Proceedings of International Forum for Green Asia 2019
5th International Exchange and Innovation Conference on Engineering & Sciences (IEICES 2019)

GA09 / P21
Thermal Conductivity Temperature Dependence of Indium-Gallium-Zinc-Oxide Thin
Films with Three-Omega Method and Characterizing Microstructure Analysis
1

Rauf Khan1, K. Miyazaki2, R. Hattori1
Department of Applied Science for Electronics and Materials, Green Asia Program, Interdisciplinary Graduate Schoolof Engineering Sciences, Kyushu University, Japan2
Department of Mechanical and Control Engineering, Kyushu Institute of Technology, Japan
Email: rauful.karim@gmail.com

Abstract: The thermal conductivity of Indium-Gallium-Zinc-Oxide (IGZO) thin films is investigated by the differential
three-omega method at some temperatures (273K to 373K). The IGZO thin films are deposited on Al2O3 substrate by DC
magnetron sputtering at different oxygen partial pressure (PO2=0%, 10%, and 65%) and their thermal conductivities arefound to be 1.64, 1.75 and 2.58 Wm-1K-1, respectively, at room temperature. The thermal conductivities are decreasing
with increasing temperature due to the short mean free path of phonons. The mean free path is inversely proportional tothe temperature, which indicates the crystallinity inside the IGZO. We found the nanocrystalline structure with multiphaseby high resolution Transmission Electron Microscopy (HRTEM). The grain size of lattice fringes is estimated to be about
5 nm. The nano-size crystallites are oriented with the amorphous phase, but the crystalline structure is dominant.
Keywords: Three Omega (3ω) Method, Thermal Conductivity, HR-TEM, Mean-Free Path
1. INTRODUCTION
The Indium Gallium Zinc Oxide thin film transistors
have attracted numerous attention in the area of thin filmtransistor technology due to its high electron carrier
mobility, controllability with respect to electricalconductivity, low intrinsic carrier concentration andpromising optical transparency.[1] Most of the studies
have been focused on the characterizing electrical, andoptical properties of IGZO thin films but a careful studyof the thermal properties and microstructure analysis
have been lacking.[2] This study will examine thetemperaturedependency
thermalconductivity
measurement by using differential three omega (3ω)
method of IGZO thin films at high temperature to makea clear conclusion about structural analysis. We
estimated mean free path of IGZO thin films to clarify
the phonon heat conduction. TEM (TransmissionElectron Microscopy), HR-TEM (High ResolutionTransmission Electron Microscopy) and FFT (FastFourier Transmission) pattern was obtained tocharacterize microstructure analysis.
2. METHODS
Fig. 1. Plain view (a) and sectional views for a sample(b) and for a reference (c).

2.1 Thin Films Sample Preparation
IGZO thin films were deposited on 𝑎-Al2O3 substrate(Anode) having a thickness 500 nm by using DC
magnetron sputtering method. As the target, a ceramic
substance containing In, Ga, Zn (1:1:1) was used whichis cathode. The deposition conditions of DC magnetron
sputtering were as follows: the deposition power was
1000 W, the power density 1.43 W/cm2, and thedeposition pressure 0.7 Pa. The distance between thetarget and the substrate was 80 mm. The mixture of Ar
and O2 gases were used as a sputtering gas and flow rateof O2 was varied at 0%, 10%, 65%. Fig.1 shows theSchematic diagram of dimension of shadow mask,
metallic wire and IGZO thin film on 𝑎-Al2O3 substrate.

2.2. Overview of Three Omega Method3ω method employs very Cost effective and simple
thermal conductivity measurement technique. Table 1
shows the values of thermal conductivity and Fig. 1
shows the temperature dependency thermal conductivity
curve.
2.3. Overview of Focus Ion Beam (FIB) milling andTEM analysis
For TEM analysis, micro and nanoscale sample
fabrication is very important. Focus Ion beam(FIB)milling is very popular technique for nanoscale- 23 -fabrication. The FIB milling sample should be >100nm
for nanocrystal analysis. FIB milling with very low beam
current, we found surface defects top on the sample. It isvery important to do Ar milling for removing the surface
defects.

aThermal Conductivity (Wm-1K-1)

Table 1. Thermal conductivity measurement by 3ω
method and fitted value of different sample at different
temperature
SampleTemperature
ThermalConductivity(Wm-1k-1)
RT
1.69
O2 flow ratio 0%500C (323 K)
0.79
1000C (373 K)
0.71
RT
1.75
O2 flow ratio 10% 500C (323 K)
1.08
1000C (373 K)
0.7
RT
2.58
O2 flow ratio 65% 500C (323 K)
1.231000C (373 K)
1.054cOxygen Partial
Pressure = 0%
Oxygen Partial
Pressure = 10%
Oxygen Partial
Pressure = 65%

2Fig. 4. (a) shows the selective area of IGZO thin and (b)is the image of SADF (Selective area diffraction pattern)(c) High resolution transmission electron microscopy(HRTEM) image.

1

0.5
250

300

350

400

Temperature (K)Fig. 2. the temperature dependency thermal conductivityof IGZO thin film.

abconductivity of O2 flow ratio 10% IGZO thin film sample
is determined to be 1.75 Wm-1K-1 at room temperature.
Table 1 shows the thermal conductivity of different O2
flow ratio sample at different temperature. Fig.2. shows
the temperature dependency thermal conductivity. The
calculated mean free path is about 0.6 nm. Fig. 4 (b) &(c) represents the SADF pattern. From Fig. 4 (c), we haveobserved many lattice fringes which interpreted the nanocrystallinity orientation of IGZO thin film.
4. CONCLUSION
We successfully measure the thermal conductivity for the0%, 10% and 65% O2 flow ratio 500 nm IGZO thin film
at high temperature which shows the nano-crystalline
tendency. For microstructure analysis, we accomplishedthe TEM, HETEM, FFT analysis and we found the nanocrystallinity inside the amorphous IGZO. For qualitative
analysis, we fitted the value of thermal conductivity intemperature dependency thermal conductivity curve tocompare with the measurement parameter. Heat isconducted in IGZO thin film by lattice vibration. So that
we estimated the mean free path of IGZO.

bFig. 3. (a) FIB milling >100 nm thinner sample of O2
slow ratio of 10%, (b) surface defects before Ar milling

5. REFERENCES[1] K.Nomura, H. Ohta; Nature 432 (2004) 488[2] W. Lim, J. H. Jang; Appl. Phys. Lett. 93 (2008)
082102

3. RESULT & DISCUSSION
The temperature dependency thermal conductivity has
been measured at room temperature, 273 K (50 oC) and373K (100 oC) for O2 flow ratio 0%, 10% and 65%. As aresult, we measured the cross – plane thermal- 24 -