Band-pass NIR Filter Thermal Stress Control
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Solution Overview
Problem
Current band-pass near-infrared (NIR) filters face issues with low production yield due to breakage during dicing, refractive index shift at increased temperatures, and high warp and angle shifts, which affect the accuracy and reliability of facial recognition systems.
Innovation Solution
A method for producing band-pass NIR filters involving a glass substrate with a scale factor less than 1500 kPa/K, coated with alternating layers of high and low refractive index materials, where the coating process is optimized to minimize interactive stress through controlled temperature and cooling rates, resulting in reduced refractive index shift and warp at operating temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a narrow band-pass NIR filter is applied to improve signal quality, then the signal to noise ratio is improved, but the production yield decreases due to breakage during dicing
Solution Approach 1:
The patent changes the physical parameters of the glass substrate by controlling the cooling rate from a high temperature state, which modifies the internal stress distribution and thermal properties of the glass. This parameter change allows the glass to better withstand the dicing process while maintaining the narrow bandwidth filter performance, thus resolving the contradiction between signal quality and production yield
Solution Approach 2:
The patent applies a preliminary thermal treatment to the glass substrate by heating it to a high temperature state and then controlling the cooling rate before the filter coating is applied and before dicing. This preliminary action prepares the glass substrate to have reduced internal stress and improved mechanical properties, preventing breakage during subsequent dicing operations while maintaining filter performance
2Temperature
If the NIR filter is used at increased operating temperatures, then the filter can operate in higher temperature environments, but the refractive index of the glass substrate changes leading to a shift of the center wavelength
Solution Approach 1:
The patent changes the thermal history parameters of the glass substrate by controlling the cooling rate from high temperature, which modifies the fictive temperature and thermal expansion characteristics of the glass. This parameter change reduces the refractive index shift at elevated operating temperatures, thereby maintaining center wavelength accuracy while enabling broader temperature operation
Solution Approach 2:
The patent applies a preliminary thermal treatment that creates internal stress distribution in the glass substrate opposing the thermal expansion that would occur at high operating temperatures. This preliminary anti-action compensates for the refractive index changes that would otherwise occur, preventing center wavelength shift while allowing high-temperature operation
3Reliability
If the glass substrate is coated with alternating layers of high and low refractive index material, then the band-pass filter performance is achieved, but the interactive stress between coating and glass increases leading to higher warp and angle shift
Solution Approach 1:
The patent changes the thermal parameters of the glass substrate by controlling the cooling rate from high temperature, which modifies the coefficient of thermal expansion and internal stress state of the glass. This parameter change reduces the mismatch between the glass substrate and the alternating high-low refractive index coating layers, thereby reducing warp and angle shift while maintaining filter performance
Solution Approach 2:
The patent creates local quality differences in the glass substrate by establishing a controlled internal stress distribution through the cooling process. This local quality modification allows different regions of the glass to better accommodate the coating layers, reducing overall warp and angle shift while preserving the band-pass filter functionality
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 method enhances production yield, reduces refractive index shift, and minimizes warp and angle shifts, leading to improved signal quality and reliability in facial recognition systems.
Implementation Method 1
α is the coefficient of thermal expansion (CTE) in the range of 20° C. to 300° C.
Implementation Method 2
the glass has a length L0,GL-LTS,GL when reaching T0, wherein LTS,GL accounts for length reduction due to a decrease of fictive temperature
Implementation Method 3
Depositing a band-pass NIR coating comprising alternating layers of high refractive index material and low refractive index material on at least one side of the glass substrate
Implementation Method 4
the maximum internal stress of the glass substrate at operating temperature TOT is smaller than 500 MPa
Data Source
AI summary
A band-pass near-infrared (NIR) filter has a glass substrate and at least one coating. The glass substrate has a scale factor that is smaller than 1500 kPa/K. The maximum internal stress of the glass substrate at an operating temperature TOT is smaller than 300 MPa. A method of production of such a band-pass NIR filter includes depositing a band-pass NIR coating that has alternating layers of high refractive index material and low refractive index material on at least one side of the glass substrate to form a coated glass substrate. Such a band-pass NIR filter can be used in an infrared sensor for object recognition.