One quasi-direct gap phase (Amm2) and three indirect gap phases (C2/m-16, C2/m-20, and I-4) of silicon allotropes are proposed. The detailed theoretical study on the structure, density of states, elastic properties, sound velocities, and Debye temperature of these four phases is carried out by using first principles calculations. The elastic constants of these four phases are calculated by strain-stress method. The elastic constants and the phonon calculations manifest all novel silicon allotropes in this paper are mechanically and dynamically stable at ambient condition. The B/G values indicate that these four phases of silicon are brittle materials at ambient pressure. The anisotropy properties show that C2/m-20 phase exhibits a larger anisotropy in its elastic modulus, shear elastic anisotropic factors, and several anisotropic indices than others. We have found that the Debye temperature of the four novel silicon allotropes gradually reduces in the order of C2/m-20 > Amm2 > C2/m-16 > I-4 at ambient pressure. V

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Coaxial through silicon via (TSV) is a promising technology in three dimensional integrated circuits (3D ICs). Conventional coaxial TSV offers shield around part of the TSV in silicon substrate leave the two ends of TSV and the whole pad without any shield. This paper reports a new coaxial TSV, which offers more shields around TSV and pad with gaps for interconnection. Furthermore, the new structure is more feasible by using double dielectrics with considering deformation and process error. The full-wave extraction simulation result shows that the new structure offers less coupling with adjacent TSVs than conventional coaxial TSV structure does. The losses of new structure is lager but can be reduced by increasing the thickness of gap.

Two new Group IV element allotropes Si3 and Ge3 in P6222 phase are predicted in this work and their physical properties are investigated using the density functional theory. Each of the newly predicted allotropes has a superdense structure, which is mechanically, dynamically, and thermodynamically stable, as verified by elastic constants, phonon dispersion spectra and relative enthalpies, respectively. The mechanical anisotropy properties are studied in detail by illustrating the directional dependence of Young’s modulus, discussing the universal anisotropic index, and calculating shear anisotropy factors together with bulk moduli. It shows that P6222–Si3 exhibits the greater anisotropy than P6222–Ge3, and interestingly both of the newly predicted crystals appear to be isotropic in the (001) plane. Additionally, the Debye temperature, sound velocities, and the minimum thermal conductivity are examined to evaluate the thermodynamic properties of C3, Si3, and Ge3 in P6222 phase, and the electronic band structures are achieved by HSE06 hybrid functional, which indicate that P6222–C3 and –Si3 are indirect band gap semiconductors and P6222–Ge3 exhibits the metallic feature.