Peculiarities and asymmetry of polarization reversal in Pt/PZT-film/Pt:Ti/SiO₂/Si-substrate structures in pyroelectric response investigations
By RF magnetron sputtering method the Pt/PZT-film/Pt:Ti-sublayer/SiO₂/Si-substrate structures were prepared and pyroelectric response amplitude and phase behaviour under external voltage application was investigated by photopyroelectric modulation method. The results of investigation of pyroelectri...
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
2004
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| Цитувати: | Peculiarities and asymmetry of polarization reversal in Pt/PZT-film/Pt:Ti/SiO₂/Si-substrate structures in pyroelectric response investigations / S.L. Bravina, E. Cattan, N.V. Morozovsky, D. Remiens // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2004. — Т. 7, № 3. — С. 263-271. — Бібліогр.: 27 назв. — англ. |
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Bravina, S.L. Cattan, E. Morozovsky, N.V. Remiens, D. 2017-06-04T15:58:22Z 2017-06-04T15:58:22Z 2004 Peculiarities and asymmetry of polarization reversal in Pt/PZT-film/Pt:Ti/SiO₂/Si-substrate structures in pyroelectric response investigations / S.L. Bravina, E. Cattan, N.V. Morozovsky, D. Remiens // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2004. — Т. 7, № 3. — С. 263-271. — Бібліогр.: 27 назв. — англ. 1560-8034 PACS: 78.20.-e https://nasplib.isofts.kiev.ua/handle/123456789/119121 By RF magnetron sputtering method the Pt/PZT-film/Pt:Ti-sublayer/SiO₂/Si-substrate structures were prepared and pyroelectric response amplitude and phase behaviour under external voltage application was investigated by photopyroelectric modulation method. The results of investigation of pyroelectric response – external voltage loops of polarization reversal, pyroelectric response – voltage poling curves and pyroelectric response – time repolarization curves and also dynamic current-voltage characteristics of Pt/PZT/Pt:Ti/SiO₂/Si-substrate structures are presented. From variation of pyroelectric response in the current and voltage modes the capacity-voltage loops of polarization reversal and poling curves were derived. From asymmetric pyroelectric response – time repolarization curves the voltage behaviour of characteristic times of zero response and saturation was analyzed. Observed transformations of current-voltage characteristics display the considerable voltage and time dependent variation of charge transfer conditions. The performed investigation has shown the strong correlation between the poling pyroelectric and so ferroelectric and electrical asymmetries. Presented data on the polar and time asymmetry of the conditions of polarization reversal are discussed in the terms of influence of dynamics of space charge asymmetry on pinning conditions under the different polarity of applied voltage in the course of polarization reversal. Authors gratefully acknowledge Ministry of Science of France and the University of Valenciennes for financial support. en Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України Semiconductor Physics Quantum Electronics & Optoelectronics Peculiarities and asymmetry of polarization reversal in Pt/PZT-film/Pt:Ti/SiO₂/Si-substrate structures in pyroelectric response investigations Article published earlier |
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| title |
Peculiarities and asymmetry of polarization reversal in Pt/PZT-film/Pt:Ti/SiO₂/Si-substrate structures in pyroelectric response investigations |
| spellingShingle |
Peculiarities and asymmetry of polarization reversal in Pt/PZT-film/Pt:Ti/SiO₂/Si-substrate structures in pyroelectric response investigations Bravina, S.L. Cattan, E. Morozovsky, N.V. Remiens, D. |
| title_short |
Peculiarities and asymmetry of polarization reversal in Pt/PZT-film/Pt:Ti/SiO₂/Si-substrate structures in pyroelectric response investigations |
| title_full |
Peculiarities and asymmetry of polarization reversal in Pt/PZT-film/Pt:Ti/SiO₂/Si-substrate structures in pyroelectric response investigations |
| title_fullStr |
Peculiarities and asymmetry of polarization reversal in Pt/PZT-film/Pt:Ti/SiO₂/Si-substrate structures in pyroelectric response investigations |
| title_full_unstemmed |
Peculiarities and asymmetry of polarization reversal in Pt/PZT-film/Pt:Ti/SiO₂/Si-substrate structures in pyroelectric response investigations |
| title_sort |
peculiarities and asymmetry of polarization reversal in pt/pzt-film/pt:ti/sio₂/si-substrate structures in pyroelectric response investigations |
| author |
Bravina, S.L. Cattan, E. Morozovsky, N.V. Remiens, D. |
| author_facet |
Bravina, S.L. Cattan, E. Morozovsky, N.V. Remiens, D. |
| publishDate |
2004 |
| language |
English |
| container_title |
Semiconductor Physics Quantum Electronics & Optoelectronics |
| publisher |
Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
| format |
Article |
| description |
By RF magnetron sputtering method the Pt/PZT-film/Pt:Ti-sublayer/SiO₂/Si-substrate structures were prepared and pyroelectric response amplitude and phase behaviour under external voltage application was investigated by photopyroelectric modulation method.
