Avalanche Photodiode Pixel Structure for Ambient-Light Distance Sensing
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Solution Overview
Problem
The distance measurement accuracy of existing distance measuring image sensors decreases when the amount of reflected light from an object is small, especially for distant objects, due to the interference of ambient light.
Innovation Solution
An avalanche photodiode sensor is designed with a first semiconductor substrate having a matrix arrangement of photoelectric conversion portions and element separation portions, along with concave-convex portions on the opposing surface, and a second semiconductor substrate with a reading circuit connected to each photoelectric conversion portion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional distance measuring image sensor is used, then distance measurement can be performed, but the measurement precision deteriorates when the amount of reflected light is small due to ambient light interference
Solution Approach 1:
The sensor divides the photoelectric conversion area into multiple pixels with element separation portions between them. This segmentation prevents ambient light from affecting all pixels uniformly and allows selective reading of photons from the direction of interest, improving distance measurement precision in the presence of ambient light
Solution Approach 2:
The element separation portions are strategically placed only between adjacent pixels where light leakage occurs, rather than uniformly across the entire sensor. This localized approach reduces ambient light interference at critical interfaces while maintaining photoelectric conversion efficiency in the active regions
2Quantity of substance
If the amount of reflected light is small (distant objects), then the reflected light becomes buried in ambient light, but increasing the sensor area to capture more light may increase ambient light interference
Solution Approach 1:
By dividing the sensor into multiple pixels with separation portions, the sensor can capture more photons from the direction of interest across multiple pixels while the separation portions prevent ambient light from uniformly affecting all pixels, maintaining measurement accuracy even with small reflected light amounts
Solution Approach 2:
The element separation portions extend in the depth direction (from light incident surface to opposite surface), creating a three-dimensional barrier against light leakage. This vertical dimension adds effective path length for blocking ambient light while maintaining a compact planar footprint
3Measurement precision
If element separation portions are added to prevent light leakage, then measurement precision improves, but device complexity increases
Solution Approach 1:
The element separation portions create a porous-like structure with isolated regions between pixels. This porous arrangement effectively blocks light leakage paths while maintaining a relatively simple overall sensor structure that can be manufactured using standard semiconductor fabrication processes
Solution Approach 2:
The sensor is segmented into repeating units of photoelectric conversion portions and element separation portions. This modular segmentation allows the complex function of light isolation to be achieved through simple, repetitive structural elements that are easy to manufacture
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 configuration enhances the distance measurement precision by improving the light incidence efficiency and reducing light leakage between pixels, thereby increasing the quantum efficiency of the photoelectric conversion portions.
Implementation Method 1
a pixel array formed by arranging a plurality of single photon avalanche diode (SPAD) pixels in a plane... In a SPAD pixel, avalanche amplification occurs if a photon enters its PN junction region
Implementation Method 2
In a SPAD pixel, avalanche amplification occurs if a photon enters its PN junction region of a high electric field while a voltage much higher than a breakdown voltage is being applied
Data Source
AI summary
An avalanche photodiode sensor according to an embodiment includes a first semiconductor substrate and a second semiconductor substrate bonded to a first surface of the first semiconductor substrate, wherein the first semiconductor substrate includes a plurality of photoelectric conversion portions arranged in a matrix and an element separation portion for element-separating the plurality of photoelectric conversion portions from each other, the plurality of photoelectric conversion portions include a first photoelectric conversion portion, the element separation portion has a first element separation region and a second element separation region, the first photoelectric conversion portion is arranged between the first element separation region and the second element separation region, the first semiconductor substrate further includes a plurality of concave-convex portions arranged on a second surface opposite to the first surface and arranged between the first element separation region and the second element separation region, and the second semiconductor substrate includes a reading circuit connected to each of the photoelectric conversion portions.