Materials Sciences and Applications, 2012, 3, 645-649
http://dx.doi.org/10.4236/msa.2012.39094 Published Online September 2012 (http://www.SciRP.org/journal/msa)
645
Preparation of Thin Films by a Bipolar Pulsed-DC
Magnetron Sputtering System Using Ca3Co4O9 and
CaMnO3 Targets
Weerasak Somkhunthot1, Nuwat Pimpabute1, Tosawat Seetawan2
1Program of Physics and Science Center, Faculty of Science and Technology, Loei Rajabhat University, Loei, Thailand; 2Thermoelectrics
Research Center, Faculty of Science and Technology, Sakon Nakhon Rajabhat University, Sakon Nakhon, Thailand.
Received June 7th, 2012; revised July 2nd, 2012; accepted August 5th, 2012
ABSTRACT
The thin films were deposited on the glass substrates by an asymmetric bipolar pulsed-dc magnetron sputtering system
using the Ca3Co4O9 (p-type) and CaMnO3 (n-type) targets of 60 mm diameter and 2.5 mm thickness. The targets were
prepared from powder precursors, which obtained by a solid state reaction. Optical emissions from plasmas during
sputter depositions of films were detected using a high resolution spectrometer. Thickness of thin film was estimated by
Tolansky’s Fizeau fringe method and ellipsometic measurement. Crystal structures were studied from X-ray diffraction.
The thermoelectric properties were assessed from Seebeck coefficient and electrical resistivity measurements at room
temperature. The power factors were calculated. It was found that the optical emission spectrums showed that the Ca,
Mn, Co and O atoms were sputtered from the targets onto glass substrates. As-deposited Ca-Co-O and Ca-Mn-O films
thickness values were 0.435 m and 0.449 m, respectively. The X-ray diffraction patterns clearly showed amorphous
nature of the as-deposited films. Determining thermoelectric properties of Ca-Co-O film gave Seebeck coefficient of
0.146 mV/K, electrical resistivity of 0.473 cm, and power factor of 4.531 µW/mK at room temperature. Ca-Mn-O
film baring a high resistance was not the experimental determination of thermoelectric properties.
Keywords: Thermoelectric Thin Film; Ca3Co4O9; CaMnO3; Bipolar Pulsed-DC Magnetron Sputtering System
1. Introduction
In the past, the metal coating in form of thin films to im-
prove the quality of material was done by electroplating
process which is often also called electro-deposition. The
disadvantage of electroplating was harmful to the environ-
ment. Subsequently, the vacuum depositions were devel-
oped in chemical vapor deposition (CVD) and physical va-
por deposition (PVD). CVD is a technique whereby gase-
ous reactants can be deposited onto a substrate. However,
often dangerous by-products are removed by gas flow. PVD
is a clean coating technology that involves evaporation and
deposition of a material. Material vaporizes are removed
from a source by physical processes such as evaporation
sputtering and it is transported in the form of a vapor atomic
beam through a vacuum to the substrate. Magnetron sput-
tering is one of PVD methods, which are widely used in
thin film technology. The various types of magnetron sput-
tering technique are direct current (DC), alternating current
(AC), radio frequency (RF), and pulsed-dc [1]. Pulsed-dc
magnetron sputtering is one of the latest developments of
sputtering technology for thin films deposition, which has
many advantages over others. Namely, it is versatile and
provides the ability to deposit thin films of oxide com-
pounds at high deposition rate and to eliminate arcing
problems of poisoned targets [2]. This is interested to
apply the deposition technology. It may be possible to
customize the deposition conditions so that the thin films
of highly preferred orientation can be grown.
In this work, the depositions of thin films have been car-
ried out by a bipolar pulsed-dc magnetron sputtering sys-
tem using the Ca3Co4O9 and CaMnO3 targets, which were
made from powder precursors obtained from the solid state
reaction (SSR) route. Optical emissions from plasmas dur-
ing sputter deposition of thin films were measured using
a high resolution spectrometer. Crystal structures of the as-
deposited films were studied from X-ray diffraction (XRD).
The thickness of thin films and thermoelectric properties
were investigated.
2. Experimentation
The preparation of thin films by a pulsed-dc magnetron
sputtering system is shown in Figure 1 [3]. The details of

