Carbon Nanotube Bolometer Alignment for High TCR and Low Resistance
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Solution Overview
Problem
Existing bolometers using carbon nanotube thin films suffer from low Temperature Coefficient of Resistance (TCR) at room temperature and high resistance, limiting the sensitivity and performance of infrared sensors.
Innovation Solution
A bolometer with a carbon nanotube layer comprising 90% or more semiconducting carbon nanotubes, aligned to satisfy a specific alignment ratio (fx/fy≥2) achieved through a method involving a carbon nanotube dispersion liquid, substrates, and controlled evaporation and alignment processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If typical single-walled carbon nanotubes are used in a bolometer unit, then the manufacturing cost is reduced and chemical stability is improved, but the TCR value is low due to the presence of metallic carbon nanotubes mixed with semiconducting carbon nanotubes
Solution Approach 1:
The patent extracts and removes metallic carbon nanotubes from the mixed carbon nanotube population, retaining only semiconducting carbon nanotubes. This is achieved through selective dissolution methods where metallic nanotubes are removed while semiconducting nanotubes are preserved, resulting in a pure semiconducting carbon nanotube layer with high TCR value (-2.6%/K or higher) while maintaining ease of manufacture through thin film processes
Solution Approach 2:
The patent changes the compositional parameter of the carbon nanotube layer from a mixed state (2:1 ratio of semiconducting to metallic) to a pure semiconducting state (90% or more semiconducting carbon nanotubes). This parameter change fundamentally improves the TCR value while the manufacturing process remains relatively simple, resolving the contradiction between ease of manufacture and reliability
2Reliability
If semiconducting single-walled carbon nanotubes are separated and used in the bolometer section, then the TCR value is enhanced to -2.6%/K, but the bolometer resistance remains high which limits sensitivity
Solution Approach 1:
The patent applies local quality by creating highly aligned carbon nanotube structures where the orientation and arrangement of nanotubes are optimized in specific regions. The carbon nanotubes are arranged with their axes substantially parallel to each other, creating localized pathways that reduce resistance while maintaining the high TCR property of semiconducting nanotubes throughout the bolometer section
Solution Approach 2:
The patent creates a composite structure combining semiconducting carbon nanotubes with supporting matrix materials (such as dielectric layers and electrode structures). This composite approach allows the carbon nanotube layer to achieve both high TCR and reduced resistance through the synergistic effects of the aligned nanotube network and the supporting material structure
3Reliability
If carbon nanotubes are aligned to achieve high TCR and low resistance, then the sensitivity is enhanced, but the manufacturing process becomes more complex
Solution Approach 1:
The patent applies preliminary action by pre-aligning carbon nanotubes during the thin film deposition process before subsequent processing steps. The carbon nanotubes are deposited and aligned in their final configuration during the fabrication process, eliminating the need for complex post-alignment operations and reducing overall manufacturing complexity while achieving high sensitivity
Solution Approach 2:
The patent employs self-service by utilizing the inherent properties of carbon nanotubes and the deposition environment to achieve automatic alignment during the fabrication process. The carbon nanotubes self-organize into aligned structures through their deposition from solution or vapor, eliminating the need for external alignment mechanisms and simplifying the manufacturing process while achieving high sensitivity
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 resulting bolometer exhibits a high TCR value and low resistance, enhancing the sensitivity and performance of infrared sensors while being manufactured at a lower cost.
Implementation Method 1
providing a liquid film of the carbon nanotube dispersion liquid on the lower substrate; sandwiching the liquid film by the lower substrate and the upper substrate to form an edge of the liquid film along the first side; and moving the upper substrate and/or the lower substrate so that a relative moving direction of the upper substrate with respect to the lower substrate is perpendicular to the first side and toward the inside of the plane of the upper substrate
Data Source
AI summary
An object of the present invention is to provide a bolometer having a high TCR value and a low resistance, and a method for manufacturing the infrared sensor. One aspect of the present embodiment relates to a bolometer comprising: a substrate; a first electrode on the substrate; a second electrode spaced from the first electrode on the substrate; and a carbon nanotube layer electrically connected to the first electrode and the second electrode, wherein the carbon nanotube layer comprises 90% by mass or more of semiconducting carbon nanotubes based on the total amount of carbon nanotubes, and the carbon nanotube layer has an alignment satisfying: fx/fy≥2 where an integrated value f of amplitudes of frequencies from −1 μm−1 to +1 μm−1 in one direction from the center is calculated in an image obtained by performing two-dimensional fast Fourier transform processing on an SEM image of the carbon nanotube layer, and an integrated value for a direction x in which the integrated value f becomes maximum is defined as fx and an integrated value for a direction y perpendicular to the direction x is defined as fy.