Imaging Pixel Isolation Layout Using Refractive Index Boundaries
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional back-illuminated solid-state imaging devices suffer from color mixing between pixels due to obliquely incident light and light reflection from wiring layers, which deteriorates imaging performance.
Innovation Solution
Incorporating a first isolation part with a low refractive index region and a high refractive index region in the wiring layer, where the high refractive index region sandwiches the low refractive index region, to reflect light and prevent it from entering adjacent pixels, thereby confining light within each pixel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a high refractive index region is provided below the photoelectric conversion unit to reduce color mixing, then color mixing between pixels is reduced, but light may still enter adjacent pixels through the wiring layer when obliquely incident
Solution Approach 1:
The isolation structure is divided into two segments: an inter-element isolation part in the semiconductor substrate and a first isolation part in the wiring layer. This segmentation allows each part to address specific light propagation paths, with the first isolation part specifically targeting obliquely incident light that would otherwise enter adjacent pixels through the wiring layer.
Solution Approach 2:
The first isolation part extends the isolation concept into a new dimension by placing it in the wiring layer above the photoelectric conversion units. This vertical dimension addition creates multiple reflection interfaces that prevent light from propagating laterally through the wiring layer to adjacent pixels.
2Measurement precision
If the first isolation part includes a first low refractive index region and a first high refractive index region, then light is reflected at the boundary due to refractive index difference, but the structure complexity increases
Solution Approach 1:
The first isolation part utilizes refractive index parameter changes by incorporating both low refractive index regions (e.g., air gaps or low-k materials) and high refractive index regions (e.g., metal or high-k materials). This parameter variation creates strong reflection at the boundaries, efficiently confining light without requiring complex geometric structures.
3Measurement precision
If light is reflected by the wiring layer, then color mixing occurs between pixels, but adding isolation structures increases manufacturing complexity
Solution Approach 1:
The first isolation part is merged with the existing wiring layer structure, utilizing the same fabrication processes for forming metal lines and insulating films. The low refractive index regions are created using standard air gap or low-k dielectric techniques, while high refractive index regions use conventional metal layers, integrating the isolation function into the existing CMOS imaging device manufacturing flow.
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 arrangement effectively suppresses color mixing between pixels, improving imaging device performance by ensuring that light is confined within each pixel, enhancing imaging sensitivity.
Implementation Method 1
the light incident on the first high refractive index region of the first isolation part is reflected at a boundary between the first high refractive index region and the first low refractive index region due to a difference in refractive index between the first high refractive index region and the first low refractive index region
Data Source
AI summary
To provide an imaging device that can suppress color mixing between pixels. An imaging device includes a first semiconductor substrate having a plurality of photoelectric conversion elements, a lens body provided on one surface side of the first semiconductor substrate, and a wiring layer provided on an opposite side of the one surface of the first semiconductor substrate. The first semiconductor substrate includes an inter-element isolation part disposed between one photoelectric conversion element and another photoelectric conversion element adjacent to each other among the plurality of photoelectric conversion elements. The wiring layer includes a first isolation part disposed at a position facing the inter-element isolation part. The first isolation part includes a first low refractive index region and a first high refractive index region in contact with the first low refractive index region. The first high refractive index region sandwiches the first low refractive index region from both sides.