Pixel Overflow-Drain Structure for ToF Background Noise Control
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Solution Overview
Problem
Existing optical detectors in indirect Time-of-Flight distance measurement systems face significant background noise issues, particularly under strong ambient light conditions, leading to oversaturation of memory nodes and affecting signal accuracy, which current solutions like optical filters, multi-frame fusion, and background suppression circuits either fail to adequately address or complicate with increased power consumption and reduced spatial resolution.
Innovation Solution
The introduction of overflow doping regions on the substrate's second surface, corresponding to memory nodes, with vertically-formed overflow-drain structures to discharge stored charges at a controlled rate, reducing oversaturation without altering exposure time or power consumption, and maintaining pixel unit area and resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If optical filters are used to reduce background noise, then signal accuracy is improved, but device complexity and power consumption increase
Solution Approach 1:
The patent extracts the harmful background noise directly at the memory node level by introducing overflow doping regions that selectively discharge accumulated charges. This removes the need for complex optical filters and achieves noise reduction at the source rather than requiring additional filtering components.
Solution Approach 2:
The overflow doping regions act as intermediary structures between the memory nodes and the substrate, providing a controlled discharge path for excess charges. This intermediary mechanism selectively removes background noise while preserving signal charges, achieving noise reduction without complex filtering systems.
2Measurement precision
If multi-frame fusion is used to suppress background noise, then signal accuracy is improved, but exposure time and processing complexity increase
Solution Approach 1:
The patent implements preliminary action by pre-configuring overflow doping regions and overflow interconnection structures that are ready to immediately discharge excess charges during strong ambient light conditions. This eliminates the need for post-processing multi-frame fusion and extends the effective exposure time without sacrificing signal accuracy.
3Measurement precision
If background suppression circuits are used, then signal accuracy is improved, but power consumption increases
Solution Approach 1:
The overflow doping regions provide self-service background noise suppression by automatically discharging excess charges through the overflow interconnection structures when background noise accumulates. This passive, self-regulating mechanism eliminates the need for active background suppression circuits and their associated power consumption.
4Measurement precision
If memory nodes are used to store photogenerated carriers, then phase calculation capability is improved, but area occupation increases
Solution Approach 1:
The patent resolves the area conflict by extending the overflow doping regions into the substrate depth (second dimension/third dimension) rather than expanding them laterally on the surface. This vertical integration allows multiple memory nodes to share overflow structures, reducing the lateral area occupation while maintaining phase calculation capabilities.
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
Effectively reduces background noise in optical detectors by preventing oversaturation of memory nodes, enhancing signal accuracy without increasing power consumption or compromising spatial resolution, thus improving the performance of optical detectors under various lighting conditions.
Implementation Method 1
A plurality of overflow doping regions are in the second surface of the substrate. The locations of the plurality of overflow doping regions correspond to locations of the plurality of memory nodes, and a doping type of the plurality of overflow doping regions is same as a doping type of the plurality of doping regions of the plurality of memory nodes.
Implementation Method 2
A photosensitive element is in the first surface of the substrate
Data Source
AI summary
A pixel unit includes: a base, the base including a substrate, a photosensitive element, and memory nodes; overflow doping regions in the second surface of the substrate; and overflow interconnection structures electrically connected to the overflow doping regions. Vertical-overflow-drain structures are formed between the overflow doping regions and the memory nodes, allowing the charge stored in the memory nodes to be discharged at a certain rate through the overflow interconnection structures. This configuration reduces the oversaturation of memory nodes effectively without altering the exposure time or affecting circuit power consumption, thereby addressing background noise issue. Furthermore, the memory nodes and the overflow doping regions are in the first and second surfaces of the substrate, respectively. Therefore, the placement of the overflow doping regions does not affect the area of the pixel unit, and the resolution of the photosensor is preserved.