Optical Filter Underlayer Roughness for Silver Film Stability
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Solution Overview
Problem
Existing optical filters using silver or silver alloys as reflective films face issues with aggregation due to temperature changes, leading to deterioration in optical characteristics such as transmittance and reflectance.
Innovation Solution
The optical filter design includes a first and second substrate with underlayers having a maximum height roughness of 7.3 nm or more, on which silver or silver alloy reflective films are formed, preventing aggregation and maintaining optical characteristics even at high temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If silver or silver alloy is formed at the glass substrate, then high reflectance is achieved, but aggregation occurs due to temperature increase leading to deterioration in optical characteristics
Solution Approach 1:
An underlayer is introduced as an intermediary between the glass substrate and the silver/silver alloy reflective film. This underlayer prevents direct contact between the reflective film and substrate, thereby preventing aggregation of the silver particles when temperature increases, while still allowing the reflective film to function effectively.
Solution Approach 2:
The surface roughness of the underlayer is controlled to be within a specific range (0.3 µm to 3.0 µm). By optimizing this physical parameter, the underlayer effectively suppresses aggregation of the silver reflective film while maintaining good optical characteristics and adhesion.
2Reliability
If barrier layer or protective layer is added to prevent metal film deterioration, then reliability is improved, but device complexity increases
Solution Approach 1:
The underlayer performs multiple functions simultaneously: it serves as an adhesion layer between the substrate and reflective film, as a protective barrier preventing aggregation of the silver particles, and as a surface whose controlled roughness optimizes optical performance. This multi-functionality eliminates the need for separate barrier and protective layers.
Solution Approach 2:
The functions of adhesion, protection, and optical optimization are merged into a single underlayer component. By combining these functions, the structure is simplified compared to having separate adhesion layer, barrier layer, and protective layer.
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 design effectively prevents silver alloy aggregation, maintaining high optical characteristics and reducing transmittance changes by less than 15% for wavelengths of 600 nm or more, even under heating conditions.
Implementation Method 1
The first underlayer and the second underlayer have a maximum height roughness of 7.3 nm or more
Implementation Method 2
an underlying step of forming the underlayer on the substrate by sputtering
Data Source
AI summary
An optical filter includes: a first substrate; a second substrate facing the first substrate via a gap; a first underlayer provided on a surface of the first substrate facing the second substrate; a second underlayer provided on a surface of the second substrate facing the first substrate; a first reflective film provided on the first substrate via the first underlayer and made of silver or a silver alloy; and a second reflective film provided on the second substrate via the second underlayer and made of silver or a silver alloy. The first underlayer and the second underlayer have a maximum height roughness of 7.3 nm or more.