The results of investigation of pyroelectric response – external voltage loops of polarization reversal, pyroelectric response – voltage poling curves and pyroelectric response – time repolarization curves and also dynamic current-voltage characteristics of Pt/PZT/Pt:Ti/SiO₂/Si-substrate structures are presented.
From variation of pyroelectric response in the current and voltage modes the capacity-voltage loops of polarization reversal and poling curves were derived. From asymmetric pyroelectric response – time repolarization curves the voltage behaviour of characteristic times of zero response and saturation was analyzed. Observed transformations of current-voltage characteristics display the considerable voltage and time dependent variation of charge transfer conditions.
The performed investigation has shown the strong correlation between the poling pyroelectric and so ferroelectric and electrical asymmetries. Presented data on the polar and time asymmetry of the conditions of polarization reversal are discussed in the terms of influence of dynamics of space charge asymmetry on pinning conditions under the different polarity of applied voltage in the course of polarization reversal.
|
| issn |
1560-8034 |
| url |
https://nasplib.isofts.kiev.ua/handle/123456789/119121 |
| citation_txt |
Peculiarities and asymmetry of polarization reversal in Pt/PZT-film/Pt:Ti/SiO₂/Si-substrate structures in pyroelectric response investigations / S.L. Bravina, E. Cattan, N.V. Morozovsky, D. Remiens // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2004. — Т. 7, № 3. — С. 263-271. — Бібліогр.: 27 назв. — англ. |
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2025-11-24T15:47:04Z |
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2025-11-24T15:47:04Z |
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| fulltext |
263© 2004, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
Semiconductor Physics, Quantum Electronics & Optoelectronics. 2004. V. 7, N 3. P. 263-271.
PACS: 78.20.-e
Peculiarities and asymmetry of polarization reversal
in Pt/PZT-film/Pt:Ti/SiO2/Si-substrate structures
in pyroelectric response investigations
S.L. Bravina, E. Cattan*, N.V. Morozovsky, D. Remiens*
Institute of Physics NASU, 46, prospect Nauky, 03028 Kyiv, Ukraine
E-mail: bravina@iop.kiev.ua
* IEMN-DOAE- MIMM CNRS-UMR 8520, Universite de Valenciennes et du Hainaut- Cambresis,
9, Le Mont Houy, 59313 Valenciennes Cedex, France
E-mail: denis.remiens@univ.valenciennes.fr
Abstract. By RF magnetron sputtering method the Pt/PZT-film/Pt:Ti-sublayer/SiO2/Si-substrate
structures were prepared and pyroelectric response amplitude and phase behaviour under
external voltage application was investigated by photopyroelectric modulation method.
The results of investigation of pyroelectric response � external voltage loops of polarization
reversal, pyroelectric response � voltage poling curves and pyroelectric response � time repo-
larization curves and also dynamic current-voltage characteristics of Pt/PZT/Pt:Ti/SiO2/Si-
substrate structures are presented.
From variation of pyroelectric response in the current and voltage modes the capacity-voltage
loops of polarization reversal and poling curves were derived. From asymmetric pyroelectric
response � time repolarization curves the voltage behaviour of characteristic times of zero
response and saturation was analyzed. Observed transformations of current-voltage charac-
teristics display the considerable voltage and time dependent variation of charge transfer
conditions.
The performed investigation has shown the strong correlation between the poling pyroelectric
and so ferroelectric and electrical asymmetries. Presented data on the polar and time asymme-
try of the conditions of polarization reversal are discussed in the terms of influence of dynam-
ics of space charge asymmetry on pinning conditions under the different polarity of applied
voltage in the course of polarization reversal.
Keywords: PZT-film/Si structures, pyroelectric response hysteresis loops, polar and poling
asymmetry.
Paper received 20.05.04; accepted for publication 21.10.04.
1. Introduction
Polar PZT ceramics are known as materials with excel-
lent piezoelectric and pyroelectric properties [1, 2], which
are retained in PZT films [3, 4]. A good technological
compatibility with Si-base of modern electronics makes
PZT films be a leader in creation of elements of high-
density dynamic random access memories (DRAM�s),
non-volatile random access memories (NV-RAM�s), mi-
cro-electro-mechanics (MEM�s) and infrared sensorics
(IRS's) [3�5].
The practically important electrical characteristics
of �metal-PZT-film-metal on Si-substrate� system as those
of other systems of such type manifest the well-known set
of natural and technological asymmetries connected with
specificity of reversing the poling state in the electroded
ferroelectric film on the substrate [3�5].
