LiNbO3 thin films were deposited on Al2O3 substrates by RF-magnetron sputtering with in-situ electric
field to study the self-polarization effect. The films have been characterized crystallographically by x-ray
diffraction, and morphologically by atomic force microscopy. The films contain crystallites of LiNbO3 with
preferable orientation [012] along the normal to the Al2O3 substrate surface (012). Piezoresponse force
microscopy was used to study vertical and lateral polarization direction in LiNbO3 thin films. The analysis
of the histograms of vertical piezoresponse images allowed to reveal self-polarization effect in films. The
local piezoelectric hysteresis performed on the nanometer scale indicates switching behavior of polarization
for LiNbO3 thin film

Bykov, A.S.

Chichkov, M.V.

Kiselev, D.A.

Ksenich, S.V.

Kubasov, I.V

Malinkovich, M.D.

Parkhomenko, Yu.N.

Shcherbachev, K.D.

Temirov, A.A.

Timushkin, N.G.

Voronova, M.I.

Zhukov, R.N.

SocioEconomic Challenges Journal (Sumy State University)

JOURNAL OF NANO- AND ELECTRONIC PHYSICS ЖУРНАЛ НАНО- ТА ЕЛЕКТРОННОЇ ФІЗИКИ 
Vol. 8 No 4(1), 04025(4pp) (2016) Том 8 № 4(1), 04025(4cc) (2016) 
 
 
2077-6772/2016/8(4(1))04025(4) 04025-1  2016 Sumy State University 
Synthesis and Nanoscale Characterization of LiNbO3 Thin Films Deposited on Al2O3 
Substrate by RF Magnetron Sputtering under Electric Field 
 
R.N. Zhukov*, D.A. Kiselev, K.D. Shcherbachev, M.I. Voronova, S.V. Ksenich, I.V. Kubasov,  
A.A. Temirov, N.G. Timushkin, M.V. Chichkov, A.S. Bykov, M.D. Malinkovich, Yu.N. Parkhomenko 
 
National University of Science and Technology "MISiS", 4, Leninskiy pr., 119049 Moscow, Russian Federation 
 
(Received 18 October 2016; published online 29 November 2016) 
 
LiNbO3 thin films were deposited on Al2O3 substrates by RF-magnetron sputtering with in-situ electric 
field to study the self-polarization effect. The films have been characterized crystallographically by x-ray 
diffraction, and morphologically by atomic force microscopy. The films contain crystallites of LiNbO3 with 
preferable orientation [012] along the normal to the Al2O3 substrate surface (012). Piezoresponse force 
microscopy was used to study vertical and lateral polarization direction in LiNbO3 thin films. The analysis 
of the histograms of vertical piezoresponse images allowed to reveal self-polarization effect in films. The 
local piezoelectric hysteresis performed on the nanometer scale indicates switching behavior of polarization 
for LiNbO3 thin film. 
 
Keywords: Lithium niobate, Rf-magnetron sputtering, Self-polarization, Piezoresponse force microscopy. 
 
DOI: 10.21272/jnep.8(4(1)).04025 PACS numbers: 77.80.Dj, 68.55. – a, 77.55.H – 
 
 
                                                        
