ToF Image Sensor Pixel Layout for Higher Demodulation Contrast
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Solution Overview
Problem
Current image sensing devices, particularly CMOS sensors, face challenges in achieving high sensitivity and demodulation contrast for accurate distance measurement in applications like automotive and medical devices, especially when using the Time of Flight (ToF) method.
Innovation Solution
The proposed image sensing device incorporates CAPD pixels with a specific pixel array structure featuring a control node, a detection node, and a low resistance region with a dielectric layer, allowing for improved hole current control and enhanced photocharge detection, which improves sensitivity and demodulation contrast.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional pixel structures are used, then device complexity is reduced, but sensitivity and demodulation contrast deteriorate
Solution Approach 1:
The pixel is divided into multiple functional regions including a control node, detection node, and multiple low resistance regions (first and second low resistance regions). This segmentation allows independent optimization of each region's function, enabling precise control of hole current flow paths while maintaining manageable device complexity through modular design.
Solution Approach 2:
Different regions of the pixel are assigned different electrical properties: the control node generates hole current, the detection node captures photocharge, and the low resistance regions provide preferential current paths. This local differentiation of functional qualities enables enhanced sensitivity and demodulation contrast by optimizing each region's contribution to the overall pixel performance.
2Measurement precision
If conventional pixel structures are used, then device complexity is reduced, but demodulation contrast deteriorates
Solution Approach 1:
The pixel structure is segmented into distinct functional zones including control nodes for hole current generation, detection nodes for photocharge capture, and low resistance regions for current path control. This segmentation enables independent optimization of demodulation contrast through precise control of charge migration paths without requiring complete redesign of the entire device.
Solution Approach 2:
The low resistance regions are strategically positioned to create preferential paths for hole current flow, enhancing the demodulation contrast by ensuring that photocharge migrates along controlled trajectories. This local optimization of electrical properties in specific regions improves demodulation performance without proportionally increasing overall device complexity.
3Measurement precision
If hole current flow is not controlled, then device complexity is reduced, but sensitivity deteriorates
Solution Approach 1:
Low resistance regions are introduced at specific locations within the pixel to create preferential paths for hole current flow. These localized modifications to electrical properties enable precise control of current trajectories, ensuring that photocharge migrates along optimal paths to the detection node, thereby enhancing sensitivity without requiring complex global control mechanisms.
Solution Approach 2:
The low resistance regions act as intermediary structures that mediate the flow of hole current between the control node and detection node. By providing preferential current paths, these intermediary regions guide charge migration in a controlled manner, improving sensitivity while maintaining relatively simple device architecture.
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 enables more accurate and efficient distance measurement by improving the sensitivity and demodulation contrast of the pixels, effectively addressing the limitations of existing CMOS sensors in ToF applications.
Implementation Method 1
a control node configured to generate a hole current in a substrate
Implementation Method 2
a detection node configured to capture photocharge migrated by the hole current
Data Source
AI summary
An image sensing device is provided to include a pixel array having a plurality of pixels arranged in a matrix shape. Each of the pixels includes: a control node configured to generate a hole current in a substrate; a detection node configured to capture photocharge migrated by the hole current, formed in a shape whose at least part is partially open, and disposed to surround the control node, and a low resistance region including a dielectric layer formed in the substrate, and disposed in the opening on of the detection node. The low resistance region includes an inner low resistance region disposed between the control node and the center of the pixel.