The asymmetries of ferroelectric hysteresis loops and
current-voltage characteristics were found not only for
strongly asymmetric Au/PZT/Si heterojunction structures
[6] and also for weak asymmetric Ni/PZT/Pt/Si struc-
tures, which also possess the pyroelectric asymmetry [7].
Pyroelectricity is well known not only as important
applicable effect [2] but also as a high informative method
of the polar state investigation [8], especially when
pyroelectric response amplitude and phase behaviour was
investigated by photopyroelectric modulation method [8].
In this method the sample is investigated in the operation
modes of pyroelectric detector of radiation (PDR).
In this paper we present the results of investigations
of polar and poling asymmetries of the set of pyroelectric
264
SQO, 7(3), 2004
S.L. Bravina et al.: Peculiarities and asymmetry of polarization reversal in ...
characteristics of Pt/PZT-film/Pt:Ti/SiO2/Si-substrate
systems obtained by photopyroelectric modulation
method.
2. Experimental
2.1. Samples
The samples of PZT films were prepared by radio fre-
quency magnetron sputtering method on platinized
SiO2/Si substrate.
The bottom Pt:Ti-bilayer was formed by platinum
bottom electrode with a titanium adhesive layer (150 nm
of Pt and 10 nm of Ti) deposited on 350 nm SiO2 layer on
(100) n-type Si substrate.
For substrate stabilization the annealing treatment
of the Pt:TiOx/SiO2/Si-substrate structure just before of
PZT deposition was performed at 350�400°C. Then PZT
film was deposited on the bottom electrode. The sputter-
ing target obtained by uniaxially cold pressing includes
the mixture of PbO, TiO2 and ZrO2 in the stoichiometric
composition. The polar perovskite phase of the PZT-film
was obtained by post-annealing treatment at 600�650°Ñ
during 0,5�1 hour. The top Pt-electrodes were deposited
through a shadow mask by sputtering procedure, which
was followed by a lift-off, and have ≈1 mm2 of area. The
details of the sputtering conditions were described else-
where [9, 10].
The obtained PZT-films with Zr/Ti ratio 54/46 are
near the morphotropic phase boundary, which corre-
sponds to better performances for bulk PZT ceramics.
The thickness of the main components are the follow-
ing: 150 nm for the top Pt-electrode, 1.9 µm for layer for
PZT layer, 350 µm for Si substrate.
Each element has a current-carrying thin stripe with
a circle current electrode of 1 mm of diameter on the
stripe end.
2.2. Measurements
For the investigations of pyroelectric and ferroelectric
characteristics the measuring set for complete pyroelectric
and ferroelectric characterization [8] was used.
The measurements of amplitude Uπ and phase ϕπ of
pyroelectric response were carried out by photopyro-
electric modulation method in the current and voltage
modes. In the current mode Uπ = Uπ1 ∝ γ/c1, and in the
voltage mode Uπ = Uπ2 ∝ γ/c1ε⋅fm, (here γ is the pyroelect-
ric coefficient, c1 is the volume heat capacity, ε is the
dielectric permittivity, fm is the modulation frequency)
[2, 8]. Since Uπ1 ∝ γ and Uπ2 ∝ γ/ε, the dielectric ratio
Dπ = Uπ1/Uπ2 fm ∝ επ reflects the behaviour of dielectric
permittivity obtained by pyroelectric measurements.
Under examination of loops of pyroelectric response
hysteresis (Uπ -V-loops and ϕπ-V- loops) the Pt/PZT/Pt:Ti/
Si structure was investigated in the operating mode of
ferroelectric bolometer, at that applied d.c. voltage Vdc
was varied stepwise ±(0,25�1) V cyclically in the range
of �10 V ≤ Vdc ≤ +10 V. The same mode was used under
investigations of variations of transient pyroelectric re-
sponse in due course under application of d.c. voltage
(Uπ-t- and ϕπ-t- curves). The Uπ1,2-V-curves were obtained
after previous pulse depoling of the samples up to zero
response, which remains during a long period without
poling voltage application. The Uπ-t-curves were obtained
after previous 11 V d.c. poling of the samples up to satu-
rated Uπ value, which remains during a long period with-
out poling voltage application.
For minimization of polarization reversal contribu-
tion under dynamic current-voltage characterization
(I�V-curves) the unipolar saw-tooth drive voltage Vd with
0,5 s of durability and 1 Hz of repetitive frequency in the
amplitude range of 0 ≤ Vd ≤ 10 V was used.
During pyroelectric measurements the structure un-
der investigation was irradiated by modulated IR-probe
from IR LED supplied by generator of sinusoidal vol-
tage through the matching stage [8].