Preparation of Thin Films by a Bipolar Pulsed-DC Magnetron Sputtering System Using Ca3Co4O9 and CaMnO3 Targets
646

on
t

off
t Time
Cathode
Anode
100 High Voltage Probe
Oscilloscope
Bipolar
Pulsed-DC
Power
Supply
+V
V
+
 

off
t
on
t
Vacuum
Chamber
Magnetron
Sputtering
Gun, Target
Argon (Ar)
Substrate
Figure 1. Experimental setup of a bipolar pulsed-dc magnetron
sputtering system.
deposition conditions, plasma and characterizations, and
thermoelectric properties measurements are given below.
2.1. Deposition Conditions
The sputtering targets were the p-Ca3Co4O9 and n-CaMnO3
pellets of 60 mm diameter, 2.5 mm thickness, 3.218 and
2.862 g/cm3 densities, respectively. The glass slide substr-
ates of 1.0 mm thick in dimension 25.0  50.0 mm2 were
used. The substrates were placed at a distance of 5.0 cm
above the targets and no additional heating was applied.
To generate the pulsed-dc plasma and initiate the thin film
deposition, the vacuum chamber was pumped down to a
base pressure of 2.00 N/m2 and flushed with high purity
argon (Ar 99.999%) gas flow rate of 15.0 ± 0.1 sccm the
total working pressures was 5.33 N/m2 for sputtering from
the Ca3Co4O9 and CaMnO3 targets. The pulse off time was
kept constant at 14 s (off and off
t). The reverse posi-
tive and cathode negative pulse widths of the power supply
were fixed at 10 s (on ) and 20 s (on
t), respectively.
These values of timings give the corresponding pulse
frequency of 17.24 kHz. The anode positive power was
set to be the same current-voltage of 20 mA and 100 V.
The cathode negative current fixed at 120 mA, the output
voltage were about 260 - 280 V with deposition time of
60 minutes. Here are the optimal conditions for the depo-
sition, which are summarized in Table 1.
t


t
2.2. Plasma and Characterizations
Optical emissions from plasma during sputter deposition
of films were observed in the wavelength range of 360 -
800 nm using a high resolution spectrometer (the getSpec-
2048 spectrometer, Sentronic GmbH) as shown in Figure
2. The spectral lines were indexed to the ASD data infor-
mation of National Institute of Standards and Technology
[4]. Crystal structures of as-deposited films were investi-
gated by X-ray diffractometer (PW3043 Philips X-ray dif-
fractometer of the Netherlands) at room temperature using
CuKα radiation,
 = 0.15406 nm. Each film was meas-
ured in the 2-theta angle range of 10˚  2θ  70˚ with scan-
ning rate of 0.02˚/s. Thin film thickness can be estimated
from the optical interference using Tolansky’s Fizeau fringe
method which is now accepted [5]. The thickness (t) of the
Table 1. Deposition conditions of thin films.
Ar Flow RateFrequency Positive Pulse Negative Pulse
 sccm kHz mA V mA  - V
Plasma
High Resolution
Spectrometer
Window
DetectorSubstrat e
Target
Vacuum Chamber
Figure 2. Observation of optical emission from plasma during
sputter deposition.
film is given by Equation (1) [6],
2
x
tx



 


 

