Ferroelectrics Material Aspects Part 9 doc

2001 Microstructural, dielectric and ferroelectric properties of calcium-modified lead titanate thin films derived by chemical processes, J.. 2006 Effect of electrical conductivity on po

Lead Titanate-Based Nanocomposite:Fabrication,

Characterization and Application and Energy Conversion Evaluation 269 Within this context, four square composite samples with 4.5 cm2 were poled with suitable electric field and copper foil (1 mm thick) was glued for electrical contact as show in Figure

12 Table 3 shows the longitudinal d33piezoelectric coefficient for each one

To evaluate the power generated by these samples, they were pressed by the blue car continuosly as shown in Figure 13 The weight and the frequency of the blue car which will impact the composite samples can be controlled and fixed during the experiment The output voltage provided by the piezoelectric composite can be measured with an oscilloscope

Fig 13 System used to simulate the vehicle traffic or people walking

A track is project and constructed with two parts A bottom steel base with electrical tape on its top, fixed to a press device plane A top made of aluminum with the bottom with duct tape, and attached to external screws that make this part of mobile resource, since the composite is between bottoms and top part of the track it receives the impact of the track above it The composites were used as transducer individually, in series and in parallel Then they were connected directly (open circuit) to acquire the waveforms from the digital oscilloscope Further, the composites were connected in circuit (closed circuit) with the oscilloscope at the entrance acquiring waveforms again Finally, voltages were measured at the capacitors for every minute during 10 minutes Acquisition board was used to get the electrical signal provided by the composite This board consists of a retifier circuit AC/DC and a output capacitor

The experiments starts using a force of 200 kgf, to stroke the composites with a frequency of 3.0 Hz, and a capacitor of 3300 μF The open circuit (directly on the composites) and the

Ferroelectrics – Material Aspects

Lead Titanate-Based Nanocomposite:Fabrication,

Characterization and Application and Energy Conversion Evaluation 271

Experimental results show that an open circuit output voltage of 17.0 Vpp are generated

while in closed circuit the peak to peak voltage generated is 2.13 V because of the

impedance of the capacitor

Figure 15 shows the energy analysis of the experiments for different configurations of the

composite films It can be seen the increasing energy supplied when the composite films are

connected in parallel The useful energy, after 10 min, by four composite films is about ten

times higher than the energy generated by one composite film The values of energy in

Figure 15 were calculated from the measurement of the output voltage against time, using

the following relation:

212

where U is the available energy and V is the voltage measured on the capacitor The voltage

was measured during the charge of the capacitor due to the deformation of the composite

films by the applied stress

5 Conclusions

Composite films made of PZT ceramic immersed in PVDF polymer matrix were obtained

with 0-3 connectivity The method of synthesis can provide different structure of the

ceramic and also can provide ceramic particles with different size distribution which are

important parameters for the electroactive properties of the sample The inclusion of a

semiconductor phase, separately or coating the ceramic particles improve the poling

process of the composite, avoiding timing consuming and high applied electric field to

polarize the ferroelectric ceramic particles immerse into the polymer matrix The

advantages of recovered particles is the better control of the homogeneity of the particle

distribution avoiding percolation of conductive particles that may form a continuous path

which not allow the poling process

Using small amount of ceramic (30 vol%) the composite was used as infrared detector,

indicating the possibility of its use as intruder detector or fire alarm Using the right

protonation (doping) degree of the PAni, the composite display piezo and pyroelectric

coefficients high as many composite materials with higher ceramic content even when poled

with lower electric field and shorter poling time The study of energy harvesting simulating

people walking or vehicle traffic showed low power generated by each small composite

sample (4.5 cm2 area) but the association of four samples enhanced the converted electrical

energy from the energy wasted during vehicle traffic These preliminary results show that

the composite material deserves to be deeply studied as alternative material to obtain clean

energy

6 Acknowledgment

This work has financial support from the Brazilian Agencies: Fundação de Amparo à

Pesquisa do Estado de São Paulo – FAPESP and Conselho Nacional de Desenvolvimento

