Image Sensor Deep Trenches with Negative Charge Layer
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Highly integrated image sensors face cross-talk issues due to the scaling down of pixels, leading to increased dark current and white spot occurrences.
Innovation Solution
The image sensor design incorporates a substrate with deep trenches and a negative fixed charge layer, including metal oxides like Hafnium, to separate pixel regions and reduce dark current, along with a shallow device isolation layer and a filling insulation layer to enhance light sensitivity and reduce cross-talk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If pixels are scaled down to achieve high integration, then device integration is improved, but cross-talk between pixels increases
Solution Approach 1:
The substrate is divided into multiple pixel regions by deep trenches that extend from the second surface toward the first surface. These trenches physically segment the pixel regions, preventing electrical and optical interference between adjacent pixels while maintaining high integration density.
Solution Approach 2:
A negative fixed charge layer is introduced as an intermediary material within the deep trenches. This layer acts as a mediator to actively suppress carrier generation and reduce dark current, thereby preventing cross-talk between pixels more effectively than passive isolation alone.
2Object-generated harmful factors
If deep trenches are formed to separate pixel regions, then cross-talk is reduced, but manufacturing complexity increases
Solution Approach 1:
The deep trenches are formed early in the fabrication process, before other device structures are built. This preliminary action establishes the pixel region boundaries first, allowing subsequent layers to be formed within defined boundaries, which simplifies overall manufacturing despite the deep trench formation step.
Solution Approach 2:
The deep trench structure combines multiple materials: the trench itself (empty space or filled with insulation), the negative fixed charge layer (metal oxide material), and surrounding substrate materials. This composite structure achieves effective pixel isolation through material properties rather than just geometric depth, potentially simplifying the trench formation process.
3Object-generated harmful factors
If negative fixed charge layer is added to reduce dark current, then dark current is reduced, but device complexity increases
Solution Approach 1:
The negative fixed charge layer serves multiple functions simultaneously: it reduces dark current by suppressing carrier generation, provides additional isolation between pixels, and can serve as a structural element within the deep trench. This multi-functionality justifies the added layer without proportionally increasing complexity.
Solution Approach 2:
The invention changes the electrical parameter of the substrate by introducing fixed negative charges into the deep trench region. This parameter change (electrical charge density) actively suppresses dark current generation without requiring significant structural modifications, thereby reducing dark current with minimal complexity increase.
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 and white spot occurrences by creating a deep device isolation layer that separates pixel regions and improves light sensitivity, thereby enhancing the overall performance of the image sensor.
Implementation Method 1
a negative fixed charge layer covering the second surface of the substrate and at least a portion of a sidewall of the deep trench is also provided
Data Source
AI summary
Image sensors are provided including a substrate defining a plurality of pixel regions, the substrate having a first surface and a second surface opposite the first surface. The second surface of the substrate is configured to receive light incident thereon and the substrate defines a deep trench extending from the second surface of the substrate toward the first surface substrate and separating the plurality of pixel regions from each other. In each of the plurality of pixel regions of the substrate, a photoelectric conversion region is provided. A gate electrode is provided on the photoelectric conversion region and a negative fixed charge layer covering the second surface of the substrate and at least a portion of a sidewall of the deep trench is also provided. The image sensors further include a shallow device isolation layer on the first surface of the substrate. The shallow device isolation layer defines an active region in each of the pixel regions and the negative fixed charge layer contacts the shallow device isolation layer.