  (1)
where x is the displacement of fringes at step, x is the
distance between consecutive fringes, and
 is the wave-
length of monochromatic light. The experimental arrange-
ment and fringe pattern is shown in Fi gure 3 . The film thic-
kness was measured by the Ellipsometer (Model L 115 S
300, Gaertner Scientific Corporation, USA) for com-
parison of the calculated values of thickness.
2.3. Thermoelectric Properties Measurements
The measurement of thermoelectric properties at room tem-
perature in air by the Keithley instruments included the
charge carrier, Seebeck coefficient, and electrical resistiv-
ity. The experimental setups can be elucidated as follows.
Firstly, the charge carrier and Seebeck coefficient were
determined by hot probe method [7,8] as shown in Fig-
ure 4. The hot and cold junctions between across two ends
of a film were connected to the digital voltmeter (Keithley
617 Programmable electrometer). The temperatures TH
and TC were sensed using the type K thermocouples, which
were connected to the digital thermometers (7563 Digital
thermometer, Yokogawa). The silicone thermal insulator
pads were placed between junctions and thermocouples.
The resistor of 10 W 5  was used to heat at hot junction
by applying currents to a resistor placed on hot side. See-
beck coefficient (S) was measured by the relation between
thermoelectric voltage (V) and temperature difference
(T). The S is defined as [8]:
V
ST

 (2)
Secondly, the electrical resistivity was measured by four-
point probe method, which can be conveniently determined
by the Van der Pauw resistivity measurement technique
[9] as shown in Figure 5. All contacts were made by silver
paste, which showed ohmic characteristics over a wide
range of currents. The current-voltage characteristics for

Preparation of Thin Films by a Bipolar Pulsed-DC Magnetron Sputtering System Using Ca3Co4O9 and CaMnO3 Targets 647
Glass Slide Substrate
x
x
Monochromatic Light
Eye Piece Fringe Pattern
Partial Reflector
Film Thickness t x
x

2
=
Sample Film
Figure 3. Experimental arrangement for Tolansky’s Fizeau
fringe method.
Film Silver Paste
Silicone Pad
Thermocouple
Wires
Glass Slide Substrate
Silver Paste
Silicone Pad
V
Digital
Thermo met ers
T
C
T
H
Figure 4. Side view (vertical cross section) of charge carrier
and Seebeck coefficient measurement.
Glass Slide Substrate
Film
a b
c d
V
A
Figure 5. Thre e-dime nsional top view of elec tric al re sistiv ity
measurement.
measurement of resistivity (  ) are measured. The  can
be estimated from [9]
ab,dc bc,adab,dc
b
c,ad
π
ln2 2
RR R
tFR






 


(3)
where t is the film thickness, Rab,dc = dc ab VI, Rbc,ad =
ad bc
VI, and F is correction function which can be
calculated from



ab,dc bc,adab,dc bc,adln2RR RRF
arccosh

exp ln22F

.
Finally, the thermoelectric efficiency can be examined
from power factor (P), which was calculated from the S
and  in Equation (4) [7,10].
3. Results and Discussion
The results and discussion of plasma, characterizations, and
thermoelectric properties are given below.
3.1. Plasma and Characterizations
The cathode voltage waveforms, photographs of stable
glow discharges, and optical emission spectrums of the bi-
polar pulsed-dc magnetron argon discharge during the sput-
tering of the Ca3Co4O9 and CaMnO3 targets are shown in
Figure 6. These results indicated the good pulsed-dc plas-
ma characteristics. The spectral lines were indexed to the
ASD data information of NIST [4]. It was found that the
emission lines of Ar (422.57, 656.34, 696.66, 706.83,
738.55, 750.50, 751.57, 763.63, 772.51, 794.94 and 797.25
nm), Ca (370.26, 393.36 and 396.85 nm), Co (361.46 and
399.43 nm), and Mn (361.06 and 403.11 nm) were promi-
nent features. The emission line of O (777.41 nm) was de-
tected, but it is not intense due to the strong line of this
species is not in measured range. The optical emission
spectrums showed that Ca, Co, Mn, and O atoms were
sputtered from the targets. Hence, it can be expected that
400 500 600700 800
(b) CaMnO3
Ar: 696.66 nm
Mn: 403.11 nm
O: 777.41 nm
Ar: 794.94, 797.25 nm
Ar: 772.51 nm
Ar I: 763.63 nm
Ar: 750.50, 751.57 nm
Ar: 738.55 nm
Ar: 706.83 nm
Ar: 656.34 nm
Ar: 422.57 nm
Ca: 393.36, 396.85 nm
Ca: 370.26 nm
Mn:361.06 nm
Optical Emission Intensity
Wavelength (nm)
20 mA, +100±5 V
120 mA, 275±5 V
Waveform
Photograph
400 500 600700 800
(a) Ca3Co4O9
Ar: 696.53 nm
Co: 399.43 nm
O: 777.41 nm
Ar: 794.94, 797.25 nm
Ar: 772.51 nmAr I: 763.63 nm
Ar: 750.50, 751.57 nm
Ar: 738.55 nm
Ar: 706.83 nm
Ar: 656.41 nm
Ar: 422.57 nm
Ca: 393.36, 396.85 nm
Ca: 370.26 nm
Co: 361.46 nm
Optical Emission Intensity
Wavelength (nm)
Waveform
20 mA, +100±5 V
120 mA, 265±5 V
Photograph
Figure 6. Waveforms, photographs, and spectral lines dur-
ing the sputtering of (a) Ca3Co4O9 and (b) CaMnO4.

