am6b15014_si_001.pdf (1.64 MB)
Control of Nanoplane Orientation in voBN for High Thermal Anisotropy in a Dielectric Thin Film: A New Solution for Thermal Hotspot Mitigation in Electronics
journal contribution
posted on 2017-02-10, 00:00 authored by Olivier Cometto, Majid K. Samani, Bo Liu, Shuangxi Sun, Siu Hon Tsang, Johan Liu, Kun Zhou, Edwin H. T. TeoHigh anisotropic thermal materials,
which allow heat to dissipate in a preferential direction, are of
interest as a prospective material for electronics as an effective
thermal management solution for hot spots. However, due to their preferential
heat propagation in the in-plane direction, the heat spreads laterally
instead of vertically. This limitation makes these materials ineffective
as the density of hot spots increases. Here, we produce a new dielectric
thin film material at room temperature, named vertically ordered nanocrystalline
h-BN (voBN). It is produced such that its preferential thermally conductive
direction is aligned in the vertical axis, which facilitates direct
thermal extraction, thereby addressing the increasing challenge of
thermal crosstalk. The uniqueness of voBN comes from its h-BN nanocrystals
where all their basal planes are aligned in the direction normal to
the substrate plane. Using the 3ω method, we show that voBN
exhibits high anisotropic thermal conductivity (TC) with a 16-fold
difference between through-film TC and in-plane TC (respectively 4.26
and 0.26 W·m–1·K–1).
Molecular dynamics simulations also concurred with the experimental
data, showing that the origin of this anisotropic behavior is due
to the nature of voBN’s plane ordering. While the consistent
vertical ordering provides an uninterrupted and preferred propagation
path for phonons in the through-film direction, discontinuity in the
lateral direction leads to a reduced in-plane TC. In addition, we
also use COMSOL to simulate how the dielectric and thermal properties
of voBN enable an increase in hot spot density up to 295% compared
with SiO2, without any temperature increase.