Ring-Shaped ToF Sensor Pixel Structure for Photocharge Capture
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Solution Overview
Problem
Current image sensing devices, particularly those using the Time of Flight (ToF) method for distance measurement, face challenges in achieving high sensitivity and demodulation contrast due to limitations in pixel design and circuitry, especially in capturing and processing photocharge effectively.
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, arranged in a ring shape to surround the control node, enhancing the capture of hole currents and improving photocharge detection and processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional pixel design is used, then device complexity is reduced, but sensitivity and demodulation contrast deteriorate
Solution Approach 1:
The pixel is divided into multiple functional regions: a control node region for generating hole current, a detection node region for capturing photocharge, and a low resistance region with dielectric layer. This segmentation allows each region to perform its specific function optimally, improving sensitivity while maintaining manageable complexity through functional specialization.
Solution Approach 2:
Different regions of the pixel are given different electrical properties: the control node region has high resistance to maintain voltage potential, the detection node region has optimized geometry for photocharge capture, and the low resistance region provides efficient charge transport paths. This local differentiation of electrical characteristics enhances overall pixel performance.
2Measurement precision
If conventional pixel design is used, then manufacturing is simpler, but demodulation contrast deteriorates
Solution Approach 1:
The detection node is designed with a ring shape that surrounds the control node, creating a nested configuration where the detection node encloses the control node. This nested structure improves demodulation contrast by optimizing the spatial relationship between charge generation and detection regions while following a systematic fabrication approach.
Solution Approach 2:
The pixel structure extends into the vertical dimension with the low resistance region including a dielectric layer formed at specific depths in the substrate. The depth of the depletion region under the detection node is larger than the depth of the dielectric layer, creating a three-dimensional charge collection volume that enhances demodulation contrast.
3Productivity
If ring-shaped detection node surrounds control node, then photocharge capture is improved, but device complexity increases
Solution Approach 1:
The control node generates hole current in advance to create an electric field that guides photocharge toward the detection node before photocharge arrives. This preliminary action of establishing the charge carrier flow improves photocharge capture efficiency by pre-positioning the electrical environment for optimal charge collection.
Solution Approach 2:
The low resistance region acts as an intermediary between the control node and the surrounding circuitry, providing a dedicated path for hole current flow. This intermediary structure facilitates efficient charge transport while isolating the core detection mechanism from external circuit complexities.
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 the sensitivity and demodulation contrast of the pixels, enabling more effective distance measurement and image sensing by optimizing the flow of hole currents and photocharge capture, thereby enhancing the overall performance of the image sensing device.
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.