2021 Fiscal Year Annual Research Report
Novel terahertz NEMS bolometers by using two-dimensional nanomaterials
| Project/Area Number |
19K15023
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| Research Institution | Tokyo University of Agriculture and Technology |
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Principal Investigator |
張 亜 東京農工大学, 工学(系)研究科(研究院), 准教授 (80779637)
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| Project Period (FY) |
2019-04-01 – 2022-03-31
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| Keywords | terahertz / thermal sensor / graphene / NEMS |
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| Outline of Annual Research Achievements |
This research aims at developing fast and sensitive bolometers with 2D materials such as graphene. In the research of this year, we fabricated suspended graphene bolometer with asymmetric metal electrodes. Monolayer and multilayer (6~8 layers) CVD grown graphene films were transferred to silicon(Si)/SiO2 substrates, and patterned into small dashes by oxygen plasma etching. Electrodes of two types of metals (Au and Al) were deposited to contact the graphene dashes, which have different working functions. Vapor HF etching was performed to remove the SiO2 under the graphene to form the suspended graphene beam structure.
To estimate the optical responsivity, we illuminated the bolometer with a 400 nm laser to heat up the graphene layer. The hot electrons were driven by the field gradient formed by the asymmetric electrodes, and gave an open-circuit voltage among the Au-Al electrodes. We have found that, at weak illumination (<2 mW), the output voltage increased linearly with input optical power, and the responsivity was about ~90 V/W. However, when the power became large, the output voltage saturated at about 200 mV, which is probably limited by the potential difference of the laterally separated Au-Al electrodes. When the light chopping frequency increased to ~1 kHz, we did not see any drop in the output voltage. The calculated thermal time constant is about ~1.2 ns for the fabricated graphene sensor, indicating that a sub-GHz operation speed is possible. The achievement will be useful for realizing ultra-fast and sensitive terahertz detectors.
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