SPAD Light-Spreading Lens Layout for Higher 3D Imaging Dynamic Range
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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) that can detect single photons and measure photon time-of-flight for 3D imaging.
Innovation Solution
The use of SPADs in imaging systems, including passive and active quenching circuitry to control avalanche breakdown, and grouping multiple SPADs into silicon photomultipliers to enhance dynamic range and accuracy, along with the integration of light spreading lenses to reduce photon density and increase saturation levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional photodiodes are used in image sensors, then the device structure is simple and manufacturing is easy, but the sensitivity to incident light is insufficient and single-photon detection is not achieved
Solution Approach 1:
The patent changes the operating parameters of the photodiode by applying reverse bias voltage above the breakdown voltage, transforming it from a conventional photodiode operation mode to an avalanche breakdown mode. This parameter change enables single-photon detection capability while maintaining the basic photodiode structure, thus improving sensitivity without proportionally increasing device complexity
Solution Approach 2:
The patent divides the photodiode structure into distinct functional regions including the avalanche region and the collection region, with specific doping profiles (first doped region, second doped region, third doped region). This segmentation allows each region to perform its specific function efficiently, achieving high sensitivity through optimized charge carrier generation and collection while keeping the overall structure manageable
2Adaptability or versatility
If conventional image sensors are used, then the device is simple to operate, 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 enabling it to perform both conventional 2D imaging and time-of-flight measurements for 3D reconstruction. The same photodiode array structure is used for both functions, with the added capability of measuring photon arrival times. This universality allows the device to determine object distance while maintaining image quality, achieving enhanced functionality without requiring separate dedicated hardware systems
3Measurement precision
If multiple photons are focused onto a small area of SPADs, then the detection area is concentrated, but the photon density increases causing saturation and reduced dynamic range
Solution Approach 1:
The patent addresses the photon density problem by spreading photons across multiple spatial dimensions - distributing them across a larger array of SPAD pixels in the lateral direction and across multiple time bins in the temporal direction. This dimensional distribution reduces the photon density at any single SPAD location, preventing saturation and extending the dynamic range while maintaining overall detection accuracy through the combined signal from multiple pixels and time bins
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 improved sensitivity in low light conditions, increased dynamic range, and higher resolution imaging by effectively detecting single photons and measuring photon time-of-flight, thereby enhancing image quality and allowing for 3D scene reconstruction.
Implementation Method 1
single-photon avalanche diodes (SPADs) for single photon detection
Implementation Method 2
single-photon avalanche diodes may be capable of single-photon detection
Implementation Method 3
integration of light spreading lenses to reduce photon density and increase saturation levels
Data Source
AI summary
An imaging device may include single-photon avalanche diodes (SPADs). The single-photon avalanche diodes may be arranged in a one-dimensional or two-dimensional array in a SPAD-based semiconductor device. The SPAD-based semiconductor device may also include a transparent cover glass that is formed over the array of SPADs. Each line of SPADs within the SPAD-based semiconductor device may be covered by a respective light spreading lens. The light spreading lens may be formed as a groove in an upper surface of the transparent cover glass. The light spreading lens may have a uniform cross-section along its length. The light spreading lens may be formed as a convex lens on an upper or lower surface of the transparent cover glass.