Transcript Ferroelectric nanomaterials for electronic technique

Ferroelectric nanomaterials for
electronic technique
M. D. Glinchuk
Institute for Problems of Materials Science
National Academy of Sciences of Ukraine
Kiev, Ukraine
E-mail: [email protected]
I. Main fields of ferroelectric materials application
in electronic technique
• capacitors
• piezoelectric devices (ultrasound sources, resonators, filters,
phones, microphones, piezotransformators etc.)
• radiolocation and communication systems (the devices on surface
acoustic waves, waveguides, coders and decoders etc.)
• devices for night vision, high harmonic generation
• systems for recording and reading of information
• piezoelectric devices, heat-visioners for medicine and biology
• posistors for the systems of thermal regime control
II. Anomalous properties near the phase
transitions as the basis for applications
Giant dielectric permittivity of relaxor
ferroelectric (Pb,La)TiO3 [B.-G. Kim et
Temperature dependence of electrical
resistance of (Ba,Sr)TiO3:Y3+:Nb5+ ceramics
al., Phys. Rev. Lett. 86, 3404 (2001)]
[Z. He et al., J. Phys.:Cond. Matter 16, 6961 (2004)]
Shortcomings of bulk ferroelectrics: strong dependence of the properties on
temperature and scattering of phase transition temperatures while for application we
mostly need room temperature; the necessity for integration with semiconductors
and metals; the demands for the devices miniaturization; the materials, energy and
money savings.
All these shortcomings can be overcome in the nanomaterials.
III. Size effects of ferroelectric nanomaterials properties
Size dependence of the transition
temperature from ferroelectric (FE)
to paraelectric (PE) phase
Powder BaTiO3
400
Glinchuk M.D.,
Eliseev E.A.,
Stephanovich V.A.,
J. Appl. Phys., 93(2),
1150 (2003); Physica
B, 332, 356 (2002)
Glinchuk M.D.,
Morozovska A.N.,
Phys. Stat. Sol., 238,
81 (2003)
5000
4000
3000
2000
Powder BaTiO3
FE
Powder PbTiO3
380
Temperature T, K
Dielectric permittivity
6000
360
800
PE
T, K
Dependence of dielectric permittivity
on nanoparticles mean sizes
340
320
PE
750
FE
700
300
0
10
20
0.1
30
40
50
d, nm
1000
1
0.1
10
Radius r, m
Diameter d, m
Powder PbTiO3
Powder PbTiO3
E. Erdem et al.,
J. Phys.: Condens.
Matter 18, 3861
(2006)
1
10
III. Size effects of ferroelectric nanomaterials
properties
The physical background of the properties size effects, including size-driven
ferroelectric–paraelectric phase transition is the influence of surface which
can not be neglected at nanosizes. The main peculiarities is the appearance
of the properties gradients and so their inhomogeneity, the influence of
mechanical conditions on the surface (confinement conditions) and the
essential contribution of depolarization field. As the result the new properties
absent in bulk materials appear in ferroelectric nanos.
In what follows I will demonstrate some of the new properties.
IV. New phases originated from mechanical
conditions on the surface of ferroelectric thin films
PbTiO3 film on SrTiO3 substrate
Electret
800
Self-polarized
ferroelectric phase
600
400
200
0
0
5
10
15
20
25
30
Film thickness h (lattice constants)
1.07
Tetragonality c/a
Temperature T (K)
1000
PbTiO3 film on SrTiO3: Nb substrate
Um<0
1.06
Um=0
1.05
1.04
hcr
1.03
0
100
200
300
400
500
Film thickness h (A0)
The deformation of the film due to mismatch between the parameters of the film and substrate
Um = (b – a)/b (a, b are their lattice constants) and the surface piezoelectric effect induce builtin electric field. This field lead to electret state in the thinnest film. With the thickness increase
the self-polarized ferroelectric phase appears. The phenomenon of self-polarization is very
useful for the films application e.g. in pyroelectric devices because it allows to omit the costly
process of polarization by external field. Ferroelectric phase can be conserved in the thinnest
film (up to monolayer) by special choice of the pair film–substrate.