* rom_zhuk@mail.ru 
1. INTRODUCTION 
 
Ferroelectric thin film integration with Si and other 
integrated device substrates has the potential to enable 
new modes of photonics integration as well as a new 
class of high work/volume piezoelectric devices for 
MEMS integration. Thin films of Lithium Niobate 
(LiNbO3) posses a number of advantages over bulk 
material including the possibilities of producing step 
index profiles, selectively introducing dopants, and the 
fabrication of multilayer structures. 
Less daunting is the development of a hybrid device 
in which the infrared source and frequency doubling 
waveguide are formed on different substrates, 
precluding the need for a cladding layer and allowing 
the use of a more compatible substrate for the growth of 
the ferroelectric thin film. 
The ferroelectric thin films are intensively 
investigated because of their useful ferroelectric, 
piezoelectric, pyroelectric, and electrooptic properties 
and nonvolatile ferroelectric memories [1]. It is often 
observed that films prepared by different deposition 
techniques on different substrates possess a significant 
polarization (self-polarization) that may be almost as 
high as that produced by the subsequent poling [2 and 
references therein]. The observation of a self-
polarization state in different systems is frequently 
associated with various factors such as thickness, 
texture, different substrates/electrodes and the 
formation temperature of the ferroelectric phase. 
The self-polarization effect has been explained in 
terms of a space charge associated with the Schottky 
barriers located at the bottom film-electrode interface 
[2] or by a mechanical coupling between the 
ferroelectric film and the rigid substrate [3]. 
Piezoresponse force microscopy (PFM) is one of the 
most powerful techniques used for imaging and 
identifying domains in a ferroelectric and piezoelectric 
materials at nanoscale [4]. Recently, PFM method has 
be used to probe the self-polarization effect at the 
nanoscale level in ferroelectric materials as 
Pb(ZrxTi1 − x)O3 [5-7], Pb1 – xLax(Zr1 – yTiy)1 – x/4O3 [8] and 
Hf0.5Zr0.5O2 [9] thin films. In addition, it was reported 
that PZT and PLZT thin films with different thickness 
had influence on the self-polarization effect. 
Only very recently Kiselev et. al. showed that the 
RF magnetron sputtering of a target allows the 
synthesis of thin (~ 100 nm) lithium-niobate films on 
single-crystal silicon substrates with a high (up to 
65 %) degree of orientation of grains in which the 
polarization vector is perpendicular to the substrate 
plane and piezoelectric characteristics of the films 
greatly depend on the crystallographic orientation of 
the silicon substrates [10].  
In this paper, we continued to study influence of the 
type and crystallographic orientation of the substrate 
on the domain structure, self-polarization effect and 
piezoelectric properties of the films of lithium niobate. 
Al2O3 plate was used as substrate whose orientation is 
different from the c-direction; film deposition was 
carried out by RF-magnetron sputtering target under 
the simultaneous action of electric field directed toward 
or away from the substrate. 
 
2. EXPERIMENTAL DETAILS 
 
The LiNbO3 films 100 nm thick were deposited on 
Al2O3 (012) substrate by RF magnetron sputtering of 
the single-crystalline target in Ar/O  1 atmosphere. 
The magnetron power was 150 W. To investigate 
influence polarity of the electric field on self-
polarization, we performed the following procedure the 
synthesis LiNbO3 films in in-situ electric filed (Fig. 1). 
The top side of Al2O3 substrate was coated Ta (electrode 
#1), second electrode (electrode #2) placed at a distance 
of about 15 cm from its bottom substrate. During the 
process of deposition between Electrode №1 and 
Electrode №2 was applied DC voltage: i) + 500 V and 
 R.N. ZHUKOV, D.A. KISELEV, ET AL. J. NANO- ELECTRON. PHYS. 8, 04025 (2016) 
 
 
04025-2 
ii) – 500 V, thus the electric field intensity was about 
33-35 V/cm. 
In next we called a samples synthesized in positive 
electric field as “LiNbO3/Al2O3-@plus” (positive potential 
on electrode #1), in negative field “LiNbO3/Al2O3-
@minus”.  
 
 
 
Fig. 1 – Schematic representation deposition of lithium 
niobate thin film on Al2O3 substrate under in-situ electric 
field 
 
The phase composition of the films was determined 
by X-ray diffraction on diffractometer D8 Discover 
(Bruker-AXS, Germany). The X-ray source used was a 
copper anode X-ray tube. To increase the intensity of 
monochromatization and collimation in the diffraction 
plane, we used a Göbel mirror. The width of the x-ray 
beam irradiated the samples was of 0.2 mm. Angular 
distribution of the diffracted beam was measured using 
Bruker LynxEye 1D detector. The measurements were 
performed in 2- geometry. Experimental data were 
analyzed using the EVA program (incorporated into the 
D8 Discover diffractometer software package) and ICDD 
PDF-2 database.  
The surface morphology, and piezoelectric properties 
of the LiNbO3 thin films were characterized by the 
piezoresponse force microscopy using commercial 
scanning probe microscopes MFP-3D (Asylum Research) 
with Asyelec Ti/Ir coated conductive probes (Asyelec-01, 
Asylum Research, USA). Vertical or out-of-plane PFM 
(OOP-PFM) and lateral/in-plane PFM (IP-PFM) images 
of the samples were obtained by applying AC voltage 
(3V peak-to-peak) with the frequency around 300 kHz. 
 