Científico e Tecnológico – CNPq through the Instituto Nacional de Ciência e Tecnologia de

Materiais em Nanotecnologia – INCTMN

Ferroelectrics – Material Aspects

272

7 References

Abothu, I R.; et al (1999) Processing of Pb(Zr0.52Ti0.48)O3 (PZT) ceramics from microwave

and conventional hydrothermal powders Materials Research Bulletin, 34, (9), 1411–

1419

Anton, S R & Sodano, H A (2007) A review of power harvesting using piezoelectric

materials (2003 – 2006), Smart Mater Struct., 16, R1 – R21

Bauer, F (2000) PVDF shock sensors: applications to polar materials and high explosives,

IEEE Trans Ultrason Ferroelectr Freq Control, 47 (6), 1448 -1454

Blinova, N V., et al (2008) Control of polyaniline conductivity and contact angles by partial

protonation, Polym Int 57, 66 – 69

Boumchedda, K., Hamadi & M., Fantozzi, G (2007) Properties of a hydrophone produced

with porous PZT ceramic, J European Ceram Soc., 27, 4169 – 4171

Brown L F.& Mason, J L (1996) Disposable PVDF Ultrasonic Transducers for

Nondestructive Testing Applications, IEEE Trans Ultrason Ferroelectr Freq Control,

43 (4), 560 – 567

Chang, L (2002) Wind energy conversion systems, IEEE Canadian Review –Spring/Printemps,

12 – 16

Chau, K H., Wong, Y W., & Shin, F G (2007) Enhancement of piezoelectric and

pyroelectric properties of composite films using polymer electrolyte matrix, Appl Phys Lett., 91, 252910

Chu, S-Y.& Chen, T-Y (2004) Fabrication of modified lead titanate piezoceramics with zero

temperature coefficient and its application on SAW devices, IEEE Trans Ultras Ferroelctr Freq Contr., 51 (6), 663 – 667

Ciang, C C., Lee, J-R.& Bang, H-J (2008) Structural health monitoring for a wind turbine

system: a review of damage detection methods, Meas Sci Technol 19, 122001 Das-Gupta, D K (1999) Ferroelectric composite sensor materials, Mater Eng., 10 (2), 97 –

125

De Carvalho, A A & Alter, A J (1997) Measurement of X-ray intensity in the medical

diagnostic range by a ferroelectric detector, Ultrason Ferroelectr Freq Control, 44 (6),

1198 – 1203

De Paula, M H., et al (2005) Microcontrolled pyroelectric instrument for measuring X-ray

intensity in mammography, Med, Biol Eng Comput., 43, 751 – 755

Dias, C J.& Das-Gupta, D K (1996) Inorganic ceramic/polymer ferroelectric composite

electrets, IEEE Trans Dielectr Electr Insul., 3 (5), 706 – 734

Dutta, P.K., et al (1994) Hydrothermal Synthesis and Dielectric Properties of Tetragonal

BaTiO3, Chem Mater., 6 (9):1542-1548

Edwards, G., et al (2006) PMN-PT single-crystal transducer for non-destructive evaluation,

Sensors and Actuators A, 132, 434 – 440

Estevam, G P., De Melo, W L B & Sakamoto, W K (2011) Photopyroelectric response of

PTCa/PEEK composite, Review of Scientific Instruments, 82, 023903

Feng Y., et al (2010) A model for 0-3 piezoelectric composites with an interlayer, Polymer

Composites, 1922 – 1927

Furukawa, T., Fujino, K & Fukada, E (1976) Electromechanical properties in the composites

of epoxy resin and PZT ceramics, Jpn J Appl Phys 15 (11), 2119 – 2129

Lead Titanate-Based Nanocomposite:Fabrication,

Characterization and Application and Energy Conversion Evaluation 273 Furukawa, T., Suzuki, K & Date, M (1986) Switching process in composite systems of PZT

ceramics and polymers, Ferroelectrics, 68, 33 – 44

Guggilla, P et al (2006) Pyroelectric ceramics for infrared detection applications, Materials

