Infrared Detector Hermetic Housing with Low-Refractive Index Optical Structure
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Solution Overview
Problem
The monolithic manufacturing technique for hermetic housing in infrared detectors faces challenges in adjusting transmittance to achieve higher values, particularly in the 8-14µm wavelength range, due to complex constraints involving optical thickness, refractive indices, and mechanical strength, leading to suboptimal performance and sensitivity issues.
Innovation Solution
The method involves producing a hermetic housing with a first optical structure having an equivalent refractive index less than or equal to 2.6, using materials like amorphous silicon or its alloys, and incorporating a periodic network of depressions to adjust the optical thickness and refractive index, ensuring high transmittance and mechanical integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a hermetic housing is manufactured using monolithic technique with conventional optical structures, then mechanical strength is ensured, but transmittance in the 8-14µm range is suboptimal
Solution Approach 1:
The patent applies parameter changes by precisely controlling the optical thickness of the first optical structure to be greater than or equal to λ10/10 and adjusting its equivalent refractive index to be less than or equal to 2.6. These parameter optimizations enable the optical structure to achieve high transmittance in the 8-14µm wavelength range while maintaining mechanical integrity through the periodic network of depressions.
Solution Approach 2:
The patent employs composite materials by using amorphous silicon or its alloys for the first optical structure, which provides both the required optical properties (refractive index ≤ 2.6) and mechanical strength. The combination of material composition and structural design (periodic depressions) creates a composite solution that simultaneously achieves high transmittance and structural reliability.
2Reliability
If the optical thickness of the first optical structure is increased to improve transmittance, then absorption by the bolometric membrane increases, but the mechanical strength of the cover may be compromised
Solution Approach 1:
The patent introduces a periodic network of depressions in the first optical structure, creating a porous-like structure that reduces the equivalent refractive index to ≤ 2.6. This structural modification allows the optical thickness to be increased (≥ λ10/10) for improved absorption while the periodic depressions maintain mechanical strength by distributing stress and preventing catastrophic failure modes.
3Reliability
If conventional materials with high refractive indices are used in the optical structure, then mechanical integrity is maintained, but transmittance in the target wavelength range is reduced
Solution Approach 1:
The patent specifies that the first optical structure must have an equivalent refractive index ≤ 2.6, which is a significant reduction from conventional high-refractive-index materials. This parameter change is achieved through using amorphous silicon or its alloys with controlled composition, enabling high transmittance in the 8-14µm range while remaining compatible with standard microelectronic manufacturing processes.
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 enhances the average transmittance in the 8-14µm range, achieving absorption greater than 90% for the bolometric membrane, thereby improving the detector's sensitivity and performance.
Implementation Method 1
the equivalent refractive index at the wavelength λ10 of the first optical structure is less than or equal to 2.6
Implementation Method 2
the optical thickness of the first optical structure is greater than or equal to λ10 / 10
Implementation Method 3
absorption greater than 90% for the bolometric membrane
Implementation Method 4
bolometric detectors operating at room temperature
Data Source
Figure 1~2A
Figure 2B~2E
Figure 2F~2I
AI summary
A method for manufacturing a detector capable of detecting a wavelength range [λ8; λ14] centered on a wavelength λ10, the detector comprising a detection device capable of detecting said range [λ8; λ14] and a hermetically sealed housing under predetermined pressure in which said device is housed, said housing being formed of a substrate, side walls integral with the substrate and a top cover integral with the side walls and comprising a portion adjacent to the device which is transparent in said range [λ8; λ14], the method comprising: - the fabrication of said device on the substrate, said fabrication comprising the deposition of a sacrificial layer completely immersing said device; - the fabrication of the top cover on the sacrificial layer, said top cover being made up of a stack of first, second and third optical structures transparent in said range [λ8;λ14], the second and third optical structures having refractive indices equivalent to the wavelength λ10 respectively greater than or equal to 3.4 and less than or equal to 2.3; - following the fabrication of a portion of the hood comprising at least the first optical structure, the fabrication of an access vent to the sacrificial layer through said portion of the hood, followed by the application, through the vent, of an etch to completely remove the sacrificial layer. - the optical thickness of the first optical structure is greater than or equal to λ10/10; - the equivalent refractive index neq1 at the wavelength λ10 of the first optical structure is less than or equal to 2.6; and - the face of the first optical structure formed on the sacrificial layer is inert to the etch implemented to remove the sacrificial layer.