SPAD Isolation and Light Scattering Structures for Crosstalk Control
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Solution Overview
Problem
Conventional image sensors face limitations in determining object distance and achieving desired image quality and resolution, and single-photon avalanche diodes (SPADs) struggle with dynamic range due to reset time constraints at higher light levels.
Innovation Solution
The use of SPADs with passive or active quenching circuitry and silicon photomultipliers, where multiple SPADs are grouped together to enhance photon detection efficiency and dynamic range, combined with light scattering structures and isolation structures to improve absorption and prevent crosstalk, allows for improved light detection and 3D imaging 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 reset time constraints limit dynamic range at higher light levels
Solution Approach 1:
The patent divides the detection system into multiple SPADs grouped together in arrays, where each SPAD operates independently but contributes to the overall detection capability. This segmentation allows the system to handle higher light levels by distributing the detection load across multiple elements, thereby expanding dynamic range while maintaining single-photon sensitivity.
Solution Approach 2:
The patent implements dynamic control of SPAD operation through adjustable bias voltages and quenching mechanisms. By dynamically adjusting the bias voltage below breakdown voltage during high light conditions and approaching breakdown voltage during low light conditions, the system adapts its sensitivity to maintain optimal dynamic range across varying light levels.
2Measurement precision
If multiple SPADs are grouped together to enhance photon detection efficiency, then detection efficiency and dynamic range increase, but crosstalk between adjacent SPADs occurs
Solution Approach 1:
The patent extracts and removes the harmful crosstalk effect by implementing isolation structures between adjacent SPADs. These isolation structures, such as deep trench isolation or epitaxial isolation layers, physically separate the SPAD elements and block the propagation of avalanche carriers between neighboring devices, thereby eliminating crosstalk while maintaining close spacing for high detection efficiency.
Solution Approach 2:
The patent introduces intermediary isolation structures between adjacent SPADs that act as mediators to prevent direct interaction between neighboring elements. These isolation structures, including doped semiconductor layers or dielectric materials, serve as barriers that block carrier diffusion and reduce optical coupling, thereby preventing crosstalk while allowing the SPADs to remain closely spaced for efficient photon detection.
3Adaptability or versatility
If conventional image sensors are used, then basic imaging functionality is achieved, but ability to determine object distance and achieve desired image quality is limited
Solution Approach 1:
The patent makes the image sensor universal by integrating multiple functions into a single device. The sensor array can operate in both conventional imaging mode and time-of-flight depth sensing mode, allowing it to perform basic imaging while simultaneously determining object distances. This multi-functionality is achieved through the SPAD-based pixel design that can measure both photon intensity and photon arrival time.
Solution Approach 2:
The patent implements periodic modulation of the light source and synchronized gating of the SPAD detection windows to enable time-of-flight measurements. By periodically modulating the illumination and opening detection gates at specific intervals, the system can measure the time delay of reflected light to determine object distance, while also capturing conventional intensity-based images during the integration period.
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 low-light imaging, increased dynamic range, and high-resolution 3D scene reproduction by enhancing the probability of photon detection and reducing reset time limitations, thereby improving image quality and depth sensing.
Implementation Method 1
single-photon avalanche diodes (SPADs) for single photon detection
Implementation Method 2
light scattering structures to improve absorption
Implementation Method 3
isolation structures to prevent crosstalk
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. To mitigate crosstalk, multiple rings of isolation structures may be formed around the SPAD. An outer deep trench isolation structure may include a metal filler such as tungsten and may be configured to absorb light. The outer deep trench isolation structure therefore prevents crosstalk between adjacent SPADs. Additionally, one or more inner deep trench isolation structures may be included. The inner deep trench isolation structures may include a low-index filler to reflect light and keep incident light in the active area of the SPAD.