Polycrystalline Silicon Infrared Window for High-Sensitivity Sensing
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Solution Overview
Problem
Existing infrared window materials exhibit low transmittance in the wavelength region around 9 μm due to impurity defects, leading to reduced sensitivity in human body sensing, and mid-infrared and near-infrared rays act as stray light, deteriorating the signal-to-noise ratio.
Innovation Solution
A polycrystalline silicon optical member is formed using high-purity trichlorosilane, with a chemical vapor deposition method to achieve high transmittance at 10 μm and low transmittance at 4 μm or less, controlling the average crystal grain size to 5 μm or less to absorb and scatter infrared rays in the mid-infrared and near-infrared regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional infrared window materials are used, then transmittance in the 1.2-6 μm wavelength region is high, but transmittance at 9 μm and around 10.6 μm decreases due to impurity defects
Solution Approach 1:
The invention changes the manufacturing parameters by using a specific CVD process with controlled temperature (900-1200°C) and gas composition (mono-silane and hydrogen) to produce polycrystalline silicon with 9N purity or higher, thereby achieving high transmittance at 9 μm and 10.6 μm while minimizing impurity defects
Solution Approach 2:
The invention uses polycrystalline silicon as a composite material structure that combines the benefits of crystalline order for infrared transmittance with polycrystalline formation ease, achieving both high purity (9N or higher) and excellent transmittance characteristics across multiple wavelength regions including 9 μm and 10.6 μm
2Measurement precision
If polycrystalline silicon with high transmittance at 9 μm is used, then human body sensing capability is improved, but mid-infrared and near-infrared rays act as stray light deteriorating S/N ratio
Solution Approach 1:
The invention applies local quality by creating an anti-reflection coating with specific optical properties that selectively affects different wavelength regions, allowing high transmittance at 10.6 μm while reducing transmittance of mid-infrared and near-infrared rays to minimize stray light
Solution Approach 2:
The invention changes the optical parameters by controlling the refractive index and thickness of the anti-reflection coating to achieve wavelength-selective transmittance, ensuring high transmittance at the target wavelength (10.6 μm) while suppressing transmittance in other regions to reduce stray 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
This configuration enhances the signal-to-noise ratio for human body sensing by minimizing stray light from mid-infrared and near-infrared regions while maintaining high transmittance at 10 μm, allowing for accurate and sensitive human body detection at a lower cost compared to monocrystalline silicon.
Implementation Method 1
A polycrystalline silicon optical member is formed using high-purity trichlorosilane, with a chemical vapor deposition method
Implementation Method 2
absorb and scatter infrared rays in the mid-infrared and near-infrared regions
Implementation Method 3
absorb and scatter infrared rays in the mid-infrared and near-infrared regions
Data Source
AI summary
An optical member made of polycrystalline silicon formed from high-purity trichlorosilane as a raw material, and that absorbs and scatters an infrared ray in a wavelength region of 4 μm or less. In the optical member, a ratio A/B between a transmittance A of an infrared ray having a wavelength of 4 μm and a transmittance B of an infrared ray having a wavelength of 10 μm is 0.9 or less, and an average crystal grain size of the polycrystalline silicon is 5 μm or less. This polycrystalline silicon is produced by hydrogen reducing SiHCI3 by heating a base material to 800 to 900° C. using a chemical vapor deposition method. In this way, an infrared ray transmissive optical member, a manufacturing method thereof, an optical device, an infrared detector, and an optical apparatus capable of sensing a human body with high sensitivity and accuracy are realized.