The matching stage for sensitive elements (SE) of
PDR, based on FET impedance transformer with using
dynamic load and changeable impedance in the input
circuit was applied [11, 12]. It successively operates in
the current mode (power measurement) and voltage mode
(energy measurement) in the range from infrasound up to
low ultrasound frequencies. So, the investigated Pt/PZT/
Pt:Ti/Si structures were placed in the conditions of op-
eration of the real SE of PDR.
3. Results and comments
3.1. Pyroelectric response characteristics
3.1.1. Pyroelectric response � modulation
frequency characteristics
The dependences Uπ1,2(fm) and ϕπ1,2(fm), obtained for the
investigated samples of Pt/PZT film/Pt:Ti/Si after posi-
tive (�+�) and negative (���) d.c. poling are presented in
Figures 1a and 1b.
The shapes of Uπ1,2(fm) and ϕπ1,2(fm) are near identi-
cal for �+� and ��� poled SE (compare Figs 1a and 1b).
Consecutive repolarization of SE gives 180°-addition to
ϕ1,2 which corresponds to the change of sign of pyro-
electric reaction of PZT film and only insignificant vari-
ations of shape of Uπ1,2(fm) and ϕπ1,2(fm) dependences.
This indicates the almost complete pyroelectric revers-
ibility of reorientation of polarization direction in inter-
electrode space of Pt/PZT/Pt:Ti structure. A small scat-
ter of Uπ1,2 values can be explained by the difference in
the degree of unipolarity of PZT film under the top Pt
electrode and the bottom Pt:Ti one.
3.1.2. Pyroelectric response � voltage poling
curves
Figure 1c presents the dependences of pyroelectric re-
sponse value on the poling voltages lower than the coer-
S.L. Bravina et al.: Peculiarities and asymmetry of polarization reversal in ...
265SQO, 7(3), 2004
cive ones and also near them. The application of the ex-
ternal d.c. voltage Vdc leads to the increase of Uπ1,2 from
zero to saturated values. These saturated values increase
with the increase of Vdc and remain during a long period
after getting off the Vdc of both negative and positive
polarities.
Obtained Uπ1,2-V-curves display the asymmetry of
positive and negative branches which consists in particu-
lar in positive shift of zero response regions and the breaks
in the vicinity of the threshold voltages Vth
±. Observed
threshold inequality of Uπ1,2-V-curves (Vth
� < Vth
+) corre-
sponds to the coercive inequality of Uπ1,2-V -loops (Vc
�<
< Vc
+) (see part 3.1.3).
For observed behaviour of ϕπ1,2-V-curves is charac-
teristic 180°-change of ϕπ1,2 under change of Vdc polar-
ity, which corresponds to the change of the sign of
pyroelectric reaction under polarization reversal.
Difference in Vth
� and Vth
+ values (Vth
� < Vth
+) are
visible under examination of the behavior of dielectric
ratio � voltage curves (Dπ-V-curves) (Figure 1c). Since
Dπ(Vdc) = Uπ1(Vdc)/Uπ2(Vdc) ∝ επ(Vdc) the Dπ(Vdc) depend-
ency reflects the behavior of επ(Vdc).
The tendency of changing Dπ(Vdc) observed on Dπ-V-
curves indicates the decrease of επ(Vdc) under Vdc in-
crease, which corresponds to decrease of the number of
domain walls in the film under poling. The peculiarities
of positive and negative branches of Dπ-V-curves around
of Vth
± are more diffused for Vth
� than for Vth
+. This re-
flects some differences in rearrangements of domain struc-
ture of the Pt/PZT film/Pt:Ti/SiO2/Si systems under dif-
ferent polarities of external voltage.
10
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Up1 /Up2 ⋅f
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10
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10
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Modulation frequency, Hz
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100
200
300
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0
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1
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2
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3
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4
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jp2
jp1
Modulation frequency, Hz
h
Fig. 1. Modulation frequency dependences (a, b) and poling
curves (c) of pyroelectric response amplitudes Uπ1,2(fm), dielec-
tric ratio Dπ = Uπ1/Uπ2 fm and phases ϕπ1,2(fm):
a � after +35 V, 5 min d.c. poling;
b � after �35 V, 5 min d.c. poling.
c � under d.c. poling after complete depoling.
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1400
1600
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2000
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Up1, µV
j
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266
SQO, 7(3), 2004
S.L. Bravina et al.: Peculiarities and asymmetry of polarization reversal in ...
3.1.3. Pyroelectric response � external voltage
poling � repoling loops
In Figures 2a and 2b the obtained loops of pyroelectric
response amplitude |Uπ1,2(Vdc)| and phase ϕπ1,2(Vd) and
also their combination into real signal Uπ1,2(Vdc) are pre-
sented.
The |Uπ1,2|-V-loops have the typical �butterfly�-like
shape, which is often observed for strain-electric field
response loops of PZT films [13].
