Pixel Source Follower Layout for Lower Image Sensor Noise
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Solution Overview
Problem
Image sensors face challenges in reducing signal noise, particularly thermal noise and flicker noise, which affect image quality due to the inherent characteristics of source follower transistors.
Innovation Solution
The design incorporates a source follower transistor with one source region and two drain regions adjacent to the source follower gate electrode, operating in a parallel structure to reduce noise and increase current sensitivity, while also utilizing pixel separation parts and impurity regions to enhance noise reduction and integration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If source follower transistors are used in conventional image sensors, then pixel integration is achieved, but thermal noise and flicker noise increase
Solution Approach 1:
The source follower transistor is segmented into one source region and two drain regions, creating a parallel structure that divides the current path. This segmentation reduces the noise impact by distributing the signal across multiple paths while maintaining integration functionality.
Solution Approach 2:
Different regions of the transistor are assigned different functions: the source region handles signal input while the two drain regions provide parallel output paths. This local differentiation optimizes noise characteristics in specific areas while preserving overall pixel integration.
2Ease of manufacture
If conventional transistor structures are used, then manufacturing simplicity is maintained, but noise reduction capability is limited
Solution Approach 1:
The transistor structure is divided into standard semiconductor regions (source and two drains) that can be manufactured using conventional photolithography and doping processes, maintaining ease of manufacture while achieving noise reduction through the parallel configuration.
Solution Approach 2:
The transistor parameters are modified by creating an asymmetric structure with one source region and two drain regions, changing the electrical characteristics to reduce noise while maintaining compatibility with standard manufacturing processes.
3Productivity
If pixels are closely integrated, then sensor density increases, but noise from adjacent pixels may increase
Solution Approach 1:
The pixel separation part is segmented into multiple sidewalls (first to fourth sidewalls) that create distinct boundaries between adjacent pixels. This segmentation effectively isolates noise from neighboring pixels while maintaining high sensor density through efficient space utilization.
Solution Approach 2:
The pixel separation structure uses asymmetric positioning of impurity regions relative to the source follower gate electrode, creating optimized noise barriers that prevent interference from adjacent pixels while allowing close integration.
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 effectively reduces thermal noise and flicker noise, improving image quality and sensitivity, and allows for a more integrated and efficient image sensing process.
Implementation Method 1
The photodiode serves to convert incident light into an electrical signal
Data Source
AI summary
An image sensor includes a pixel separation part in a substrate and configured to separate pixels, the pixels including a first pixel, the pixel separation part including first to fourth sidewalls that at least partially define the first pixel, a first source follower gate electrode on the first pixel and adjacent to the first sidewall and the second sidewall, a first impurity region adjacent to a first corner where the first sidewall and the second sidewall meet, a second impurity region adjacent to a second corner where the second sidewall and the third sidewall meet, and a third impurity region adjacent to a third corner where the first sidewall and the fourth sidewall meet. The first to third impurity regions are adjacent to the first source follower gate electrode. The second impurity region and the third impurity region are electrically connected to each other.