SPAD Scattering Structures for Higher Photon Detection and Lower Crosstalk
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Solution Overview
Problem
Conventional image sensors suffer from limited functionality, including inability to determine object distance, lower than desired image quality, and lower dynamic range, and single-photon avalanche diodes (SPADs) are susceptible to crosstalk and have limited dynamic range.
Innovation Solution
The use of SPADs with passive or active quenching circuitry and readout circuitry, including pulse counting and time-of-flight measurement, in combination with silicon photomultipliers and isolation and light scattering structures, to enhance photon detection efficiency and image resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If single-photon avalanche diodes (SPADs) are used to improve sensitivity to incident light, then single-photon detection capability is achieved, but dynamic range decreases and crosstalk susceptibility increases
Solution Approach 1:
The pixel array is divided into multiple independently controllable groups, where each group can be independently biased and controlled. This segmentation allows different regions to operate at different bias conditions, enabling simultaneous high-sensitivity single-photon detection in some regions while maintaining lower bias for reduced crosstalk and extended dynamic range in other regions.
Solution Approach 2:
The patent implements dynamic control of the bias voltage applied to different pixel groups through controllable bias circuitry. The bias condition can be adjusted in real-time based on imaging requirements, allowing the system to switch between high-sensitivity mode (for single-photon detection) and low-crosstalk mode (for extended dynamic range), thereby adapting to different imaging scenarios.
2Measurement precision
If single-photon avalanche diodes (SPADs) are used to improve sensitivity to incident light, then single-photon detection capability is achieved, but susceptibility to crosstalk increases
Solution Approach 1:
The pixel array is divided into multiple independently controllable groups, where each group can be independently biased and controlled. This segmentation allows different regions to operate at different bias conditions, enabling simultaneous high-sensitivity single-photon detection in some regions while maintaining lower bias for reduced crosstalk and extended dynamic range in other regions.
Solution Approach 2:
The patent extracts and removes excess charge carriers that cause crosstalk through controlled charge injection and extraction mechanisms. By actively managing charge carrier populations in each pixel group, the system can maintain high detection sensitivity while removing the harmful charge carriers that would otherwise cause crosstalk between adjacent pixels.
3Adaptability or versatility
If conventional image sensors are used, then functionality is maintained, but image quality and resolution are lower than desired
Solution Approach 1:
The patent creates a multi-functional imaging system that can operate in multiple modes: single-photon detection mode for high-sensitivity low-light imaging, conventional imaging mode for standard applications, and depth imaging mode using time-of-flight measurements. This universal approach allows the same hardware platform to deliver superior image quality and resolution across different application scenarios while maintaining broad functionality.
Solution Approach 2:
The patent adds the time dimension to traditional spatial imaging by implementing time-of-flight measurement capabilities. This allows the system to capture not only the intensity and color information conventional sensors provide but also depth information, creating 3D images and enabling new imaging functionalities that significantly enhance image quality and provide additional dimensional data.
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 approach improves the dynamic range and image quality by accurately measuring incident light and enabling 3D imaging, while minimizing crosstalk and increasing the probability of photon detection, thereby enhancing the functionality of imaging systems.
Implementation Method 1
scattering structures configured to scatter incident light, thereby increasing the path length of the light through the semiconductor substrate and increasing the probability of the incident light being absorbed by the semiconductor
Data Source
AI summary
An imaging device may include single-photon avalanche diodes (SPADs). To improve the sensitivity and signal-to-noise ratio of the SPADs, light scattering structures may be formed in the semiconductor substrate to increase the path length of incident light through the semiconductor substrate. The light scattering structures may include a low-index material formed in trenches in the semiconductor substrate. The light scattering structures may have different sizes and/or a layout with a non-uniform number of structures per unit area. SPAD devices may also include isolation structures in a ring around the SPADs to prevent crosstalk. The isolation structures may include metal-filled deep trench isolation structures. The metal filler may include tungsten.