Multi-Spectral Fabry-Pérot Filter Cavities With Stop-Layer Etching
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Solution Overview
Problem
Existing manufacturing processes for multi-spectral filters using Fabry-Pérot cavities face challenges in achieving precise optical thickness control due to variations in etching speeds and non-uniformity, leading to inconsistent spectral responses and potential failure in detecting radiation within the desired bandwidth.
Innovation Solution
A subtractive method combining layer deposition and selective etching steps, utilizing stop layers and alternating etching of cavity and barrier layers with tailored etching recipes to achieve precision in optical thicknesses comparable to additive methods, allowing for the production of multi-spectral filters with specific cavity thicknesses for each filter element.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If subtractive methods (etching) are used to structure cavities, then manufacturing time is reduced compared to additive methods, but manufacturing precision deteriorates due to etching speed variations and non-uniform etching bottoms
Solution Approach 1:
The patent introduces stop layers as intermediary elements between cavity layers. These stop layers serve as precise thickness reference planes that are not etched away, allowing the cavity thickness to be defined by the distance between two stop layers rather than by etching depth alone. This mediator approach transfers the precision requirement from the etching process to the deposition process, where nanometer-level precision can be achieved.
Solution Approach 2:
The patent changes the control parameter for cavity thickness from etching depth (which has poor precision) to the thickness of deposited stop layers (which has high precision). By controlling the deposition thickness of stop layers with nanometer accuracy and using them as reference planes, the cavity optical thickness can be precisely controlled despite variations in etching speeds.
2Adaptability or versatility
If selective etching steps are used to obtain different cavity thicknesses, then filter elements can be produced with specific thicknesses, but etching speed variations cause spectral response inconsistency
Solution Approach 1:
Stop layers act as intermediary reference planes that are uniformly deposited across all filter elements using the same deposition parameters. This ensures that all cavities have their thickness measured from the same reference level, compensating for variations in etching speeds between different structuring steps and ensuring consistent spectral responses.
Solution Approach 2:
The stop layers are deposited in advance before the final cavity thickness adjustment etching. This preliminary deposition establishes precise reference planes that define the target thickness, allowing subsequent etching steps to be performed with relaxed precision requirements while still achieving the desired final dimensions.
3Manufacturing precision
If etching steps are used to reduce cavity thickness, then filter cavities can be structured to desired thicknesses, but non-flat etching bottoms cause layer thickness non-uniformity
Solution Approach 1:
The stop layers serve as intermediary reference planes with perfectly flat tops (deposited by conformal deposition). Subsequent cavity layers are deposited on these flat reference planes, ensuring uniform layer thickness across the entire filter array. The non-flat etching bottoms are compensated for by using the stop layer as a new reference plane rather than etching directly to the final thickness.
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 enables precise control of optical thicknesses, ensuring accurate spectral positioning of filter passbands, improving spectral selectivity and reducing the risk of spectral shifting, while also offering significant time savings compared to traditional additive methods.
Implementation Method 1
The selective etching steps implement etching techniques (for example by chemical or ionic means)
Implementation Method 2
The selective etching steps implement etching techniques (for example by chemical or ionic means)
Implementation Method 3
A Fabry-Pérot filter consists of an optical cavity formed by an interstitial medium of transparent material sandwiched between two reflectors (or mirrors). When a light wave propagates in this structure, it makes several round trips in the interstitial medium due to its reflection at the reflectors.
Implementation Method 4
Additive methods rely on vacuum thin-film deposition techniques
Implementation Method 5
Additive methods rely on vacuum thin-film deposition techniques
Data Source
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AI summary
The present invention relates to a method for manufacturing a multi-spectral filter comprising a plurality of filtering elements, each filtering element being adapted to transmit a spectral electromagnetic radiation band from among a plurality of spectral bands, characterised in that the method comprises the following steps: - depositing a first common reflector for the plurality of filtering elements onto a substrate; - depositing, onto the first reflector, a first cavity stack comprising at least N cavity layers and N-1 barrier layers deposited in an alternating manner, the upper layer being a cavity layer; - selectively etching a number M of cavity layers in a plurality of zones each corresponding to a filtering element, where M varies from 0 to N-1 from one zone to the next; and - selectively etching barrier layers located between the etched cavity layers, and so that each filtering element comprises N-M cavity layers and N-M-1 non-etched barrier layers, and in that the cavity layers and the barrier layers are produced from different and optically transparent materials.