The behaviour of |Uπ1,2(Vdc)| is characterized by the
regions of saturation at the front of the �wings� where
Vd > Vc and sharp changes with pronounced minima on
the �tails� of the �wings� in the vicinity of Vd = Vc.
The ϕπ1,2-V-loops have the characteristic parallelo-
gram-like shape with the regions of ϕπ1,2-change on 180°
in the vicinity of Vdc = Vc and ϕπ(Vdc) = const outside the
range of Vd = Vc.
Symmetry of the front parts of both positive and nega-
tive |Uπ1,2(Vdc)| � �wings� reflects the pyroelectric iden-
tity of both polarized states of investigated PZT film.
Asymmetry of the �tails� of the |Uπ1,2(Vdc)| � �wings� and
inequality Vc
� < Vc
+ indicates the difference on the ear-
lier stage of repolarization processes.
The shapes of obtained Uπ1,2-V-loops and inequa-
lity Vc
� < Vc
+ in general are similar to that known for
P-V-loops of metal/PZT-film/Si-substrate system [3, 4,
7, 9, 13].
The analysis of Uπ1-V-loops and Uπ2-V-loops shows
earlier and more complete saturation of Uπ1(Vdc) poling
curves comparatively with undersaturated Uπ2(Vdc) poling
curves for the both of Vdc polarities. Since Uπ1 ∝ γ and
Uπ2 ∝ γ/ε, we can conclude that the saturation of γ value
starts just before Vc
± and finishes just after Vc
±, which is
earlier than that of γ/ε value. So this is the ε value which
remains undersaturated under Vdc > Vc
±.
The behavior of dielectric ratio Dπ(Vdc) ∝ επ(Vdc) is
reflected by Dπ-V-loop presented in Figure 2c. Observed
asymmetry of Dπ-V-loop corresponds to the same of the
Uπ1,2(Vdc) -loops.
The general view of obtained Dπ(Vdc) changes under
poling-repoling cycle reflects the general tendency of
decreasing επ value in the poling run under Vdc increase
and conservation of lower value of επ under subsequent
decrease of Vdc. Also the step-like jumps of Dπ(Vdc) in
vicinity of Vdc = 0 with the maxima around of Vdc = 0 are
observed.
The sharp peculiarities of Dπ(Vdc) around of Vdc = Vc
are visible and the first one at Vc
+ is more pronounced
than the second one at Vc
�. These peculiarities of Dπ(Vd)
reflect the variations of επ(Vd) and so the states of the
domain structure of PZT film with the near zero unipo-
larity degree.
The behaviour of επ(Vdc) in the vicinity of Vdc = 0 and
Vdc = Vc
± can be connected with the peculiarities of rear-
rangement of domain structure of PZT film which con-
sists in mutual transformations of interconnected 180°-
and non-180°- (in particular, 90°-) domain groups [5, 14].
3.1.4. Pyroelectric response � time
repolarization transient curves
Figure 3 presents the changes of pyroelectric response
amplitude and phase in the course of repolarization of
Pt/PZT film/Pt:Ti structure by application of d.c. volt-
age Vdc less and near the coercive ones.
Under application of fixed external repoling d.c. volt-
age Vdc the decrease of Uπ value up to zero followed by
subsequent increase of Uπ value up to saturated one is
observed. This saturated value remains during a long
period after Vdc getting off.
Observed behaviour of ϕπ(t), namely 180°-change un-
der transition of Uπ(t) through its zero value, corresponds
to the change of the sign of pyroelectric reaction due to
polarization reversal in time induced by Vdc application.
For positive and for negative Vdc the similar tendency
in the Uπ(t) behaviour but at different time scales is ob-
served. So the strong asymmetry in the time scale of
repolarization process development is clearly evident.
Figure 4 presents repolarization transient curves Uπ(t)
combined from amplitude and phase time dependences
from Figure 3.
For positive and for negative poling voltages the re-
gions of Uπ(t) ~ Uπ(0)(1 � ηlog(t/τ)) are observed and the
slope η increase with Vdc value increase. For negative Vdc
on the both sides from zero response time the view of
Uπ(t) is different at low Vdc and similar at high Vdc. So
under negative Vdc the characteristics of domain walls
motion before and after repolarization are different at
low Vdc values and are similar at high Vdc values. For
positive Vdc on the both sides from zero response time the
slopes of Uπ(t) are different at both low and high Vdc. So,
under positive Vdc the characteristics of domain walls
motion before and after repolarization are different at
low and high Vdc values.
In Figure 5 the voltage dependences of zero-response
time t0 and saturation time ts are presented.
