T H Heat flow across a SiO2 layer EXAS TEC Motivation Si|SiO2 interfaces are ubiquitous in Si technology. How does heat generated by a CPU in Si interact with this layer? Our study: ‘first-principles’ theory Existing theoretical studies: all are empirical [1-5] Experiment: focus on the ‘interface boundary resistance’ [8-10] Interface vibrational modes ΔT 1 ΔT 2 𝑇0 𝑇ℎ𝑓 𝑇0 = background T 𝑇ℎ𝑓= heat front T as it reaches the interface ΔT 1 = ‘low-T’ window ΔT 2 = ‘high-T’ window Result: monitoring heat flow Theory Electronic structure: SIESTA[7] valence regions: DFT (LDA) core regions: ab-initio pseudopotentials Nuclei classical Host material H-saturated Si nanowire in a large 1D- periodic box (strictly microcanonical) Non-equilibrium MD: ‘supercell preparation’ technique [6] NO thermostat or thermalization runs excellent T control t=0: distribution of normal vibrational modes with random phases averaging: 20-30 microstates Physics Department T EXAS TEC H U N I V E R S I T Y Christopher M. Stanley and Stefan K. Estreicher Heat flow across a SiO2 layer Result: oxide layer is a barrier to heat flow With an oxide: considerably more time needed to equilibrate With oxide: time constant increases by factors of 2.4 (low-T window) to 2.3 (high-T window) Difference between the T windows: due to difference in thermal conductivity of nanowire at different temperatures With Oxide Without Oxide Oxide construction: a-SiO2 layer Simulate experimental approach repeat steps 1-3 remove self-interstitial when needed coordinates relaxed by CG one O2 molecule added at a time Construction Summary Typical initial position O2 final structure: Si230O54H56 Set up a T gradient at t=0 A slice of the nanowire is heated above background temperature (T0) at t=0 MD run: the heat initially flows only to the right Temperature gradients are chosen based on frequency range of oxide-related vibrational modes [1] B. Deng et al., J. App. Phys. 115, 084910 (2014). [2] S.S .Mahajan et al., Therm. Thermomech. Phenom. Ele. Sys. 1055 (2008) [3] E. Lampin et al., Appl. Phys. Lett. 100, 131906 (2012) [4] J Chen et al. J. App. Phys. 112, 064319 (2012) [5] S. Munetoh et al., Comput. Mater. Sci. 39, 334 (2007) [6] T.M. Gibbons et al., J. App. Phys. 118, 085103 (2015) [7] J.M. Soler, et al., J. Phys. Cond. Matt. 14, 11 (2002) [8] D.H. Hurley et al. J. App. Phys. 109,083504 (2011) [9] R Kato et al. Int J Thermophys. 29, p2062-2071 (2008) [10] S.M. Lee. J. App. Phys. 81, p2590-2595 (1997) References Oxides:barriers to heat flow The heat generated in the Si (e.g. by a CPU) finds it harder to escape The results point towards the possibility of non-propagating vibrational modes, which cannot be explained by conventional models of heat flow. Conclusions