APD Pixel Layout With Hole Accumulation for Low Dark Count
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Solution Overview
Problem
Avalanche photodiodes (APDs) face challenges in reducing crosstalk and dark count rate (DCR) due to light emission in high-electric-field regions and dark current generation at interfaces, which affect their sensitivity and detection efficiency.
Innovation Solution
The implementation of a hole accumulation region and an isolation region formed with a silicon oxide film between APDs, which traps electrons and reduces dark current, and the use of a fixed charge film or metallic film to further suppress DCR and enhance photon detection efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a high-electric-field region is formed in the pixel for carrier multiplication, then sensitivity of the SPAD pixel is enhanced, but light emission in this region causes crosstalk to neighboring pixels
Solution Approach 1:
The pixel structure is segmented into multiple regions including a first region with the high-electric-field region for carrier multiplication, a second region as an electron blocking region, and a third region as a hole accumulation region. This segmentation allows the high-electric-field region to maintain sensitivity while the separated electron blocking region prevents electron injection into neighboring pixels, thereby reducing crosstalk.
Solution Approach 2:
The electron blocking region acts as an intermediary structure between the high-electric-field region and the pixel contact. It selectively blocks electrons while allowing holes to pass through to the pixel contact, preventing electron-induced crosstalk to neighboring pixels while maintaining the sensitivity-enhancing high-electric-field region.
2Device complexity
If the pixel structure is simplified, then manufacturing complexity is reduced, but crosstalk and dark count rate cannot be effectively suppressed
Solution Approach 1:
The pixel is segmented into three functional regions: a first region containing the high-electric-field region for carrier multiplication, a second region serving as an electron blocking region, and a third region as a hole accumulation region. This segmentation enables effective suppression of crosstalk and dark count rate while maintaining manufacturing feasibility through standard semiconductor fabrication processes.
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 effectively reduces crosstalk and DCR, enhances photon detection efficiency, and improves the overall performance of APDs by isolating pixels and trapping electrons, thereby improving the detection accuracy and sensitivity.
Implementation Method 1
an isolation region formed with a silicon oxide film between APDs, which traps electrons and reduces dark current
Implementation Method 2
the use of a fixed charge film or metallic film to further suppress DCR and enhance photon detection efficiency
Implementation Method 3
a process in which carriers generated by photoelectric conversion are multiplied in a high-electric-field PN junction region
Implementation Method 4
carriers generated by photoelectric conversion are multiplied in a high-electric-field PN junction region
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
A sensor includes a first substrate including at least a first pixel. The first pixel includes an avalanche photodiode to convert incident light into electric charge and includes an anode (105) and a cathode (101). The cathode is in a well region (103) of the first substrate. The first pixel includes an isolation region (108) that isolates the well region from at least a second pixel that is adjacent to the first pixel. The first pixel includes a hole accumulation region (107a) between the isolation region and the well region. The hole accumulation region is electrically connected to the anode.