Increase of negative Vdc value leads to strong decrease
of ts and t0 values, which remain near constant when Vdc
value reaches and exceeds the Vc
� value. Under positive
Vdc value the same tendency of t0 changing but in more
narrow time scale is observed. At low Vdc the values of t0
are 1�2 orders of value higher at negative Vdc than at
positive ones but at high Vdc for the both polarities the
values of to are near the same. Under increase of negati-
ve Vdc the ts value decreases similar to t0 but under increa-
se of positive Vdc the ts value noticeably increases. So, for
negative Vdc the similar tendencies and for positive Vdc
the different tendencies in the behaviour of t0 and ts are
observed.
3.2. Dynamic unipolar current-voltage
characteristics
Figure 6 presents the set of dynamic unipolar current-
voltage characteristics obtained under different ampli-
tudes and polarities of drive voltage.
S.L. Bravina et al.: Peculiarities and asymmetry of polarization reversal in ...
267SQO, 7(3), 2004
In general, the structure of considered dynamic I�V-
curves is similar to those quasistatic ones observed for
many other electroded PZT-film based structures obtained
by different technologies [15�17]. On the I�V-curves ob-
tained at Vd < Vc can be distinguished three characteris-
tic regions. The first one at low Vd values is short and
jump-like and is connected with displacement current in
the moment of Vd rise. The second one at intermediate Vd
values is sub-linear. The third one at high Vd values is
super-linear.
The voltages Vt
� and Vt
+ of transition between sub-
linear and super-linear regions increase with increasing
Vd amplitude.
Comparison of the data in Figure 6 shows that the
differences of positive and negative branches which in-
crease with the rise of Vd values are rather high at short
times of Vd application and decrease after forming under
long term repetitive action of Vd saw-pulses. So observed
dynamic I�V-curves shows a pronounced dynamic char-
acter of polar asymmetry.
For unformed I�V-curves the development of super-
linear region with the rise of Vd is characteristic. The
forming during several minutes leads to the changes of
�15 �10 -5 0 5 10 15
0.1
1
10
100
20 Hz
a
P
y
ro
el
e
ct
r
ic
r
e
sp
o
n
se
A
m
p
li
tu
d
e
,
V
µ
U
U
p
p
2
1
�15 �10 -5 0 5 10 15
-100
0
100
200
300
V , V
=
P
h
a
se
,
d
eg
. jp2
jp1
�15 �10 -5 0 5 10 15
V , V=
�30
�20
�10
0
10
20
30
20 Hz
b
P
y
ro
e
le
c
tr
ic
r
e
sp
o
n
se
,
V
µ
Up2
�15 �10 -5 0 5 10 15
V ,V
=
�3
�2
�1
0
1
2
3
20 Hz
P
y
r
o
e
le
c
tr
ic
r
e
sp
o
n
se
,
V
µ
Up1
�15 �10 -5 0 5 10 15
1000
1200
1400
1600
1800
2000
D.c. voltage, V
D
ie
le
c
tr
ic
R
a
ti
o
,
a
r
b
.
u
n
it
s
20 Hz
c
=D Up p1 / U f ~ ⋅ e
p2
Fig. 2. Pyroelectric response � d.c. voltage loops:
a � �butterflies� of amplitudes Uπ1,2(V), and parallelograms of
phases 1,2(V);
b � hysteresis loops of responses Uπ2(V) (top) and Uπ1(V) (bot-
tom);
c � dielectric ratio Dπ(V) loop.
268
SQO, 7(3), 2004
S.L. Bravina et al.: Peculiarities and asymmetry of polarization reversal in ...
parameters of the I�V-curves. These changes are more
significant under increasing the drive voltage value (com-
pare the data in Figure 6). The expansion of sub-linear
region at the expense of super-linear one are observed.
Under Vd increase the slope of sub-linear region de-
creases. Under Vd > Vc the appearance of region with the
diffuse maximum and subsequent negative slope is char-
acteristic and more pronounced for the positive branch.
These regions are connected with currents of polariza-
tion reversal in the definite group of domains (�stubborn
domains�) which spontaneously return in the initial state
under Vd = 0. Taking into account the complex character
of mixed 90°- and 180°- domain structure in PZT films
[5] and the data [14] concerning the contribution of 180°-
and non-180°-domain groups into remanent polarization
in PZT films we can suppose that the stubborn domain
group in a significant degree consists of non-180°-do-
mains.
4. Discussion
The obtained results show that the investigated systems
possess polar asymmetry of pyroelectric parameters,
poling time and current-voltage characteristics, which
correspond to coexistence of interrelated ferroelectric
asymmetry and asymmetry of charge transport.
Indeed, processes of polarization reversal in the
Pt/PZT/Pt:Ti/TiO2/SiO2/Si structures are developed in
the condition of asymmetry of injection properties of Pt-
top and Pt:Ti-bottom contacts due to the difference in the
conditions of their manufacturing. Besides, there is an
asymmetry of profile of the space charge connected with
the profile of mobile and immobile point and expanded
defects. In PZT films these are VPb
+ and VO
� vacancies,
domain walls, boundaries of separate micro-regions of
PZT film, and also various types of distortions in under-
electrode regions of the film.
