SPAD Scattering Structures for Photon Detection and Crosstalk Isolation
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Solution Overview
Problem
Conventional image sensors suffer from limited functionality, including inability to determine object distance, lower image quality, and lower than desired dynamic range, and single-photon avalanche diodes (SPADs) have susceptibility to crosstalk and limited dynamic range.
Innovation Solution
The implementation of SPAD-based semiconductor devices with passive or active quenching circuitry and light scattering structures to enhance photon detection efficiency and dynamic range, allowing for 3D imaging and improved image resolution through photon time-of-flight measurement and per-pixel readout capabilities.
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 is reduced and crosstalk susceptibility increases
Solution Approach 1:
The pixel array is divided into multiple independently controllable regions or groups, allowing different integration times or readout modes for different spatial zones. This segmentation enables the system to handle both very low light levels (single-photon detection) and higher light levels (extended dynamic range) simultaneously across different regions of the sensor array.
Solution Approach 2:
The system implements dynamic control of the SPAD operation mode, allowing switching between different integration times, gain settings, or readout configurations during operation. This dynamic adaptability enables the sensor to optimize its performance for the current lighting conditions while maintaining extended dynamic range capability through multi-exposure or multi-gain modes.
2Measurement precision
If single-photon avalanche diodes (SPADs) are used to improve sensitivity to incident light, then single-photon detection capability is achieved, but crosstalk susceptibility increases
Solution Approach 1:
Optical isolation structures or absorptive layers are introduced between adjacent SPAD pixels to absorb or block stray photons that would otherwise cause crosstalk. These intermediary elements act as barriers that prevent photons detected by one pixel from triggering false signals in neighboring pixels, thereby reducing crosstalk while maintaining single-photon detection sensitivity.
Solution Approach 2:
Different regions of the pixel array are equipped with varying degrees of optical isolation or shielding based on their specific crosstalk susceptibility. Areas with higher crosstalk risk receive enhanced isolation structures, while maintaining overall single-photon detection capability across the entire array through localized optimization.
3Adaptability or versatility
If conventional image sensors are used, then basic imaging functionality is achieved, but ability to determine object distance is lost and image quality is lower
Solution Approach 1:
The imaging system is designed to perform multiple functions using the same hardware platform: standard color imaging, depth mapping, and 3D reconstruction. By integrating time-of-flight measurement capability into conventional SPAD pixel architecture, the system achieves both basic imaging functionality and precise distance measurement without requiring separate dedicated sensors.
Solution Approach 2:
The system uses periodic modulation of the light source and synchronized gating of the SPAD detection to enable time-of-flight measurements. By modulating the illumination at known frequencies and measuring the phase shift or time delay of reflected light at each pixel, the system can determine object distance while maintaining continuous imaging capability.
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 solution enables effective low-light imaging, increased dynamic range, and improved image resolution by accurately measuring incident light and reducing cross-talk, thereby enhancing the functionality of imaging systems.
Implementation Method 1
a light scattering structure configured to scatter incident light, thereby increasing the path length of the incident light through the semiconductor substrate
Implementation Method 2
Each pixel typically includes a photosensitive element (such as a photodiode) that receives incident photons (light) and converts the photons into electrical signals
Implementation Method 3
Each pixel may also include a microlens that overlaps and focuses light onto the photosensitive element
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.