Preparation of Thin Films by a Bipolar Pulsed-DC Magnetron Sputtering System Using Ca3Co4O9 and CaMnO3 Targets
648
the deposited films will contain these atomic species.
From this point onward, the deposited films will be re-
ferred to as Ca-Co-O and Ca-Mn-O containing. The
as-deposited films of 1.60  1.60 cm2 and XRD patterns
are shown in Figure 7. From this figure clearly indicated
amorphous nature of the as-deposited films. This was
expected since the substrates were not heated during the
deposition process. Therefore, the kinetic energy of
atomic species at the substrate surface was not enough to
promote the growth of a crystal. Each film thickness was
initially estimated using optical interference method (yel-
low sodium light,
 = 589.3 nm) and was obtained from
ellipsometic measurement (red laser light,
 = 632.8 nm).
The results are given in Table 2. The results of meas-
urement gave the thickness of 435.31 nm and 449.35 nm
for as-deposited Ca-Co-O and Ca-Mn-O films, respec-
tively.
3.2. Thermoelectric Properties
The results of investigations on thermoelectric properties
of Ca-Co-O and Ca-Mn-O films such as the types of charge
carrier, Seebeck coefficient, electrical resistivity, and power
factor are presented and discussed.
Firstly, the types of charge carriers were determined by
hot probe method (see Figure 4). The result of measure-
ment on Ca-Co-O film, the cold junction showed higher
voltage than the hot junction, indicating that the holes con-
duction dominated transport property (p-type). The meas-
urement results of relation between Seebeck emf (V) and
temperature difference (T) are shown in Figure 8. Ca-
Co-O film indicated linear dependence between V and
10 20 30 40 50 60 70
Intensity (counts)
2 (degree)
(a) As-deposted Ca-Co-O Film
(a) As-deposted Ca-Mn-O Film
(b) As-deposited Ca-Mn-O Film
(a) As-deposited Ca-Co-O Film
(b)As-deposited Ca-Mn-O Film
(a)As-deposited Ca-Co-O Film
Figure 7. As-deposited Ca-Co-O and Ca-Mn-O films of 1.60 
1.60 cm2 and XRD patterns.
Table 2. Thickness of the as-deposited Ca-Co-O and Ca- M n- O
films.
Samples Calculation
(nm)
Measurement
(nm)
Refractive
Index
Ca3Co4O9
CaMnO3
~441.98
~452.50
435.31  3.37
449.35  1.27
2.22  0.01
2.06  0.01
024681012 14 16 18 20
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
(b) Ca-Mn-O Film: S = 0
(a) Ca-Co-O Film: S = 146.35 9.69 V/K


