where the pixel isolating portions are positioned to overlap the element isolating portions and have varying depths to enhance isolation and reduce noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If trenches are provided in the semiconductor layer to improve sensitivity and suppress color mixing, then the performance of the photoelectric conversion apparatus is improved, but the sensitivity may be limited or noise may increase depending on the positions at which the trenches are disposed
Solution Approach 1:
The isolating structure is divided into two distinct segments: element isolating portions (first isolating portions) that extend from the front surface to the back surface of the semiconductor layer, and pixel isolating portions (second isolating portions) that extend only partway through the semiconductor layer. This segmentation allows each portion to perform its specific isolation function optimally without interfering with the other, thereby improving overall performance while maintaining precise positioning control
Solution Approach 2:
Different regions of the semiconductor layer are provided with different isolating structures tailored to their specific needs. The element isolating portions are positioned at element boundaries to prevent color mixing between adjacent pixels, while the pixel isolating portions are positioned within pixel regions to suppress noise without compromising sensitivity. This localized optimization ensures that each area receives the appropriate level and type of isolation
2Object-affected harmful factors
If trenches are extended deeply into the semiconductor layer to improve isolation, then color mixing is suppressed, but sensitivity may be reduced due to excessive noise or lattice defects
Solution Approach 1:
The pixel isolating portions extend only partially through the semiconductor layer thickness, rather than completely. This partial action is sufficient to suppress color mixing and noise in the regions where it occurs, while avoiding the harmful effects of excessive trench depth such as lattice defects and increased noise generation. The element isolating portions do extend fully through the layer where complete isolation is necessary
Solution Approach 2:
The depth parameter of the isolating portions is varied based on position: element isolating portions have a depth equal to the full semiconductor layer thickness, while pixel isolating portions have a depth that is a subset of the full thickness. This parameter change optimizes the balance between isolation effectiveness and sensitivity preservation, preventing color mixing without generating excessive noise or defects
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 configuration improves the sensitivity and electrical characteristics of the photoelectric conversion apparatus by reducing color mixing and noise, while also preventing lattice defects and dark current, thereby enhancing the overall performance.
Implementation Method 1
As an isolating portion constituted by the groove acts as a barrier for light, an electric charge, and so on, the sensitivity improves, and color mixing is suppressed
Data Source
AI summary
A photoelectric conversion apparatus that includes a pixel region having photoelectric conversion elements includes a semiconductor layer having first and second surfaces, and the photoelectric conversion elements are disposed between the first and second surfaces. With a virtual plane extending along the second surface between the first and second surfaces being a third plane, the pixel region includes an element isolating portion constituted by an insulator disposed closer to the first surface than the third plane, and first and second isolating portions constituted by grooves provided in the semiconductor layer to pass through the third plane. The first isolating portion overlaps the element isolating portion in a normal direction to the third plane. An end of the second isolating portion on a side on the first surface is closer to the second surface than an end of the first isolating portion on a side on the first surface is.