In the case of investigated Pt/PZT/Pt:Ti structures,
because of the complex configuration of the space charge,
the charge transport on the different stages of repo-
larization process can be realized by so called relay-
race alternation of different mechanisms (see their list in
Ref [17]). The complex structure of observed I�V-curves
and its changes in time are in accordance with this inter-
pretation.
Time, s
d.c. voltage:
+4 V
+4.5 V
+5 V
+6 V
10
0
10
10
1
1
10
10
2
2
10
10
3
3
10
10
4
4
10
10
5
5
0.0 0.0
0.5 0.5
1.0 1.0
1.5 1.5
2.0 2.0
2.5 2.520 Hz
d.c. voltage:
�4 V
�4.5 V
�4.75 V
�5 V
�5.5 V
�6 V
10
10
5
5
10
10
4
4
10
10
3
3
10
10
2
2
10
10
1
1
10
10 10
0
0 0
�100 �100
0 0
100 100
200 200
P
h
a
se
,
d
e
g
.
P
y
ro
el
ec
tr
ic
r
e
sp
o
n
se
A
m
p
li
tu
d
e
,
V
µ
Fig. 3. Pyroelectric response amplitude-time and phase-time
repolarization curves: top � pyroelectric response amplitude;
bottom � pyroelectric response phase; left � for negative d. c.
voltages; right � for positive d. c. voltages.
Time, s
10
0
10
1
10
2
10
3
10
4
10
5
10
5
10
4
10
3
10
2
10
1
10
0
P
y
ro
e
le
ct
ri
c
re
sp
o
n
se
A
m
p
li
tu
d
e
,
V
µ
d.c. voltage:
+4 V
+4.5 V
+5 V
+6 V
�2 �2
�1 �1
0 0
1 1
2 2
3 3
20 Hzd.c. voltage:
�4 V
�4.5 V
�4.75 V
�5 V
�5.5 V
�6 V
Fig. 4. Pyroelectric response signal � time repolarization tran-
sient curves: left � for negative d. c. voltages; right � for positive
d. c. voltages.
�7 �6 �5 �4 �3
10 100 0
10 101 1
10 102 2
10 103 3
10 104 4
Voltage, V
C
h
a
r
a
ct
e
r
is
ti
c
ti
m
e
s,
s
3 4 5 6 7
t
s
t
o
Fig. 5. Voltage dependences of pyroelectric response charac-
teristic times under d. c. voltage repolarization: left � for nega-
tive d. c. voltages: right � for positive d. c. voltages.
S.L. Bravina et al.: Peculiarities and asymmetry of polarization reversal in ...
269SQO, 7(3), 2004
�2 �1 0 1 2
�15
�10
�5
0
5
10
15
1 Hz saw
pulses
10 s
1�3 min
Current density,
µA/cm2
Voltage, V
�60
�40
�20
0
20
40
60
1 Hz saw
pulses
Voltage, V
�6 �3 0 3 6
10 s
2-3 min
Current density,
µA/cm2
�8 �4 0 4 8
�80
�60
�40
�20
0
20
40
60
1 Hz saw
pulses
10 s
1 min
3 min
Voltage ,V
Current density,
µA/cm2
�80
�100
�60
�40
�20
0
20
40
60
1 Hz saw
pulses
Voltage ,V
�10 �5 0 5 10
10 s
1 min
3 min
Current density,
µA/cm2
Fig. 6. Dynamic unipolar current-voltage characteristics under different drive voltage amplitudes.
270
SQO, 7(3), 2004
S.L. Bravina et al.: Peculiarities and asymmetry of polarization reversal in ...
A super-linear region of I�V curves is usually associ-
ated with enrichment with charge carriers of near-con-
tact region with metal and discussed in terms of injection
mechanisms connected with the existence of currents lim-
ited by space charge [18], Schottky emission [19] and
Pool-Frenkel ionization [20]. A sub-linear region of I-V-
curves can be connected with depletion of contacting re-
gions of essentially different degree of doping due to ex-
clusion and extraction of charge carriers [21]). The for-
mation of such structure is characteristic for the case of
diffusion of metal in semiconductor in the region of their
contact as the result of thermal treatment and is quite
possible in the course of manufacturing the investigated
Pt/PZT/Pt:Ti structures.
Dynamic character of observed current asymmetry
points to the change of conditions of charge transport
with time. So, the observed pyroelectric asymmetry is
developed in the conditions of changing the space charge
profile with time.
The changes of pyroelectric response under reversing
polarization are connected with domain structure recon-
struction. That is why the time of such changes is deter-
mined in a high degree with processes of nucleation of
new domains and displacement of domain walls.