Seebeck emf (mV)
Temperature Difference (K)
Figure 8. Seebeck emf of thin films as a function of tempera-
ture difference (a) Ca-C o-O film and (b) C a-Mn-O film.
T, the S of 146.35 V/K is obtained. Ca-Mn-O film bar-
ing a high resistance was not the experimental determi-
nation of charge carrier and Seebeck coefficient.
Secondly, the current-voltage characteristics were ob-
tained by the Van der Pauw four-probe measurement (see
Figure 5). The experimental result of Ca-Co-O film is
shown in Figure 9. The plot exhibited good ohmic I-V
characteristics. The  value obtained from this I-V plot, it
is 0.473 cm. For the experimental measurement of Ca-
Mn-O film could not be determined.
Finally, the power factor was calculated from S and 
in Equation: 2 PS

. The result of Ca-Co-O film gave
value of 4.53 µW/mK.
4. Conclusion
The preparation of Ca-Co-O and Ca-Mn-O thin films
using a bipolar pulsed-dc magnetron sputtering system
were successfully deposited on glass substrates from the
Ca3Co4O9 and CaMnO3 targets, respectively. The XRD
patterns clearly indicated amorphous nature of the as-depo-
sited films. Determining thermoelectric properties of Ca-
Co-O film showed the low Seebeck coefficient and high
electrical resistivity, which leaded to a low power factor.
Ca-Mn-O film baring a high resistance was not an experi-
ment. The post deposition annealing and doped metals have
been expected candidates for good thermoelectric prop-
erties. This will be further investigated.
5. Acknowledgements
This work was financially supported by the Research and
Development Institute, Loei Rajabhat University (LRU).
The Thermoelectric Research Center (TRC) and Sakon
Nakhon Rajabhat University (SNRU) are acknowledged
for the preparation of sputtering targets. Asst. Prof. Dr.
Thanusit Burinprakhon, the Physics Department, Faculty of

Preparation of Thin Films by a Bipolar Pulsed-DC Magnetron Sputtering System Using Ca3Co4O9 and CaMnO3 Targets
649
-0.3-0.2-0.10.0 0.1 0.2 0.3
-0.8
-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
0.8


Rab,cd = 2.187 0.021 k
V
dc (V)
Iab (mA)
(a)
-0.3-0.2-0.10.0 0.1 0.2 0.3
-0.8
-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
0.8


Rbc,ad = 1.983 0.007 k
V
bc (V)
Iad (mA)
(b)
(a) (b)
-0.3-0.2-0.10.0 0.1 0.2 0.3
-0.8
-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
0.8


Rcd,ab = 2.472 0.009 k
V
ab (V)
Idc (mA)
(c)
-0.3-0.2-0.10.00.1 0.2 0.3
-0.8
-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
0.8


Rad,bc = 3.037 0.146 k
V
ad (V)
Ibc (mA)
(d)
(c) (d)
Figure 9. Plot of the current-voltage characteristics for the electrical resistivity measurement of Ca-Co-O film (a) Iab-Vdc; (b)
Iad-Vbc; (c) Idc-Vab and (d) Ibc-Vad.
[4] J. Curry, “NIST Atomic Spectra Database,” 2012.
http://www.nist.gov/pml/data/asd.cfm
Science, Khon Kaen University (KKU) is gratefully ac-
knowledged for kind help with preparation of thin films by
an asymmetric bipolar pulsed-dc magnetron sputtering sys-
tem and thermoelectric characterizations.
[5] S. Tolansky, “An Introduction to Interferometry,” Kong-
mans, Green & Co. Ltd., London, 1955.
[6] K. Jayachandran, “Electrical, Optical and Structural Studies
in Bismuth, Antimony, Bismuth Oxide and Antimony
Oxide Thin Films,” Ph.D. Thesis, Mahatma Gandhi Uni-
versity, Kerala, 1997.
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