Optical Multilayer Coating with Magnesium Oxyfluoride Interlayer
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Solution Overview
Problem
Existing antireflective coatings using metal fluorides face challenges in controlling reactivity and substrate damage during sputtering, leading to light absorption issues and limited refractive index range, as well as peeling problems with metal fluoride films on metal oxide substrates.
Innovation Solution
A multilayer coating comprising a high-refractive index layer, a magnesium oxyfluoride layer, and a magnesium fluoride layer, where the magnesium oxyfluoride layer has a specific composition (MgxOyFz) with adjusted refractive index and thickness, is stacked on a substrate to suppress light absorption and prevent electronic defects, using a sputtering process that controls the oxygen and fluorine gas ratios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a metal fluoride film is formed by sputtering process, then the antireflective coating can be deposited, but light absorption occurs at the base interface due to substrate reduction
Solution Approach 1:
A metal oxide film is introduced as an intermediary layer between the glass substrate and the metal fluoride film. This intermediate layer prevents direct contact between fluorine atoms and the substrate, avoiding reduction reactions and electronic defect formation that cause light absorption. The metal oxide film acts as a protective barrier while maintaining the antireflective functionality of the overall coating structure.
Solution Approach 2:
The metal oxide film is formed on the substrate before depositing the metal fluoride film. This preliminary action prepares the substrate surface by creating a stable oxide layer that resists reduction by subsequent fluorine exposure, preventing the formation of altered layers with electronic defects before they can occur.
2Object-affected harmful factors
If metal oxide thin film is used between substrate and metal fluoride film, then light absorption is suppressed, but refractive index range is limited
Solution Approach 1:
The patent employs composite material structures by combining metal oxide films with specific compositions (containing SiO2, ZrO2, Al2O3, or TiO2) to achieve a broader range of refractive indices. By varying the composition ratios and types of metal oxides in the intermediate layer, different refractive indices can be obtained while maintaining the protective function against substrate reduction, thus expanding the adaptable refractive index range.
Solution Approach 2:
The refractive index of the metal oxide film is controlled by changing compositional parameters (ratios of different metal oxides) and deposition parameters (thickness, density). By adjusting these parameters, the refractive index can be tuned within a broader range while maintaining the film's protective function against fluorine-induced substrate reduction.
3Object-affected harmful factors
If metal oxide thin film containing SiO2 is formed, then light absorption is suppressed, but metal fluoride film peeling occurs
Solution Approach 1:
The patent applies local quality by using different metal oxide compositions in different regions or layers of the intermediate film structure. Specifically, it employs metal oxides with higher adhesion properties (such as TiO2, ZrO2, or Al2O3) in contact with the substrate to ensure strong bonding, while incorporating SiO2 in amounts that provide light absorption suppression without causing peeling. This localized optimization of material properties resolves the adhesion problem while maintaining optical performance.
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 effectively suppresses light absorption at interfaces and expands the refractive index range, preventing peeling and enhancing the antireflective properties of the coating, while maintaining low-cost manufacturing through reactive sputtering without switching target materials.
Implementation Method 1
The sputtering process uses plasma particles such as charged particles and ejects atoms from a material to form a film
Implementation Method 2
fluorine atoms, which have strong oxidizing properties, enter a base interface and therefore the base material of the glass substrate or the metal oxide film is reduced to form an altered layer with electronic defects
Data Source
AI summary
The present invention relates to an optical multilayer coating placed on or above a substrate. The optical multilayer coating includes a high-refractive index layer with a refractive index of 1.76 to 2.7, a magnesium oxyfluoride layer, and a magnesium fluoride layer. The high-refractive index layer, the magnesium oxyfluoride layer, and the magnesium fluoride layer are stacked on or above the substrate in this order and are in contact with each other. The magnesium oxyfluoride layer has a composition represented by the following formula:MgxOyFz (1)where z/x is not less than 0.01 nor greater than 1.45 and z/y is not less than 0.01 nor greater than 3.17.