Hafnium silicate glasses are high-k dielectric materials for advanced gate electronics, in particular complementary metal-oxide-semiconductor (CMOS) transistors. In this study we model HfO2-SiO2 glasses using ab-initio molecular dynamic simulations and subsequently analyze their structural, vibrational, elastic, and thermodynamic properties. As expected, we find that Si is always tetrahedrally connected to O. At low hafnia (HfO2) concentration, Hf prefers four-fold coordination, but favors higher coordination as the HfO2-content increases. The enthalpy of mixing HfO2 into SiO2 is large and indicates a low solubility of HfO2.Using linear response theory within DFPT, the phonon dispersion curves and the phonon density of states (PHDOS) are computed for the hafnium-silicate (HfSiO) models to determine their stability as well as the vibrational contribution to thermodynamic properties. Computed infrared active modes are comparable to experimental data. However, adding HfO2 to SiO2 has some intriguing effects on the vibrational properties; we observe depletion of some low-frequency vibrational modes for low HfO2-concentrations, contrary to expectations driven by the higher mass of Hf in comparison to Si. Consequently, computed heat capacities show non-linear behavior.Thus, we propose that mixing HfO2 and SiO2 can have diverse effects on the low frequency vibrational modes, which in turn can affect the thermal conductivity of such materials.

Structure and thermochemistry of Hafnium-silicate glasses

247th National Meeting (2014)

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