TiO2 Bandpass Filter Deposition to Prevent Cavity Layer Cloudiness
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Solution Overview
Problem
Bandpass filters with high refractive index cavity layers, such as TiO2, face cloudiness issues during film formation, leading to deviations in transmission bands and increased scattering, which complicates the reduction of angle dependence and transmittance.
Innovation Solution
A method involving a film formation stop period to lower the substrate temperature during the production of dielectric multilayer films, particularly when forming thick cavity layers with high refractive index materials like TiO2, to suppress crystallization and cloudiness, ensuring improved transmittance and reduced scattering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the cavity layer having the large film thickness is formed using the high refractive index material such as TiO2, then the angle dependence of the bandpass filter is reduced, but the crystallization of TiO2 proceeds and the cavity layer becomes cloudy during film formation
Solution Approach 1:
The film formation process uses periodic action by alternating between film formation periods and stop periods. During the stop periods, the substrate temperature is allowed to decrease, preventing continuous temperature rise that would cause crystallization. This periodic cycling enables formation of thick TiO2 cavity layers without cloudiness while maintaining the high refractive index properties needed for reduced angle dependence.
Solution Approach 2:
The invention changes the temperature parameter dynamically during film formation. By controlling the substrate temperature to decrease during stop periods and maintain appropriate levels during formation periods, the process prevents crystallization of TiO2. This parameter control allows formation of thick cavity layers with film thickness of 150 nm or more while suppressing cloudiness and maintaining optical properties.
2Productivity
If the film formation is performed continuously without stopping, then the productivity is high, but the substrate temperature rises and causes crystallization of TiO2
Solution Approach 1:
The film formation process uses periodic action by alternating between film formation periods and stop periods. During the stop periods, the substrate temperature is allowed to decrease, preventing continuous temperature rise that would cause crystallization. This periodic cycling enables formation of thick TiO2 cavity layers without cloudiness while maintaining the high refractive index properties needed for reduced angle dependence.
Solution Approach 2:
The invention uses skipping by temporarily interrupting the film formation process at critical points. By stopping film formation periodically, the process rushes through the temperature control challenge rather than attempting continuous formation. This allows the substrate temperature to be managed effectively, preventing crystallization while still achieving the required film thickness for low angle dependence.
3Stability of the object's composition
If the cavity layer film thickness is increased to reduce angle dependence, then the transmission band becomes narrower and has sharper rise, but the cloudiness of the cavity layer increases
Solution Approach 1:
The film formation process uses periodic action by alternating between film formation periods and stop periods. During the stop periods, the substrate temperature is allowed to decrease, preventing continuous temperature rise that would cause crystallization. This periodic cycling enables formation of thick TiO2 cavity layers without cloudiness while maintaining the high refractive index properties needed for reduced angle dependence.
Solution Approach 2:
The invention changes the temperature parameter dynamically during film formation. By controlling the substrate temperature to decrease during stop periods and maintain appropriate levels during formation periods, the process prevents crystallization of TiO2. This parameter control allows formation of thick cavity layers with film thickness of 150 nm or more while suppressing cloudiness and maintaining optical properties.
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 approach effectively reduces cloudiness in the cavity layer, enhancing transmittance in the transmission band and minimizing scattering, thereby reducing angle dependence on incident light, even with large film thicknesses.
Implementation Method 1
crystallization of TiO2 proceeds and the cavity layer becomes cloudy during film formation
Data Source
AI summary
This method for producing a bandpass filter is a method for producing a bandpass filter made of a dielectric multilayer film including: a cavity layer made of TiO2; and laminated portions arranged to sandwich the cavity layer, the laminated portion being formed by alternately laminating a first dielectric layer made of a high refractive index material and a second dielectric layer made of a low refractive index material, in which in a film formation step of the dielectric multilayer film, a film formation stop period to lower a temperature of a film formation substrate by temporarily stopping film formation during the film formation step is set.