Bulk-like
Intrinsic Phonon Thermal Conductivity of
Micrometer-Thick AlN Films
Version 2 2020-06-22, 21:43
Version 1 2020-06-22, 10:14
Posted on 2020-06-22 - 21:43
Aluminum nitride (AlN) has garnered much
attention due to its intrinsically
high thermal conductivity. However, engineering thin films of AlN
with these high thermal conductivities can be challenging due to vacancies
and defects that can form during the synthesis. In this work, we report
on the cross-plane thermal conductivity of ultra-high-purity single-crystal
AlN films with different thicknesses (∼3–22 μm)
via time-domain thermoreflectance (TDTR) and steady-state thermoreflectance
(SSTR) from 80 to 500 K. At room temperature, we report a thermal
conductivity of ∼320 ± 42 W m–1 K–1, surpassing the values of prior measurements on AlN
thin films and one of the highest cross-plane thermal conductivities
of any material for films with equivalent thicknesses, surpassed only
by diamond. By conducting first-principles calculations, we show that
the thermal conductivity measurements on our thin films in the 250–500
K temperature range agree well with the predicted values for the bulk
thermal conductivity of pure single-crystal AlN. Thus, our results
demonstrate the viability of high-quality AlN films as promising candidates
for the high-thermal-conductivity layers in high-power microelectronic
devices. Our results also provide insight into the intrinsic thermal
conductivity of thin films and the nature of phonon-boundary scattering
in single-crystal epitaxially grown AlN thin films. The measured thermal
conductivities in high-quality AlN thin films are found to be constant
and similar to bulk AlN, regardless of the thermal penetration depth,
film thickness, or laser spot size, even when these characteristic
length scales are less than the mean free paths of a considerable
portion of thermal phonons. Collectively, our data suggest that the
intrinsic thermal conductivity of thin films with thicknesses less
than the thermal phonon mean free paths is the same as bulk so long
as the thermal conductivity of the film is sampled independent of
the film/substrate interface.
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Koh, Yee Rui; Cheng, Zhe; Mamun, Abdullah; Bin Hoque, Md Shafkat; Liu, Zeyu; Bai, Tingyu; et al. (2020). Bulk-like
Intrinsic Phonon Thermal Conductivity of
Micrometer-Thick AlN Films. ACS Publications. Collection. https://doi.org/10.1021/acsami.0c03978
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AUTHORS (21)
YK
Yee Rui Koh
ZC
Zhe Cheng
AM
Abdullah Mamun
MB
Md Shafkat Bin Hoque
ZL
Zeyu Liu
TB
Tingyu Bai
KH
Kamal Hussain
ML
Michael E. Liao
RL
Ruiyang Li
JG
John T. Gaskins
AG
Ashutosh Giri
JT
John Tomko
JB
Jeffrey L. Braun
MG
Mikhail Gaevski
EL
Eungkyu Lee
LY
Luke Yates
MG
Mark S. Goorsky
TL
Tengfei Luo
AK
Asif Khan
SG
Samuel Graham
KEYWORDS
500 KMicrometer-Thick AlN Films Aluminum nitrideconductivity measurementstime-domain thermoreflectancesingle-crystal AlNsingle-crystal epitaxiallyBulk-like Intrinsic Phononfilm thicknessTDTRultra-high-purity single-crystal AlN filmsfirst-principles calculationslength scalesSSTRAlN filmsbulk AlNequivalent thicknesseshigh-thermal-conductivity layerslaser spot sizepenetration depthroom temperature