Dual Photodiode UV Sensor With Visible-Light Noise Rejection
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Solution Overview
Problem
Silicon-based photodiodes have higher responsivity to visible light than ultraviolet (UV) light, leading to noise interference from stray light at longer wavelengths, making it difficult to accurately detect low-intensity UV light, particularly in the range of 200 to 275 nm.
Innovation Solution
A method of forming a photodiode with a specific doping sequence and effective medium to increase UV sensitivity, combined with a reference photodiode insensitive to UV light in this range, allowing for accurate intensity measurement by subtracting the reference photodiode's current from the primary photodiode's current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a silicon-based photodiode is used for detecting UV light, then the sensitivity range is wide including visible and UV light, but the responsivity is higher for visible light than UV light causing noise from stray light
Solution Approach 1:
The photodiode structure is segmented into multiple functional layers: a UV-sensitive photodiode layer and a visible light blocking layer. This segmentation allows the device to selectively detect UV light while blocking visible light that would create noise, resolving the contradiction between wide spectral response and UV-specific sensitivity.
Solution Approach 2:
A visible light blocking layer is introduced as an intermediary between the incident light and the photodiode active region. This intermediary layer selectively transmits UV light while absorbing visible light, enabling the photodiode to detect UV signals without interference from visible stray light noise.
2Measurement precision
If the responsivity to visible light is high, then the photodiode detects a wide range of light, but the signal from UV light is obscured by noise from stray light at longer wavelengths
Solution Approach 1:
The harmful visible light component is extracted and removed from the light path before reaching the photodiode active region. The visible light blocking layer selectively absorbs visible wavelengths while allowing UV wavelengths to pass through, thereby extracting the noise source and preserving the UV signal integrity for accurate measurement.
Solution Approach 2:
Different regions of the photodiode structure are assigned different optical properties: the UV-sensitive region maintains high responsivity to UV light, while the visible light blocking layer introduces selective absorption for visible wavelengths. This local differentiation of optical properties enables precise UV detection by suppressing visible light noise in specific structural zones.
3Reliability
If a reference device is used to subtract dark current, then the noise level is improved, but the sensitivity and durability need further improvement
Solution Approach 1:
The visible light blocking layer is incorporated into the photodiode structure during manufacturing, performing the light filtering function in advance before light detection occurs. This preliminary structural arrangement ensures that only UV light reaches the active region, eliminating the need for complex post-processing noise correction and improving both sensitivity and long-term reliability under UV exposure.
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
Enhances UV sensitivity and reduces noise interference, enabling accurate detection of low-intensity UV light in the 200 to 275 nm range with improved durability against UV light exposure.
Implementation Method 1
Photodiodes are used in a wide range of applications for detecting and measuring electromagnetic radiation
Implementation Method 2
performing a third doping by injecting dopants at a first angle relative to the surface of the wafer in order to increase a doping concentration of the second type of doping at along the sides of the trenches in the second well
Data Source
AI summary
An optical sensor comprises a first and a second photodiode. Each photodiode comprises a respective light sensitive area. The second photodiode further comprises a wavelength-selective absorption layer arranged to selectively attenuate incident light before the light enters the light sensitive area of the second photodiode. The wavelength-selective absorption layer characterized by a low optical absorption in a wavelength range of 300 to 1100 nm and a high optical absorption in a wavelength range of 200 to 275 nm. The photodiodes are configured to generate respective electrical currents in response to incident light, and the optical sensor is configured to determine a light level based on a discrepancy between the electrical current generated by the first photodiode and the electrical current generated by the second photodiode.