UV Reference Photodiode with Selective UVC Noise Subtraction
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Solution Overview
Problem
Conventional photodiodes face challenges in sensitivity and durability, particularly in the ultraviolet range, with noise levels in output signals being difficult to manage due to stray light and dark current issues, especially in the UVC range where signal intensity is low.
Innovation Solution
A method of forming a photodiode with specific doping steps and an effective medium to increase UV sensitivity, combined with a reference photodiode configuration using a silicon nitride passivation layer to selectively absorb UVC light, allowing for accurate detection of low-intensity UV signals by subtracting reference current from primary photodiode current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a reference photodiode is used to subtract dark current, then noise level is reduced, but sensitivity in the UVC range deteriorates due to absorption by passivation layers
Solution Approach 1:
The patent changes the optical parameter (thickness) of the silicon nitride passivation layer to be between 10 nm and 250 nm. This specific thickness range allows the layer to be transparent to UVC light wavelengths of 200-275 nm while still providing effective dark current subtraction capability, thus resolving the contradiction between noise reduction and sensitivity maintenance
Solution Approach 2:
The patent uses a composite structure combining silicon nitride passivation layer with specific thickness control to achieve both dark current rejection and UVC transparency. The composite approach of material selection and dimensional control creates a solution that simultaneously addresses both requirements
2Measurement precision
If photodiode area is increased to improve sensitivity, then detection capability is enhanced, but chip area requirements increase
Solution Approach 1:
By optimizing the passivation layer thickness to 10-250 nm, the patent enables smaller photodiode areas to maintain high UVC sensitivity. The optimized parameter allows reduced chip area while preserving detection capability because the thin passivation layer no longer blocks UVC light
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 enhances sensitivity in the UVC range, reduces noise, and maintains performance under UV light stress, enabling accurate detection of weak signals with improved signal-to-noise ratio and reduced chip area requirements.
Implementation Method 1
a silicon nitride passivation layer to absorb light in a first wavelength range in the UV spectrum
Implementation Method 2
Photodiodes are used in a wide range of applications for detecting and measuring electromagnetic radiation
Data Source
AI summary
An optical UV sensor comprises:a first photodiode sensitive to light in a first wavelength range and to light in a second wavelength range in the UV spectrum, wherein the second wavelength range comprises longer wavelengths than the first wavelength range, and wherein the first photodiode is configured to output a first signal in response to incident light;a second photodiode sensitive to light in the second wavelength range and comprising an absorption layer having an optical thickness in the range of 10 nm to 250 nm to absorb light in the first wavelength range, while being substantially transparent to light in the second wavelength range, wherein the second photodiode is configured to output a second signal in response to incident light;wherein the optical sensor is configured to output a difference between the first signal and the second signal.