3. RESULTS 
 
XRD diffraction pattern are shown in Fig. 2. To 
avoid a strong reflection (012) type from the substrate, 
the  start position were shifted for 2 from 2/2 value.  
It was found out that the both films contain 
crystallines of LiNbO3 with preferable orientation [012] 
along the normal to the Al2O3 substrate surface (012). 
However, in a case of @plus sample, the crystallines 
with planes of (110) type, which are parallel to the 
sample surface, are also revealed. 
The surface morphology of the LiNbO3 films 
synthesized on Al2O3 substrate with external electric 
field shown in Fig. 3 (a, b). On the topographic images a 
well visualized two types grains: i) “big” grains with the 
lateral grain size of which ranged from 300 to 600 nm 
and 40-80 nm in height and ii) “small” grain with 5 nm 
high and 50 nm in diameter.  
 
20 40 60 80
0
1000
2000
3000
*
*
*
(1
1
0
)
(0
2
4
)  
 
 
2, Dergee
 @minus
 @plus
(0
1
2
)
In
te
n
si
ty
, 
a
rb
. 
u
n
it
s * LiNbO
3
*
 
 
Fig. 2 –  X-ray diffraction patterns of an as-grown LiNbO3 on 
Al2O3 substrate 
 
From the statistical analysis of the topography the 
lithium niobate thin films found that its roughness 
(Rms) ~23 nm for sample LiNbO3/Al2O3 - @plus and 8 
nm for LiNbO3/Al2O3 – @minus.  
OOP-PFM and IP-PFM images obtained 
simultaneously with the topography image are shown in 
Fig. 3 (c-f) for both samples. As known, PFM can to use 
to characterize the polarization states in the 
ferroelectric materials.  
 
LiNbO3/Al2O3 – @plus LiNbO3/Al2O3 – @minus 
  
  
  
 
Fig. 3 – Topography (a, b), OOP-PFM (c, d) and IP-PFM (e, f) 
images of LiNbO3/Al2O3 heterostructures 
 
In addition, the “bright” and “dark” contrasts of 
grains on the OOP piezoresponse signal (Fig. 3 c, d), 
corresponding to a particular direction of the 
polarization vector, there is “zero” contrast, which 
corresponds to the presence of the non-ferroelectric 
(b) 
(c) (d) 
(а) 
(e) (f) 
 SYNTHESIS AND NANOSCALE CHARACTERIZATION … J. NANO- ELECTRON. PHYS. 8, 04025 (2016) 
 
 
04025-3 
particle, for example the secondary phase LiNb3O8, 
observed previously in sol-gel derived LiNbO3 films [11] 
In our case, the maximum piezoelectric response 
(positive value a signal or “bright” contrast) observed in 
the film, which implies that the polarization vector in 
this area is directed toward the lower interface. In IP-
PFM images (Fig. 3 e, f), we visualize the piezoresponse 
corresponding to the polarization direction in the plane 
of the film, which corresponds to the piezoelectric 
modulus d15. The good lateral piezoresponse signal was 
observed in sample LiNbO3/Al2O3-@plus, and these 
results correlate well with XRD data. Again, as an on 
OOP-PFM image in IP-PFM signal we not have contrast 
from “big” grain, that confirms non-ferroelectric nature 
this particles. 
Fig. 4 shows the OOP-PFM histograms of LiNbO3 
films acquired from piezoelectric out-of-plane images in 
Fig. 3 (c, d) for two samples. As known, the 
piezohistograms are statistical distributions of the 
piezoelectric signal related to the domain configuration 
in a ferroelectric such as for out-of-plane polarization 
the vertical tip displacement is due to the effective d33 
piezoelectric coefficient. Thus, the observed peaks in 
these distribution curves are associated with the most 
probable domain configuration while the peak width is a 
measure of a number of domain states [8]. 
 
-100 -50 0 50 100 150
0.0
0.2
0.4
0.6
0.8
1.0
 
 
N
o
rm
a
li
ze
d
 i
n
te
n
si
ty
, 
a
rb
. 
u
n
it
s
Piezoresponse, arb.units
1
2
 
 
Fig. 4 – OOP-PFM histograms distribution of LiNbO3/Al2O3: 
curve 1 – LiNbO3/Al2O3 – @plus, curve 2 – LiNbO3/Al2O3 – 
@minus 
 
As can see from Fig. 4 (curve 1), for sample 
LiNbO3/Al2O3-@plus, the maximum of the OOP-PFM 
histogram of this distribution is shifted toward positive 
values of the piezoelectric response (~ 50), which implies 
that the polarization vector in most ferroelectric active 
grains is directed toward the lower interface. In 
contrast, for sample LiNbO3/Al2O3-@minus the 
maximum slightly shifted to negative value (~ – 10). 
The asymmetry of the distribution of the OOP-PFM 
signal is a manifestation of the so-called self-
polarization effect. The peaks “0” (zero piezoresponse) 
poses a signal from “non-ferroelectric” grains. 
Finally, remnant loops have been performed on the 
samples. Hysteresis in PFM is fundamentally different 
than hysteresis in a macroscopic sample. Macroscopic 
hysteresis occurs due to the nucleation growth and 
interaction of multiple separated domains, while in 
PFM, nucleation of a single domain occurs under a 
sharp tip and PFM signal follows the development of 
domains at a single location. Here, the remnant 
piezoresponse has been measured in 30 ms after the 
removal of the DC pulse (duration 30 ms).  
 
