Multi-Layer Thin Film Stack for IR Sensor Reflection Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing electromagnetic radiation sensor micro-devices struggle to effectively suppress short IR-wavelengths below 8µm, leading to blurred or falsified IR-pictures in temperature measurements due to the lack of filtering ability, which is critical for IR-sensors, and additional filter windows increase costs and radiation absorption.
Innovation Solution
Integration of a multi-layer thin film stack as a reflection reducing coating and filter, specifically a Ge-ZnS or Ge-ZnSe stack, which acts as a low-pass filter to block wavelengths below 5-8µm, improving radiation transmission while reducing reflection and absorption losses, and can be deposited on both sides of the substrate and cover wafers to enhance optical quality and reduce device bending.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a single layer thin film or simple surface texture is used for reducing reflection, then reflection is reduced, but filtering ability for short IR-wavelengths is not provided
Solution Approach 1:
The patent applies a multi-layer thin film stack consisting of alternating layers of germanium (Ge) and zinc sulfide (ZnS) or zinc selenide (ZnSe). This composite structure combines materials with different optical properties to achieve both anti-reflective functionality and wavelength-selective filtering. The specific layer thicknesses and material combinations create destructive interference for short wavelengths while maintaining transmission for 8-12µm IR radiation.
Solution Approach 2:
The optical coating is segmented into multiple discrete layers rather than using a single homogeneous layer. Each layer has specific thickness (e.g., Ge layers at 200-500nm, ZnS/ZnSe layers at 100-300nm) that contributes to the overall filtering and anti-reflective performance. This segmentation allows independent optimization of each layer's thickness and material properties to achieve the desired spectral response.
2Object-affected harmful factors
If an additional filter window is provided in the optical path, then filtering of short IR-wavelengths is achieved, but costs increase and IR-radiation absorption increases
Solution Approach 1:
The patent merges the filtering function with the existing cover wafer structure by depositing the multi-layer thin film stack directly onto it. This integration eliminates the need for a separate filter window component, reducing device complexity and the number of optical interfaces. The combined structure performs both protective covering and wavelength-selective filtering functions simultaneously.
Solution Approach 2:
The cover wafer is given multiple functions: it serves as both the protective enclosure and the wavelength-selective filter. The multi-layer thin film stack on the cover wafer provides both anti-reflective properties and short-wavelength filtering, making the cover wafer a multi-functional component that reduces overall device complexity.
3Manufacturing precision
If multi-layer thin film stack is deposited on both sides of wafers, then optical quality is enhanced and device bending is reduced, but manufacturing complexity increases
Solution Approach 1:
The multi-layer thin film stack is deposited on the wafers before the final device assembly and wafer bonding steps. This preliminary deposition allows the optical coatings to be applied to flat, accessible surfaces, simplifying the deposition process. After device fabrication and bonding, the wafers are singulated, and the pre-deposited coatings remain intact on the final device structures.
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 significantly enhances the transmission of IR-radiation in the 8-12µm range while suppressing short wavelengths, improving the optical quality and reducing radiation losses, allowing for miniaturized and cost-effective production of electromagnetic radiation sensor micro-devices with enhanced filtering and anti-reflective properties.
Implementation Method 1
The first and second layer are of such layer thickness, that for a certain range of wavelength of electromagnetic radiation, which range of wavelength has to be filtered or blocked, there occurs destructive interference.
Implementation Method 2
The first layer has a first refractive index and the second layer has a second refractive index different from the first refractive index of said first layer.
Implementation Method 3
there occurs destructive interference at the boundary interfaces between adjacent first layers and second layers
Implementation Method 4
acts as a low-pass filter to block wavelengths below 5-8µm, improving radiation transmission while reducing reflection and absorption losses
Data Source
Figure 1
Figure 2
Figure 3
AI summary
The invention refers to an electromagnetic radiation sensor micro device for detecting electromagnetic radiation, which device comprises a substrate and a cover at least in part consisting of an electromagnetic radiation transparent material, and comprising a reflection reducing coating and providing a hermetic sealed cavity and an electromagnetic radiation detecting unit arranged within the cavity. The reflection reducing coating is arranged in form of a multi-layer thin film stack, which comprises a first layer and a second layer arranged one upon the other. The first layer has a first refractive index and the second layer has a second refractive index different from the one of said first layer. First and second layer are of such layer thickness that for a certain wavelength there is destructive interference. The invention also refers to a wafer element as well as method for manufacturing such a device.