Tokyo Institute of Technology
Kamiya-Katase Group

  • Hosono
    Gr.
  • Japanese

Research topics

Novel functional materials and devices in uncultivated fields and ideas

Amorphous Oxide Semiconductor (AOS)
IGZO  In 2004 and before, it had been believed “good semiconductor” can be realized only in crystalline materials such as Si, GaN, and ZnO. Notwithstanding that, we demonstrated the high-performance thin-film-transistor (TFT) can be realized by amorphous oxide semiconductor “IGZO”, In-Ga-Zn-O. Although “IGZO” has an amorphous structure, transparent flexible high-performance TFT can be produced. Our IGZO TFT is already in mass production in iPad, Surface Pro4, and 77-inch OLED TVs. In addition, we recently succeeded to demonstrate room-temperature fabrication of inorganic light-emitting semiconductor films, which will be used for optical devices and displays, replacing OLED in the future.
[Ref.] K. Nomura et al., Nature (2004), Science (2003).

 

Transparent conductor using covalent bonds
IGZO  Germanium oxide (GeOx) is known as a good electrical insulator with a wide bandgap over 6 eV. We demonstrated to convert SrGeO3 to a good transparent conductor. Quantum calculation explains its electronic structure and why it reduce sthe bandgap down to 2.7 eV by employing the cubic SrGeO3 structure. Like this, we are making continuous challenges to create new functional materials based on our original material design concept.
[Ref.] H. Mizoguchi et al., Nature Commun. (2011).

 

Ultrawide gap amorphous oxide semiconductor
IGZO  As explained above, it had been believed the AOS does not have good electronic properties, but we then overturned this misunderstanding by IGZO TFTs. Next our target is ultrawide gap AOSs, which has been believed not to been realized until now. We recently realized GaOx AOS with a large bandgap of 4.12 eV by controlling the defects and understanding the doping mechanism in AOSs.
[Ref.] J. Kim et al., NPG Asia Mater. (2017).

 

Energy harvesting materials using ambient “small heat“
IGZO  Although we don’t recognize, we have unlimited energy of “small heat” in our life, but we cannot use them for electronic devices at present. If we realize new energy harvesting materials and devices converting the “small heat” to useful electricity, so called IoT, inter-networking society to connect everything, will be realized as the communication devices will operate only by the ubiquitous energy without battery. In order to realize such high-efficiency and power-saving devices, we have been challenging to create high-performance thermoelectric material by the thin-film-growth technique and proposed new ideas and mechanism for the enhancement of energy conversion efficiency. [Ref.] C. Yamamoto et al., Adv. Funct. Mater. (2020).Titech News, T. Katase et al., Advanced Science (2021).Titech News, M. Kimura et al., Nano Letters (2021).Titech News, X. He et al., Advanced Science (2021).Titech News

 

断熱と放熱を自発的に制御する熱制御材料
IGZO  日本における一次供給エネルギーのうち約1/3は電力や動力などに利用されていますが、残りの約2/3は廃熱として環境中に排出されています。このため、廃熱エネルギーの削減と有効利用は、深刻化するエネルギー問題を解決する重要な課題です。物質内を流れる熱量は、物質の両端に発生する温度勾配と熱伝導率(熱の流れやすさ)に比例します。そのため、熱伝導率が低い材料は熱を流さない断熱材に、また、熱伝導率の高い材料は熱を流す放熱材として用いられています。一方、そのように一定の熱伝導率を持つのではなく、一つの材料で熱伝導率を変化させられれば、流れる熱量を制御することができ、断熱・放熱の切り替えといった、今までにない高度な熱制御を実現できる可能性があります。例えば、低温から高温にかけて熱伝導率が急激に増加する材料があれば、低温側では断熱し、高温側では逆に放熱する機能を持たせることができますが、これまで熱伝導率が大きく変化する材料の例は極めて少なく、熱伝導制御材料の開発は難易度の高い課題とされてきました。このような背景のもと、当研究室では、結晶構造の次元性が温度変化によって可逆的に変化し、低温で断熱して高温で放熱する熱伝導制御材料を開発しました。今後、全く新しい材料設計により、さらに熱伝導率を大きく制御できる材料を開発し、温度管理が重要な自動車の触媒やバッテリ等に応用すれば、デバイスの温度が自発的に調整され、効率のよい熱利用が期待できます。
[関連論文] Y. Nishimura et al., Adv. Electron. Mater. (2022).プレスリリース

 

Development of new functional materials & devices by nanoscale-controlled thin-film growth and high electric-field approach
IGZO IGZO    Unique properties, can not be observed in bulk, appear by preparing the artificial hetero-structure or by controlling the carrier densities and electric potential in materials using external electric field. We aim to develop new functional thin-films and opto-electronic/electro-magnetic devices using nanoscale-controlled thin-film growth and high electric-field approach. For example, we succeeded to realize Josephson junction and superconducting quantum interference devices of iron pnictide superconductors by forming the artificial grain boundary junctions in thin films. We also proposed a solid phase epitaxy method to regularly align different cations in thin film material and realized the single crystalline film of ferromagnetic oxide semiconductor, leading to the all oxide ferromagnetic junction devices.
[Ref.] T. Katase et al., Nature Commun. (2011)., PNAS (2014)., Adv. Electron. Mater. (2015, 2015, 2016)., Sci. Rep. (2016)., Science Adv. (2021).Titech News , X. He et al., ACS Appl. Mater. Interfaces (2022).

 

Computer-assisted materials science & materials design

IGZO  We use first-principles calculations, molecular dynamics simulations, device simulations, etc for designing our new materials and also for revealing the underlying mechanism of their functions. It is usually difficult to find new materials, but we challenge to develop novel functional materials by understanding “why the material show good properties”, predicting “how we can improve the material properties”, and confirming the idea experimentally. One of our approaches is shown in the electron density map of 12CaO・7Al2O3 (C12A7) with 0.4nm-size cage. Usually, electrons in the conventional semiconductor conduct through the positions of atoms, but for C12A7, the electrons pass through the cages, which can be visualized by the quantum calculation. By collaboration of experiment and theory, we always try to understand the underlying mechanisms and to find a way to develop novel functional materials.