Microbolometer Quarter-Wave Cavity Absorption Layer Optimization
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Solution Overview
Problem
Microbolometers face challenges in reducing dimensions and cost without compromising sensitivity, as smaller pixel pitches result in lower absorbed power and difficulties in engineering support structures for high thermal resistance absorption layers.
Innovation Solution
A microbolometer design with pixel pitches between 5 and 11 μm and absorption layers having a fill factor of 0.10 to 0.50 and sheet resistance of 16 to 189 ohm/sq, along with a quarter-wave cavity height of 1.5 to 5 μm, which allows for high absorption rates and filtering functionality by optimizing pixel fill factor and sheet resistance ratios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the pixel pitch of a microbolometer is reduced to decrease device dimensions, then the device becomes more compact, but the amount of absorbed power decreases and sensitivity deteriorates
Solution Approach 1:
The patent applies parameter changes by optimizing the sheet resistance of the absorption layer to be between 16 and 189 ohm/sq and the pixel fill factor to be between 0.10 and 0.50. These specific parameter ranges enable the absorption layer to maintain high absorption efficiency even when the pixel pitch is reduced to 5-11 μm, thus resolving the contradiction between compactness and sensitivity.
2Volume of moving object
If the pixel pitch is reduced to decrease device dimensions, then the device becomes more compact, but the engineering difficulty of support structures increases
Solution Approach 1:
The patent resolves this contradiction by specifying that the absorption layer should have a sheet resistance between 16 and 189 ohm/sq. This parameter optimization allows the absorption layer to function effectively with smaller pixel pitches without requiring proportionally more complex support structures, as the electrical properties are tuned to compensate for the reduced physical dimensions.
3Use of energy by moving object
If the pixel fill factor is increased to improve absorption rate, then the absorption rate increases, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent optimizes the pixel fill factor to be between 0.10 and 0.50, which is a moderate range that achieves good absorption without requiring the absorption layer to occupy most of the pixel area. Combined with the sheet resistance optimization, this allows for simpler manufacturing processes compared to designs requiring very high fill factors.
Solution Approach 2:
The patent applies local quality by concentrating the absorption function in a specific layer with optimized electrical properties (sheet resistance 16-189 ohm/sq) rather than requiring the entire pixel area to be filled with absorptive material. This localized optimization achieves high absorption rates while maintaining ease of manufacture.
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 design achieves high absorption rates and compactness while maintaining sensitivity, and provides a filtering function that reduces the need for external optical filters, thereby enhancing the microbolometer's performance and cost-effectiveness.
Implementation Method 1
The membrane comprises an absorption layer that absorbs energy from the IR light hitting the pixel, causing its temperature to rise as a function of the intensity of the IR light
Implementation Method 2
The membrane for example also comprises a thermal layer which has the property that its resistance is modified by this temperature rise, and the pixel can thus be read by detecting the change in resistance of this thermal layer
Data Source
AI summary
The present disclosure relates to a microbolometer comprising an array of pixels, each pixel comprising one or more detection cells, each detection cell comprising an absorption layer (530) forming a quarter-wave cavity (533) having a height (h) of between 1.5 and 5 μm, wherein the pitch of the detection cells in at least one axis in a plane of the pixel array is in the range 2.4 h to 3.6 h.