Ishikawa, K., et al (1994) Crystallization and growth process of lead titanate fine particles

from alkoxide-prepared powders, Jpn J Appl Phys 33, 3495

Jaffe, H., Piezoelectric applications of ferroelectrics, IEEE Trans Electr Devices, 16 (6), 544 –

554 (1969)

Kawai, H (1969) The piezoelectricity of poly(vinylidene fluoride), Jpn J Appl Phys., 8, 975 –

976

Klee, M et al (2010) Ferroelectric and piezoelectric thin films and their applications for

integrated capacitors, piezoelectric ultrasound transducers and piezoelectric

switches, IOP Conf Series: Mater Sci and Eng 8, 012008

Koyama, D & Nakamura, K (2009) Array configurations for higher power generation in

piezoelectric energy harvesting, IEEE International Ultrasonics Symposium Proceedings, 1973 – 1976

Kumar N & Nath, R (2005) Ferroelectric phase stability studies in potassium nitrate:

Polyvinylidene fluoride composite films, J Appl Phys., 97, 024105

Lau, S T., et al (2002) Piezoelectric composite hydrophone array, Sensors and Actuators A,

96, 14 – 20

Lau, S T., et al (2007) A poling study of lead zirconate titanate/polyurethane 0-3

composites, J Appl Phys., 102, 044104

Lencka, M.M & Riman, R E (1995) Thermodynamics of the Hydrothermal Synthesis of

Calcium Titanate with Reference to Other Alkaline-Earth Titanates, Chem Mater., 7:

18-25

Liu, X-F., et al (2006) Piezoelectric and dielectric properties of PZT/PVC and graphite

doped with PZT/PVC composites, Mater Sci Eng B, 127, 261 – 266

Lovinger, A (1982) Developments in Crystalline Polymers-1, D C Basset Ed., Applied Science

Publishers, 195 – 273 London

Lovinger, A (1983) Ferroelectric Polymers, Science, 220, 1115 – 1121

Luo, Z., et al (2008) Self-assembly of BaMoO4 single-crystalline nanosheets into

microspheres, Materials Chemistry and Physics, 110, 17- 20

Mandelis, A & Zver, M M (1985) Theory of photopyroelectric spectroscopy of solids, J

Appl Phys., 57 (9), 4421 – 4430

Marin-Franch, P., et al (2002) PTCa/PEKK piezo-composites for acoustic emission

detection, Sensors and Actuators A, 99 236 – 243

Moreira, M L., et al (2009) Synthesis of Fine Micro-sized BaZrO3 Powders Based on a

Decaoctahedron Shape by the Microwave-Assisted Hydrothermal Method, Crystal Growth & Design, 833-839

Ferroelectrics – Material Aspects

274

Morita, T (2010) Piezoelectric Materials Synthesized by the Hydrothermal Method and

Their Applications, Materials, 3, 5236 – 5245

Muralt, P.& Baborowski, J (2004) Micromachined Ultrasonic Transducers and Acoustic

Sensors Based on Piezoelectric Thin Films, Journal of Electroceramics, 12, 101 –

108

Newnham, R E., Skinner, D P & Cross, L E (1978) Connectivity and

piezoelectric-pyroelectric composites, Mat Res Bull, 13, 525 – 536

Or, Y., et al (2003) Modeling of poling, piezoelectric, and pyroelectric properties of

ferroelectric 0-3 composites, J Appl Phys 94 (5)

Pan, Q., et al (2007) Intense blue-light emission from hydrothermally synthesized

lead zirconate titanate platelets Materials Letters, 61, (4-5), 1210–1213

Pelaiz-Barranco, A & Marin-Franch, P (2005) Piezo- pyro, ferro-, and dielectric properties of

ceramic/polymer composites obtained from two modifications of lead titanate, J Appl Phys., 97, 03411 – 034414

Ploss, B., & Kopf, S (2006) Improving the pyroelectric coefficient of ceramic/

polymer composite by doping the polymer matrix, Ferroelectrics,

338, 145 – 151

Ploss, B., et al (2001) Poling study of PZT/P(VDF-TrFE) composites, Composites Science and

