Solid-State Imaging Device Uniform Potential Distribution
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In CMOS line sensors, the miniaturization of pixel pitch leads to a decrease in photodiode opening ratio and sensitivity, and when the floating diffusion of transfer transistors is shared among three or more adjacent pixels, the varying distances to the center of the floating diffusion cause uneven potential distribution and characteristic variations.
Innovation Solution
The design includes separate but electrically connected diffusion layers for each transfer transistor, ensuring that the potential distributions are uniform across the pixels from the photodiode of the transfer transistor to the floating diffusion, achieved by maintaining similar shapes, areas, and distances of the diffusion layers and gate electrodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If the floating diffusion of transfer transistors is shared among three or more adjacent pixels to increase the photodiode opening ratio, then the opening ratio and sensitivity are improved, but the distances from respective transfer transistors to the center of the floating diffusion differ causing uneven potential distribution and characteristic variations
Solution Approach 1:
The patent divides the shared floating diffusion into multiple separate diffusion layers (first diffusion layer, second diffusion layer, third diffusion layer) corresponding to each transfer transistor. Each diffusion layer is positioned at a specific distance from its respective transfer transistor, segmenting the originally unified floating diffusion structure to eliminate potential distribution variations while maintaining the shared output functionality.
Solution Approach 2:
The patent applies local quality by making each diffusion layer have specific local characteristics - the first diffusion layer is positioned at a first distance from the first transfer transistor, the second diffusion layer at a second distance from the second transfer transistor, and so on. This local positioning ensures that each transfer transistor has an optimized potential distribution in its local region, while all diffusion layers are electrically connected to achieve uniform potential across the entire structure.
2Productivity
If the pixel pitch is miniaturized to increase the number of pixels, then the pixel density is improved, but the photodiode opening ratio decreases and sensitivity decreases
Solution Approach 1:
The patent resolves the pixel pitch miniaturization problem by transitioning from a planar shared floating diffusion to a multi-layer diffusion structure. By stacking multiple diffusion layers in the vertical dimension and connecting them electrically, the patent achieves uniform potential distribution without requiring a larger lateral area, thus maintaining high pixel density while improving photodiode opening ratio.
3Device complexity
If a single shared floating diffusion is used for three or more pixels, then the device complexity is reduced, but the characteristic uniformity between pixels deteriorates
Solution Approach 1:
The patent segments the single shared floating diffusion into multiple separate diffusion layers, each with specific positioning relative to its transfer transistor. This segmentation improves characteristic uniformity by ensuring each pixel has an optimized local potential distribution, while the electrical connection between layers maintains the shared output functionality, balancing complexity and uniformity.
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 uniformity of potential distributions and reduces characteristic variations between pixels, even when the output portion of photodiodes is shared, enhancing the imaging performance by maintaining consistent charge transfer.
Implementation Method 1
a first photodiode, a first gate electrode, and a first diffusion layer; a second transfer transistor including a second photodiode, a second gate electrode, and a second diffusion layer; a third transfer transistor including a third photodiode, a third gate electrode, and a third diffusion layer
Data Source
AI summary
In this solid-state imaging device, the sameness of the potential distributions in pixels, in a region from a photodiode of a transfer transistor to a floating diffusion in a charge transfer path, is improved. The solid-state imaging device includes a first transfer transistor including a first photodiode, a first gate electrode, and a first floating diffusion, a second transfer transistor including a second photodiode, a second gate electrode, and a second floating diffusion, a third transfer transistor including a third photodiode, a third gate electrode, and a third floating diffusion, and a reset transistor including a diffusion layer, which is a source or drain region, and a reset gate. The first to third floating diffusions and the diffusion layer of the reset transistor are separated from each other, and are electrically connected to each other via an interconnect. The first to third photodiodes are arrayed one-dimensionally.