The peculiarities of domain structure behaviour un-
der polarization direction reversal in the perovskite crys-
talline ferroelectrics [22] and in PZT films [5, 14, 23] are
similar in many details. For initially non-polarized or
depolarized crystals and PZT films, contained a number
of disordered domains of non-180°- (in particular, 90°-)
and 180°- orientation the polarization process occurs
under action of external voltage by simultaneous displace-
ment of non-180°- and 180°- domain boundaries, and
reorientation of 180°-domains. The process of polariza-
tion reversal in PZT films starts from the nucleation and
growth of opposite domains (OD) of wedge-like shape
from the surface into the depth of the film and finishes by
broadening the domains spreading through the film by
side displacement of domain walls (DW).
The role of processes of charge transport under po-
larization reversal in thin layer structures of metal-
ferroelectric-metal type by means of formation OD and
displacement of charged DW was considered earlier in
[24, 25]. Facilitation of the conditions of domain nuclea-
tion and growth in film structures due to presence of di-
electric non-uniformity was considered recently in [26,
27]. To provide the displacement of charged DW it is
necessary to supply the certain value of mobile electric
charges, which is necessary for compensation of change-
able bounded charge. The peculiarities of this DW dis-
placement define the peculiarities of Uπ-V- and Uπ-t-
curves.
Under registration of Uπ-V- poling curves the increase
of Uπ(Vdc) from zero value to the maximal one at given
Vdñ value starts in the system of mutually pyroelectrically
compensated ÎD and occurs in the system of rearranged
ÎD. At that the value Vdñ = Vth corresponds to the begin-
ning of sharp change of Uπ under Vdñ increase and so the
start of fast rearrangement in the system of OD.
Under registration of Uπ-t-curves of repolarization
the variation of Uπ(t) reflects the trend of compensation
process in the preliminary arranged OD system. The
moment t = t0 when Uπ(t0) = 0 corresponds to pyro-
electrically compensated state of OD system. So the time
t = t0 corresponds to transport of such value of electrical
charge, which is necessary for creation of number of ÎD
required for compensation.
The fact of vanishing Uπ values at Vd = Vc
± under Uπ-
V-loops cycling and also at t = t0
± under Uπ-t-curves re-
gistration permits to consider some analogies between
the coercive voltages Vc
± and zero response times t0
±.
Starting from the definition of the effective degree of
unipolarity ξ = (ñ+ � ñ�)/(ñ+ + ñ�), where ñ+ and ñ� are the
concentrations of the domains with the opposite direc-
tions of the components of polarization vector Ps along
the thickness of the film, we can conclude that at Vd = Vc
±
and at t = t0
± the value ξ = 0. Since the values Vd = Vc
±
and t = t0
± correspond to the similar states of the domain
structure, namely those just balanced between two in-
versely poled states, we can consider t0 as the coercive
times. Indeed, from the standpoint of transport of charge
value necessary for vanishing the value of integral po-
larization, the coercive voltage is the necessary voltage
value under given time of its action, and the coercive time
is the necessary time under given voltage value.
5. Conclusions
The performed investigation has shown the strong corre-
lation between the poling pyroelectric and so ferroelectric
and electrical asymmetries.
Observed behaviour of Uπ-V- and Uπ-t-curves and also
Uπ-V-loops displays the considerable polar and time
asymmetry of polarization reversal.
Observed transformation of I�V-curves is the evidence
of considerable V- and t- dependent variation of charge
transport conditions.
Changes of pinning conditions, domain wall motion
characteristics, charge and mechanical state of the point
(immobile and mobile) and extended (domain wall) de-
fects is the reason of observed complex asymmetry.
For the investigated PZT thin films on Si systems with
complex composition and asymmetric space charge pro-
file is characteristic its change with time under the action
of applied external voltage.
The consequence of contact asymmetry and space
charge asymmetry is the difference in the conditions of
electric charge transport under the different polarity of
applied voltage. It results, in particular, in different time
of space charge accumulation necessary for reversing the
polarization direction and also in different spread of this
process in time. It leads to the difference in coercive times
for Uπ-t-curves obtained under different polarity of poling
voltage, and also to the difference in coercive voltage
values obtained for Uπ1-V- and Uπ2-V-loops under differ-
ent polarity of drive voltage.
For as more complete as possible examination of po-
larization reversal processes in PZT thin films on Si struc-
S.L. Bravina et al.: Peculiarities and asymmetry of polarization reversal in ...
271SQO, 7(3), 2004
tures it is necessary to perform the investigation of the
complex of their electrophysical characteristics includ-
ing not only ferroelectric but at the least pyroelectric and
current-voltage characteristics.
Acknowledgements
Authors gratefully acknowledge Ministry of Science of
France and the University of Valenciennes for financial
support.
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