Stress Isolated Microbolometer Detector Element Design
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Solution Overview
Problem
Microbolometer detectors face stress-induced twisting and tilting due to material properties, leading to thermal shorts and malfunctions in arrays, as stress is transmitted to support structures, causing physical contact between detector elements and the substrate.
Innovation Solution
The design incorporates a stress-isolated detector element with a platform structure having a central beam and split thermistor configuration, where the support structure is interposed between the detector element and substrate, reducing stress transmission to the support arms, thereby minimizing deformation and thermal shorts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a suspended platform structure is used for the detector element, then thermal isolation from the substrate is achieved, but stress is transmitted to the support structure causing twisting and tilting
Solution Approach 1:
The detector element is segmented into a platform structure with a central beam and peripheral region, where the beam provides structural support and the peripheral region houses the thermistor. This segmentation allows the stress-bearing functions and thermal isolation functions to be separated, with the beam carrying stress away from the support structure while maintaining thermal isolation.
Solution Approach 2:
The central beam acts as an intermediary element between the support structure and the thermistor-containing peripheral region. It mediates the stress transmission by providing a rigid structural framework that prevents stress from being transmitted to the support arms, while still allowing the platform to be thermally isolated from the substrate.
2Temperature
If the detector element is suspended by support arms, then thermal isolation is maintained, but stress causes physical contact between detector elements and substrate
Solution Approach 1:
The platform structure is divided into a central beam region and a peripheral region with the thermistor. This segmentation creates a rigid central support that prevents the entire platform from deforming under stress, thereby maintaining the clearance between the detector element and substrate while preserving thermal isolation through the support arms.
Solution Approach 2:
The rigid central beam structure provides beforehand structural reinforcement that prevents stress-induced deformation before it can cause physical contact between the detector element and substrate. This preemptive structural support cushioning ensures the detector element maintains its position and avoids malfunction.
3Measurement precision
If material properties cause stress in the detector element, then the thermistor responds to temperature changes, but stress transmission causes twisting and tilting
Solution Approach 1:
The detector element is segmented into a rigid central beam and a peripheral region containing the thermistor. This segmentation isolates the thermistor from mechanical stress while maintaining its temperature sensing capability, as the beam provides structural stability without interfering with the thermistor's electrical properties and temperature response.
Solution Approach 2:
Different regions of the platform structure are given different mechanical properties: the central beam is designed with high rigidity to resist stress and maintain shape, while the peripheral region is optimized for thermal sensing. This local differentiation of structural quality allows the thermistor to accurately sense temperature changes without being affected by stress-induced deformation.
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 configuration effectively reduces stress on support structures, preventing twisting and tilting, which in turn decreases thermal shorting and enhances the reliability and performance of microbolometer focal plane arrays by isolating support arms from stress.
Implementation Method 1
The suspended platform structure may be provided with a thermistor whose electrical resistivity varies in response to temperature variations caused by the absorbed radiation
Implementation Method 2
The platform structure is generally held above and thermally insulated from a substrate by a support structure
Data Source
Figure 1~2
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Figure 5~6
AI summary
A detector element for a microbolometer detector includes a platform structure (86) spaced apart from a substrate (76). The platform structure has a peripheral region (90) surrounding a central region (88). First and second contacts (100, 102) are located at the peripheral region (90) proximate opposing first and third edges of the peripheral region. A stiff beam structure (104) extends across the central region between the first and second contacts (100, 102), and at least one sensor is located at the peripheral region (90) proximate at least one of second and fourth edges of the peripheral region. An optically absorptive material structure (114) of a grid pattern of first and second material portions may be located at the central region. First material portions perpendicular to the beam structure may connect to the beam structure and to inner edges of the peripheral region, and none of the second material portions extend continuously between and couples to opposing inner edges of the peripheral region.