Glinchuk M.D., Morozovska A.N., Eliseev E.A., J. Appl. Phys. 99, 114102 (2006)
Glinchuk M.D., Morozovska A.N., J. Phys.: Cond. Matter 16, 3517 (2004)
Eliseev E.A., Glinchuk M.D., Phys. Stat. Sol. (b) 241, R52 (2004)
Glinchuk M.D., Morozovska A.N., Eliseev E.A., Integrated Ferroelectrics, 64, 17 (2005)
V. Conservation and enhancement of ferroelectric
properties in nanotubes and nanowires
Scheme of perovskite structure
deformation under external pressure
Effective piezoresponse of PbZr0.52Ti0.48O3
nanotube (outer diameter 700 nm, thickness
of wall 90 nm, the length about 30 mm) in
dependence on applied voltage. Symbols –
experimental data; solid line – theory.
Pressure on lateral surface of nanowire due to surface tension enhances the polar
properties of nanos
A.N.Morozovska, E.A.Eliseev and M.D. Glinchuk, Phys. Rev. B. 73, 214106 (2006)
V. Conservation and enhancement of ferroelectric properties
in nanotubes and nanowires
Nanorods of сегнетової
Rochel salt солі
(RS)(RS)
Наностержні
r = r=30nm,
30 nm, l =
500 nm
l=500nm
electricity
enhancement
RS
Decomposition
Ferro-
Remanent polarization PSV dependence on
temperature and hysteresis loop for RS nanorods
with radius 15 nm.
Symbols – experimental data; solid lines – theory.
D. Yadlovker and S. Berger,
Phys. Rev. B 71, 184112 (2005)
0.15
2
PSV
1
P (C/cm2)
Tr > T C
Decomposition
RS
Bulk transition
temperature TC
PSV (C/cm2)
0.3
0
-1
-2
0
20
40
60
ТСb
Temperature (С0)
-100
-50
0
50
E0 (kV/cm)
A.N.Morozovska, E.A.Eliseev and M.D. Glinchuk, Phys. Rev. B. 76, 014102 (2007)
100
V. Conservation and enhancement of ferroelectric properties
in nanotubes and nanowires
Nanorods
Nanotubes with walls of
different thickness
Effective surface tension and decrease of depolarizaton field
on cylindrical surface are the reasons of ferroelectric
properties enhancement in nanorods and nanotubes of
perovskite (Q12 < 0) ferroelectrics. This effect is very useful
for development of new nanomaterials with high polar
properties (better than in bulk).
A.N. Morozovska, E.A Eliseev and M.D. Glinchuk,
Physica B, 387, 358 (2007); Phase Transitions 80, 71 (2007)
VI. Phase states and giant magnetoelectric effect
induced by surface tension in ferroic nanoparticles
• Ferroelectric phase has to appear at room temperature in nanorods and
nanowires with r  50 nm of incipient ferroelectrics, which conserve
paraelectric phase up to 0 K in bulk. The existence of ferroelectric phase at
room temperature will be useful for development of new generation of the
devices on the basis of nanostructures.
• The ferromagnetic phase observed in spherical nanoparticles with radius
7–30 nm at room temperature of nonmagnetic in bulk materials CeO2, Al2O3,
ZnO, SnO2 etc. (Phys. Rev. B 74, 161306(R) (2006)) can be induced by
surface tension that increases inversely proportional to the particle radius.
• The giant magnetoelectric coupling which increase dielectric tunability about
two orders of magnitude was predicted in multiferroic nanorods due to surface
tension influence. The phenomenon is very important for application because it
will allow to write information by electric field and read it by magnetic field.
A.N.Morozovska, E.A.Eliseev and M.D. Glinchuk, Phys. Rev. B 76, 014102 (2007)
M.D. Glinchuk, E.A.Eliseev, A.N.Morozovska and R.Blinc, Phys. Rev. B 77, 024106 (2008)
VII. Electronic technique devices for nowadays or
nearest future applications
1. Pyroelectric infrared sensors on the basis of thin (from tens to hundreds nm)
ferroelectric films PbZr0.5Ti0.5O3 on the Si–SiO2 substrates, which are generating electric
current at temperature changing (e.g. due to infrared irradiation) are widely used as the
detectors sensing the living organisms presence (frequently nonwanted), sensing the
temperature enhancement under the fire beginning and producing the alarm signals; they
are useful also for medical examination of humans health. Nowadays there is multimillion
production of pyrosensors and transducers in Simens, Marconni, Muratta etc. The
important advantage of thin ferroelectric films is their self-polarization, its nature being
found out by us.
