Dual Transmission Gate Pixel Layout for Low-Noise Image Sensors
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Solution Overview
Problem
As image sensors integrate more pixels, the size of each component decreases, leading to increased noise and decreased image quality due to leakage currents in the pixel circuit.
Innovation Solution
The image sensor design includes a substrate with pixels featuring a photoelectric conversion region and a floating diffusion region, along with pixel transistors having first and second transmission gates with different widths and heights, where the second transmission gate is smaller, reducing noise and improving source follower gain characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the size of each pixel and component is decreased to increase integration, then the number of pixels increases, but leakage current increases and image quality decreases
Solution Approach 1:
The patent applies local quality by making the second transmission gate have a smaller width than the first transmission gate. This local differentiation in gate dimensions optimizes the specific region where leakage current occurs, allowing the smaller gate to reduce leakage and noise in that critical area while the overall pixel structure maintains high integration through other design features.
Solution Approach 2:
The patent changes the parameter of transmission gate width, specifically making the second transmission gate narrower than the first. This parameter modification directly addresses the leakage current issue by reducing the gate area that contributes to leakage, thereby improving image quality while maintaining the high integration design.
2Productivity
If the size of each pixel and component is decreased to increase integration, then the number of pixels increases, but noise increases and image quality decreases
Solution Approach 1:
The patent applies local quality by making the second transmission gate have a smaller width than the first transmission gate. This local differentiation in gate dimensions optimizes the specific region where noise is generated, allowing the smaller gate to reduce noise in that critical area while the overall pixel structure maintains high integration through other design features.
Solution Approach 2:
The patent changes the parameter of transmission gate width, specifically making the second transmission gate narrower than the first. This parameter modification directly addresses the noise issue by reducing the gate area that generates noise, thereby improving image quality while maintaining the high integration design.
3Object-generated harmful factors
If transmission gates are made smaller to reduce noise, then noise decreases, but the area available for other components decreases
Solution Approach 1:
The patent applies local quality by making only the second transmission gate smaller than the first, rather than reducing all gate sizes uniformly. This selective size reduction targets the specific area where noise is most problematic while preserving sufficient area in other regions for other pixel components, thus balancing noise reduction with area availability.
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 reduces noise and improves image quality by minimizing local interference during ion implantation and achieving a potential hump-free potential profile, enhancing the movement of electrons from the photoelectric conversion region to the floating diffusion region.
Implementation Method 1
Each pixel may include a photodiode region and a pixel circuit. The pixel circuit receives incident light and converts the light into an electrical signal.
Data Source
AI summary
An image sensor includes a substrate having a plurality of pixels. Each pixel includes a photoelectric conversion region and a floating diffusion region in the substrate, a pixel transistor including a pixel gate on the first surface of the substrate, a first transmission gate between the photoelectric conversion region and the floating diffusion region, extending into the substrate, and having a first width in a horizontal direction, and a second transmission gate between the photoelectric conversion region and the floating diffusion region, arranged between the pixel gate and the first transmission gate when viewed in a plan view, and having a second width less than the first width in the horizontal direction.