SPAD Pixel Reflective Structure for Higher Photon Detection Efficiency
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Solution Overview
Problem
Conventional single photon avalanche diodes (SPADs) face limitations in improving photon detection efficiency (PDE) for accurate distance measurement, which is essential for high-accuracy distance measurement systems.
Innovation Solution
A photodetection device with a pixel array unit on a semiconductor substrate, featuring pixel separation walls, photoelectric conversion units, multiplication regions, and reflective portions on both surfaces to enhance light detection efficiency by reflecting light back into the substrate, thereby improving photon detection efficiency (PDE).
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional SPAD structure is used, then device complexity is low, but photon detection efficiency is limited
Solution Approach 1:
The patent introduces reflective portions on both the first surface (front side) and second surface (back side) of the semiconductor substrate, utilizing the third dimension (depth/thickness) to create a dual-surface reflection system. This dimensional expansion allows light to be reflected back into the substrate from both surfaces, increasing the probability of photon detection without significantly complicating the lateral pixel structure.
Solution Approach 2:
The pixel separation wall is segmented to include a reflective portion that protrudes from the pixel separation wall toward the pixel center. This segmentation creates multiple reflection surfaces within the pixel structure, allowing light to be reflected from different locations and angles, thereby increasing the effective detection area and photon detection efficiency.
2Measurement precision
If light is allowed to travel outside the semiconductor substrate, then device structure is simple, but light detection efficiency is reduced
Solution Approach 1:
The patent converts the potentially harmful loss of light traveling outside the substrate into a beneficial effect by introducing reflective portions that bounce this escaped light back into the substrate. The light that would otherwise be lost is now reflected and given another chance to be detected, effectively converting a negative (light loss) into a positive (increased detection opportunity).
Solution Approach 2:
Instead of allowing light to be discarded when it travels outside the substrate, the reflective portions recover this light by reflecting it back into the substrate. This recovery mechanism ensures that light which initially escaped is captured and utilized for detection, improving overall light detection efficiency.
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
The solution significantly enhances photon detection efficiency, allowing for more accurate distance measurements by effectively utilizing light that would otherwise be lost, thereby improving the accuracy and reliability of distance measurement systems.
Implementation Method 1
a photoelectric conversion unit that is provided inside the semiconductor substrate to generate an electric charge by light
Implementation Method 2
electrons (electric charges) generated by photoelectric conversion are multiplied in a PN junction region (avalanche multiplication)
Implementation Method 3
first and second reflective portions that reflect light traveling toward outside the semiconductor substrate into the semiconductor substrate
Data Source
AI summary
A photodetection device is provided which includes a pixel array unit including a plurality of pixels arranged in a matrix on a semiconductor substrate to detect light, in which each of the pixels includes a pixel separation wall that surrounds the pixels and separates the pixels from one another, a photoelectric conversion unit inside the semiconductor substrate to generate an electric charge by light, a multiplication region inside the semiconductor substrate to multiply the electric charge from the photoelectric conversion unit, and first and second reflective portions that reflect light traveling toward outside the semiconductor substrate into the semiconductor substrate, the first reflective portion is provided, on a first surface that receives light of the semiconductor substrate, to protrude from the pixel separation wall toward a pixel center, and the second reflective portion is provided on a second surface of the semiconductor substrate facing the first surface.