Shallow Junction Photodiode Ruggedness via Deep P-Zone
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Solution Overview
Problem
Conventional shallow junction photodiodes are prone to junction degradation and yield loss during assembly, especially when scintillator crystals are mounted, due to their shallow P+N junction, which affects their ruggedness and reliability in applications like CT and X-ray scanning.
Innovation Solution
A photodiode design with a deep, lightly doped P-zone underneath the shallow P+ layer, moving the PN junction deeper and increasing the integrated total boron dose, resulting in improved ruggedness and stability, and reducing the likelihood of degradation during assembly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a shallow P+N junction is used in conventional photodiodes, then the photodiode can detect short wavelength light effectively, but the junction is prone to degradation and yield loss during assembly
Solution Approach 1:
The patent changes the depth parameter of the P+N junction from shallow (conventional) to deep (invention), moving the junction deeper into the substrate to improve ruggedness and reduce degradation during assembly while maintaining short wavelength detection capability
Solution Approach 2:
The patent introduces a vertical depth dimension consideration by creating a deep P+N junction that extends significantly into the substrate, adding a new spatial dimension to the traditional shallow junction design to enhance mechanical robustness
2Reliability
If the P+N junction is moved deeper into the substrate, then ruggedness and stability are improved, but detection efficiency for short wavelength light may be reduced
Solution Approach 1:
The patent applies local quality by creating a deep P+N junction specifically in regions where mechanical robustness is needed, while maintaining optimized doping profiles and junction characteristics in light-sensitive areas to preserve detection efficiency
3Productivity
If a shallow P+N junction is used, then fabrication is simpler and faster, but yield is reduced due to degradation during assembly
Solution Approach 1:
The patent performs preliminary action by pre-positioning the P+N junction at a deeper, more robust location during the fabrication process, which prevents degradation issues before assembly occurs, thereby improving yield without significantly impacting fabrication speed
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 improved photodiode exhibits enhanced ruggedness, stability, and performance characteristics, including lower dark current and improved signal-to-noise ratio, while reducing fabrication costs and increasing yield.
Implementation Method 1
Silicon photodiodes are sensitive to light in the wide spectral range, extending from deep ultraviolet through visible to near infrared
Data Source
AI summary
The present invention is a photodiode or photodiode array having improved ruggedness for a shallow junction photodiode which is typically used in the detection of short wavelengths of light. In one embodiment, the photodiode has a relatively deep, lightly-doped P zone underneath a P+ layer. By moving the shallow junction to a deeper junction in a range of 2-5 μm below the photodiode surface, the improved device has improved ruggedness, is less prone to degradation, and has an improved linear current.