Image Sensor Pixel Structure With Vertical Multi-Gate Charge Transfer
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Solution Overview
Problem
Current image sensors face challenges in achieving improved image quality due to limitations in pixel design and transfer efficiency, particularly in handling varying light conditions and dynamic ranges.
Innovation Solution
The image sensor incorporates a novel pixel structure with a first sub-pixel and a second sub-pixel, each equipped with a photoelectric conversion area, floating diffusion area, and transfer transistors, where the second transfer transistor features a vertical multi-gate, enhancing charge transfer efficiency and dynamic range handling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional transfer transistors are used in pixel design, then device complexity is reduced, but charge transfer efficiency and dynamic range handling deteriorate
Solution Approach 1:
The transfer gate is extended from a conventional planar two-dimensional structure into the vertical third dimension, creating a multi-gate structure that wraps around the channel. This vertical extension increases the gate-channel interaction area without increasing the planar footprint, thereby improving charge transfer efficiency while maintaining compact pixel design
Solution Approach 2:
The multi-gate structure is formed by nesting multiple gate layers around a central channel region. The gates are arranged in a nested configuration where inner gates surround the channel and outer gates provide additional control, creating a compact three-dimensional transistor structure that enhances transfer efficiency
2Reliability
If pixel area is increased to improve dynamic range, then full well capacity increases, but pixel density and resolution deteriorate
Solution Approach 1:
The transfer gate structure extends vertically into the third dimension, increasing the effective gate area and charge control capability without increasing the horizontal pixel footprint. This allows enhanced dynamic range and full well capacity to be achieved within the same planar pixel area, maintaining high pixel density
3Measurement precision
If conventional single-gate transfer transistors are used, then manufacturing process is simpler, but charge transfer efficiency and signal-to-noise ratio deteriorate
Solution Approach 1:
The transfer gate is formed by extending gate structures vertically and arranging multiple gates in a nested configuration around the channel. This three-dimensional arrangement increases the gate-channel interaction area, improving charge transfer efficiency and signal-to-noise ratio while using standard semiconductor fabrication processes
Solution Approach 2:
The nested multi-gate structure serves multiple functions simultaneously: it provides enhanced charge transfer control, increased capacitive coupling, improved signal-to-noise ratio, and compact area utilization. The same structural configuration achieves multiple performance goals without requiring separate components
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 improves image quality by increasing signal-to-noise ratio and dynamic range, enabling better performance across different illuminance levels and enhancing the full well capacity of the image sensor.
Implementation Method 1
The photodiode may convert incident light thereto into an electrical signal
Data Source
AI summary
An image sensor including a plurality of pixels, wherein each pixel of the plurality of pixels comprises: a first sub-pixel comprising a first photoelectric conversion area, a first floating diffusion area, and a first transfer transistor configured to transfer charges accumulated in the first photoelectric conversion area to the first floating diffusion area; and a second sub-pixel disposed adjacent to the first sub-pixel and comprising a second photoelectric conversion area, a second floating diffusion area and a second transfer transistor configured to transfer charges accumulated in the second photoelectric conversion area to the second floating diffusion area, wherein the first transfer transistor comprises a first transfer gate, wherein the second transfer transistor comprises a second transfer gate, and wherein the second transfer gate comprises a vertical multi-gate