VII. Electronic technique devices for nowadays or nearest
future applications
2. The ferroelectric devices for an information recording. The concept of recording is the
polarization PS  0 and PS = 0 corresponds respectively to 1 and 0 (binary system), i.e. it is
related to the switching of polarization. The coercive field in the bulk ferroelectrics is about
several kV/cm, while semiconductor devices in the integrated scheme are working at a few
V/cm. Because of this it is necessary to use thin films, where the coercive field is small
enough. In comparison with magnetic films ferroelectric ones have the advantage of larger
memory, of energy saving, of higher rate of information exchange e.g. in mobile phones,
photocameras, videocameras etc. In these important consumer equipment many ferroelectric
capacitors are use to provide the work of the devices on necessary frequencies.
The main problem of ferroelectric memory is the process of reading related to
depolarization current, that lead to the film deterioration with time. Contrary in the magnetic
films the information recording process can destruct the film. Because of this the scientists
and engineers are discussing now the possibility to use multiferroics, i.e. the materials with
coexistence of ferroelectric and ferromagnetic order with strong magnetoelectric coupling,
so that an information can be recorded with the help of electric field and can be read with
the help of magnetic field. It was mentioned earlier that such possibility can occur in
nanoparticles as our calculations had shown. Many firms in all the world (Toshiba,
Samsung, Integrated Semiconductors, Matsushita etc.) are working on the problems related
to the production of improved ferroelectric films for memory devices.
VII. Electronic technique devices for nowadays or nearest
future applications
3. Other applications
Nanoparticles and
nanocomposites (sphere,
tubes, rods, wires)
Applications
Profiled nanostructures
(nanodomains, superlattices)
Optical generators of higher
Micro- and nano-electromechanical
Pyroelectric detectors.
harmonics, transducers,
systems. Energy transducers and
Three-dimention
frequency converters,
accumulators. Long-term memory
architecture of ferroelectric
parametric amplifiers. Memory memory. Photon devices.
elements on the basis of thin films.
Multielemental piezo- and pyrosensors. systems of new generation. Electrooptical and nonlinear
Ferroelectric micro- and
Optical devices
optical devices. New
nanolithography
generation of printers
Advantages
Nanofilms and their multilayers
(epitaxial, textured, polycrystalline)
Space-saving, integrability with modern Enlargement of spectral region,
semiconductor devices, the decrease of
controlling of angular
3
manipulated voltage in 10–10 times.
dependence. Increase of
High density of information recording, recording density, enhancement
minor time of access. Development of of stability. High decoupling
ferroelectric nanos with new properties
ability
in comparison with bulk materials
Enlargement of sensitivity.
High density of information
recording. Improvement of
quality factors, cost decrease
Conclusions
• In the system nanofilm–substrate the choice of substrate can essentially influence the
film phase diagram and properties, namely:
For compressed films self-polarized ferroelectric state can be conserved up to several
lattice constants thickness. Self-polarized films are very useful for the development of
high-quality pyrosensors and modern memory systems.
For stretched films built-in electric field originated from the mechanical stress in the
system nanofilm–substrate induces elektret-like polar state. Its properties can be useful in
construction of pyroelectric detectors and actuators without hysteresis.
• The possibility to obtain giant dielectric permittivity (from 105 to 106) is shown in
multilayers of thin films relaxor ferroelectric–paraelectric, which is important for
development of space-saving capacitors of new generation.
• The enhancement of ferroelectric properties in the cylindrical nanoparticles (rods, wires,
tubes) of ferroelectrics with perovskite structure arises due to surface tension on the lateral
surface and to the decrease of depolarization field for cylindrical geometry. Array of
cylindrical nanoparticles can be used for the creation of modern memory systems,
pyroelectric detectors.
• It was shown for the first time that surface tension which increase at nanoparticle radius
decrease can lead to the appearance of ferroelectric or/and magnetic state with giant
magnetoelectric effect in nanoparticles with radius smaller than 50 nm. This effect will be
useful to control the work of the devices both by electric or magnetic field.
Thank you for attention