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High hardness and low dielectric constant thin films with oriented urea oligomers by physical vapor deposition

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Abstract

Oligomers of undecylurea (OUA11) thin films with a high crystallinity, surface hardness, perpendicular orientation, and low dielectric constant were fabricated by physical vapor deposition. The thin films were composed of single OUA11, which has a relatively high molecular weight (Mw: 2500, Mn: 1200) and could be vapor-deposited without thermal decomposition. These films had a much higher crystallinity and a high surface hardness level of 9H in the pencil hardness test. The dielectric constant of the OUA11 films is estimated to be 2.1–2.3 in the frequency range of 1 Hz–0.1 MHz, which is lower than that of typical low dielectric constant (low-k) materials. These physical and electrical properties are caused by the unique structure with the molecular dipoles-oriented parallel to the electrodes on the substrate and the strong intermolecular hydrogen bonds. The unique structure could not be observed with spin-coating and is specific to the vapor-deposited films. We expect that the OUA11 films with a high hardness and a low dielectric constant can be used not only as protective coatings but also as electronic materials.

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Acknowledgements

The authors thank Unitika Ltd. for supplying OUA11 and PUA11. This work was partly supported by the MIKIYA Science and Technology Foundation and JSPS KAKENHI.

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Authors and Affiliations

  1. Department of Chemical Science and Engineering, Graduate School of Engineering, Kobe University, Rokkodai 1-1, Nada, Kobe, 657-8501, Japan

    Masahiro Morimoto, Tatsuya Fukutomi, Yasuko Koshiba & Kenji Ishida

  2. Graduate School of Science and Engineering for Research, University of Toyama, 3190 Gofuku, Toyama, 930-8555, Japan

    Masahiro Morimoto

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  1. Masahiro Morimoto
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Correspondence to Masahiro Morimoto.

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10853_2018_3000_MOESM1_ESM.tif

See supplementary materials for FT-IR RAS and transmission spectra of spin-coated OUA11 films a in the urea bond vibration region and b in the alkyl chain vibration region (TIFF 669 kb)

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Morimoto, M., Fukutomi, T., Koshiba, Y. et al. High hardness and low dielectric constant thin films with oriented urea oligomers by physical vapor deposition. J Mater Sci 54, 2483–2492 (2019). https://doi.org/10.1007/s10853-018-3000-2

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  • DOI: https://doi.org/10.1007/s10853-018-3000-2

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