-80 -40 0 40 80
-300
-150
0
150
300
 
 
P
ie
zo
re
sp
o
n
se
, 
a
rb
. 
u
n
it
s
Voltage, V
 @minus
 @plus
 non-ferro
 
 
Fig. 5 – Remnant piezoelectric hysteresis loops of the 
LiNbO3/Al2O3 
 
An example of the resulting nanoscale piezoelectric 
hysteresis loops was measured in ferroelectric active 
areas of the both LiNbO3 thin films by applying cycles of 
80 V at the PFM tip, as shown in Fig. 5. The range of 
switching voltages was determined from the local 
piezoresponse hysteresis loops. The loop for 
sample LiNbO3/Al2O3-@plus is almost symmetrical and 
characterized the bigger remnant piezoelectric response 
(four times) compared with loop for LiNbO3/Al2O3-
@minus. On the other hand the coercive voltage for the 
sample LiNbO3/Al2O3-@minus is more then sample 
synthesized in positive electric field. The remnant PFM 
signal displayed a ferroelectric character in the LiNbO3 
thin film. Thus, we can suppose that the local hysteresis 
loop is caused by local domain switching underneath the 
tip. In contrast, for “non-ferroelectric” grains observed 
no switching in OOP-PFM signal in the entire range of 
DC voltage. 
 
4. CONCLUSIONS 
 
In summary, LiNbO3 ferroelectric films were grown 
on Al2O3 substrate by RF-magnetron sputtering in in-
situ electrical field different polarity. The films contain 
crystallites of LiNbO3 with preferable orientation [012] 
along the normal to the Al2O3 substrate surface [012] 
(Al2O3 and LiNbO3 have trigonal crystal system). 
Besides together with ferroelectric phase is formed non-
ferroelectric phase (as example LiNb3O8 particles). 
Deposition of lithium niobate films on a sapphire 
substrate under the action of electric field has a 
significant impact on their domain structure and 
ferroelectric properties. PFM was used to study vertical 
and lateral polarization direction in LiNbO3 thin films. 
The analysis of the histograms of vertical piezoresponse 
images allowed to reveal self-polarization effect in films. 
This effect is best shown for LiNbO3 film deposited in 
positive electric field. By this means even at low electric 
field intensity (~ 30 V/cm) during the synthesis observed 
a significant difference in OOP-PFM and IP-PFM 
signals for different polarity of the electric field – the 
presence of a large domain ordering at a positive 
potential on the substrate, and the almost complete lack 
of order at negative. Also, the local hysteresis loops are 
significantly different for samples grown at different 
 R.N. ZHUKOV, D.A. KISELEV, ET AL. J. NANO- ELECTRON. PHYS. 8, 04025 (2016) 
 
 
04025-4 
polarities of the electric field. 
From the results obtained in this paper, it follows 
that the choice of the crystallographic direction of the 
substrate and the synthesis of films under the action of 
a electric field can have a significant impact on their 
domain structure and ferroelectric properties. 
 
ACKNOWLEDGEMENT 
 
The studies are performed on the equipment of 
Center for Shared Use “Materials Science and 
Metallurgy” at the National University of Science and 
Technology “MISiS”. The research was financially 
supported by the Federal Target Program “Investigation 
and Engineering in High-Priority Lines of Development 
of Science and Technology in Russia for 2014‒2020” 
(unique project identifier RFMEFI57814X0071, contract 
no. 14.578.21.0071). 
 
 
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Synthesis and Nanoscale Characterization of LiNbO3 Thin Films Deposited on Al2O3 Substrate by RF Magnetron Sputtering under Electric Field

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Synthesis and Nanoscale Characterization of LiNbO3 Thin Films Deposited on Al2O3 Substrate by RF Magnetron Sputtering under Electric Field

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SocioEconomic Challenges Journal (Sumy State University)