SPAD Light Scattering Structures for Low-Light Depth Imaging
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Solution Overview
Problem
Conventional image sensors suffer from limited functionality, including inability to determine object distance and lower-than-desired image quality and resolution, which is addressed by incorporating single-photon avalanche diodes (SPADs) for improved light sensitivity and depth sensing.
Innovation Solution
The implementation of SPADs in imaging systems, including passive and active quenching circuitry, readout circuitry for photon counting and time-of-flight measurement, and the use of silicon photomultipliers to enhance dynamic range and resolution by detecting single photons and measuring photon time-of-flight for 3D imaging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional photodiodes are used in image sensors, then the device structure is simple and manufacturing is easier, but the sensitivity to incident light is insufficient and single-photon detection capability is lost
Solution Approach 1:
The patent changes the operating parameters of the photodiode by applying reverse bias voltage to operate in avalanche breakdown mode, transforming conventional photodiodes into SPADs capable of single-photon detection. This parameter change enables high sensitivity while maintaining the basic photodiode structure.
Solution Approach 2:
The patent implements periodic quenching of the avalanche breakdown through control circuitry that periodically resets the reverse bias voltage after photon detection. This periodic action enables continuous single-photon detection capability while managing the complex avalanche process.
2Adaptability or versatility
If conventional image sensors are used, then the manufacturing process is simpler, but the ability to determine object distance and achieve 3D imaging is lost
Solution Approach 1:
The patent makes the image sensor multi-functional by integrating both 2D imaging photodiodes and 3D depth-sensing SPADs in the same device. This universality allows the sensor to perform both conventional imaging and time-of-flight depth measurement, eliminating the need for separate depth-sensing hardware.
Solution Approach 2:
The patent merges the 2D imaging function and 3D depth sensing function into a single integrated sensor device. By combining conventional photodiodes for imaging with SPADs for time-of-flight measurement on the same substrate, the system achieves both functionalities with shared readout circuitry and processing.
3Productivity
If conventional photodiodes are used, then the dynamic range is limited, but the device complexity is lower
Solution Approach 1:
The patent segments the sensor into distinct regions with different photodiode types: conventional photodiodes for standard imaging and SPAD-based photodiodes for low-light and depth-sensing applications. This segmentation allows each region to optimize its performance for specific conditions, expanding the overall dynamic range of the imaging system.
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 enables effective imaging in low light conditions, improves image data accuracy, and increases the dynamic range of imaging systems by accurately measuring incident light, allowing for higher resolution and depth sensing capabilities.
Implementation Method 1
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 2
single-photon avalanche diodes (SPADs) for single photon detection
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. One or more microlenses may focus light onto the semiconductor substrate. Areas of the semiconductor substrate that receive more light from the microlenses may have a higher density of light scattering structures to optimize light scattering while mitigating dark current.