Thermal phonon spectroscopy of phononic crystals by using a MEMS thermometer

2018 Fiscal Year Final Research Report

• Project/Area Number: 17K14654
• Research Category: Grant-in-Aid for Young Scientists (B)
• Allocation Type: Multi-year Fund
• Research Field: Electronic materials/Electric materials
• Research Institution: Tokyo University of Agriculture and Technology (2018); The University of Tokyo (2017)
• Principal Investigator: Zhang Ya 東京農工大学, 工学(系)研究科(研究院), 准教授 (80779637)
• Research Collaborator: Hirakawa Kazuhiko ; Nomura Masahiro
• Project Period (FY): 2017-04-01 – 2019-03-31
• Keywords: フォノン分光法 / フォノニック結晶 / 熱輸送 / MEMS / 半導体 / マイクロ/ナノ構造

Outline of Final Research Achievements

We have utilized a novel MEMS thermometer as a powerful tool for studying the thermal transport in phononic crystals(PnC). We fabricated two-dimensional PnCs on GaAs MEMS beam. By measuring the thermal decay time of the beams with and without PnCs, we obtained the change in thermal conductance of MEMS beams by PnCs. When the hole diameters in PnCs were decreased to ~300 nm, the PnCs gave notably larger drops in thermal conductance than the theoretical expection, suggesting that the phononic effect changed the thermal conductivity of the GaAs material.
Furthermore, we sent two light pulses from a femtosecond laser with a modulated time delay to heat up the MEMS beam, and we measured its temperature rise as a function of the time delay between two pulses, which gives a phonon interference pattern owing to the coherent phonon transport in the GaAs beam. By performing Fourier transform, we determined the phonon spectrum through the GaAs beam.

Free Research Field

半導体マイクロ・ナノ構造

Academic Significance and Societal Importance of the Research Achievements

本研究は、超高速フォノン分光法を実施するための強力な方法を提供し、半導体マイクロ/ナノ構造における熱輸送プロセスに対する理解を大きく深化させるものである。さらに、その知見が、マイクロ/ナノ材料の熱特性における多くの研究に広く応用できるため、基礎研究と社会の両方に大きなインパクトを与える。従って、本研究に基づき、更なる研究の開拓が期待できる。将来的には、フォノンの波動性による熱輸送の制御を可能にし、半導体デバイスに対する理想的な熱制御につながり、エネルギー効率の高い社会の構築にも役立つと期待できる。