Research ArticleMATERIALS SCIENCE

Ultimate suppression of thermal transport in amorphous silicon nitride by phononic nanostructure

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Science Advances  25 Sep 2020:
Vol. 6, no. 39, eabc0075
DOI: 10.1126/sciadv.abc0075
  • Fig. 1 Measured samples and patterning dimension definition.

    Scanning electron microscopy (SEM) images of amorphous Si3N4 PnCs. (A) Overall image of the sample. Al pads are deposited on the center and the edges of the suspended bridge for the thermal conductivity measurement. High-magnification SEM image of the aligned through-holes creating PnCs for pitch sizes of (B) 36 nm, (C) 100 nm, (D) 200 nm, and (E) 800 nm. The definition of pitch size P and minimum neck width n is illustrated in (E).

  • Fig. 2 Material thermal conductivity of amorphous Si3N4 PnCs.

    Material thermal conductivity of amorphous Si3N4 thin films plotted as a function of (A) the minimum neck width and (B) the surface-to-volume (S/V) ratio. Plot legends denote the pitch size of PnCs. The black dashed line in (A) represents the thermal conductivity of bare amorphous Si3N4 thin films.

  • Fig. 3 Effective thermal conductivity of amorphous Si3N4 PnCs.

    Comparison between the measured and the simulated effective thermal conductivity of amorphous Si3N4 PnCs plotted as a function of the neck width. Plot legends denote the pitch size of PnCs, where Exp. and Cal. denote Experiment and Calculation.

  • Fig. 4 Calculated thermal properties of amorphous Si3N4.

    (A) Comparison of the effective MFP of propagons and diffusons for bulk a-Si3N4 and a-Si3N4 phononic materials, taking the sample with a pitch size P of 200 nm and a hole diameter D of 175 nm as an example. (B) Comparison of thermal conductivity κ spectra for bulk a-Si3N4 and a-Si3N4 phononic materials, taking the sample with P = 200 nm and D = 175 nm as an example. (C) and (D) are the calculated thermal conductivity contribution from diffusons (κD) and propagons (κP) for all samples as a function of neck width.

  • Table 1 Lists of amorphous Si3N4 PnC structures with a thickness of 70 nm.

    Pitch (nm)PorosityDiameter (nm)Neck width
    (nm)
    360.442511
    600.303525
    600.363822
    600.393921
    1000.447030
    1000.507426
    1000.537624
    1000.598119
    2000.3913268
    2000.4714456
    2000.5415446
    2000.5816040
    2000.6917525
    4000.39262138
    4000.46285115
    4000.5731783
    8000.36506294
    8000.44557243
    8000.50594206
    16000.31935665
    16000.361013587
    16000.401063537

Supplementary Materials

  • Supplementary Materials

    Ultimate suppression of thermal transport in amorphous silicon nitride by phononic nanostructure

    Naoki Tambo, Yuxuan Liao, Chun Zhou, Elizabeth Michiko Ashley, Kouhei Takahashi, Paul F. Nealey, Yasuyuki Naito, Junichiro Shiomi

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    • Figs. S1 to S5
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