Technology, 61, 957 – 962

Pontes, D S L., et al (2001) Microstructural, dielectric and ferroelectric properties of

calcium-modified lead titanate thin films derived by chemical processes, J European Ceram Soc., 21, 1107 – 1114

Pontes, W., et al (2010) PZT, for measuring energy fluence rate of X-ray used in superficial

câncer therapy, Instr Sci Technol., 38, 210 – 219

Poon, Y M & Shin, F G (2004) A simple explicit formula for the effective dielectric constant

of binary 0-3 composites, J Mater Sci., 39, 1277 – 1281

Rao, K J., et al (1999) Synthesis of Inorganic Solids Using Microwaves, Chem Mater., 11,

882-895

Ren, T-L., et.al (2003) Piezoelectric and ferroelectric films for microelectronic applications,

Mater Sci.and Eng B99, 159 – 163

Renxin X., et al (2006) Dielectric and piezoelectric properties of 0-3 PZT/PVDF composite

doped with polyaniline, Journal of Wuhan University of Technology – Mater Sci Ed.,

21 (1), 84 – 87

Sa-Gong, et al (1986) Poling flexible piezoelectric composites, Ferroelectrics Letters, 5, 13’ –

142

Sakamoto, W K., De Souza, E & Das-Gupta, D K (2001) Electroactive properties of flexible

piezoelectric composites, Materials Research, 4 (3), 201 – 204

Sakamoto, W K., et al (2006) PTCa/PEEK composite acoustic emission sensors, IEEE Trans

Dielectr Electr Insul., 13 (5), 1177 – 1182

Sakamoto, W K., Marin-Franch, P & Das-Gupta, D K (2002) Characterization and

application of PZT/PU and graphite doped PZT/PU composite, Sensors and Actuators A, 100, 165 – 174

Schwede, J W., et al (2010) Photon-enhanced thermionic emisión for solar concentrador

Systems, Nature Materials, 9, 762 – 767

Lead Titanate-Based Nanocomposite:Fabrication,

Characterization and Application and Energy Conversion Evaluation 275 Shimomura, K., et al (1991) Preparation of lead zirconate titanate thin film by hydrothermal

method, Jpn J Appl Phys., 30, 2174 – 2177

Sodano, H A., Park, G & Inman, D J (2004) Estimation of electric charge output for

piezoelectric energy harvesting, Strain, 40, 49 – 58

Soman J.& O’Neal, C B (2011) Fabrication and Testing of a PZT Strain Sensor for Soil

Applications, IEEE Sensors Journal, 11 (1), 78 – 85

Sosnin, A (2000) Image infrared converters based on ferroelectric-semiconductor thin-layer

systems, Semiconductor Physics, Quantum Electronics & Optoelectronics, 3 (4), 489 –

495

Umeda, M., Nakamura, K & Ueha, S (1997) Energy storage characteristics of a

piezo-generator using impact induced vibration, Jpn J Appl Phys., 36, 3146 – 3151

Wang, C.M.; et al (2000) Calcium modified lead titanate thin films for pyroelectric

applications, ISAF 2000 Proceedings of the 12th IEEE International Symposium on Applications of Ferroelectrics - ISAF, vol 2, 771 – 774

Wang, D-A & Ko, H-H (2010) Piezoelectric energy harvesting from flow-induced vibration,

J Micromech Microeng 20, 025019

Wei, N., et al (2007) Effect of electrical conductivity on the polarization behaviour and

pyroelectric, piezoelectric property prediction of 0-3 ferroelectric composites, J Phys D: Appl Phys., 40, 2716 – 2722

Wong, C K & Shin, F G (2006) Effect of electrical conductivity on poling and the dielectric,

pyroelectric and piezoelectric properties of ferroelectric 0-3 composites, J Mater Sci., 41, 229 – 249

Wong, C K & Shin, F G (2005) Electrical conductivity enhanced dielectric and piezoelectric

properties of ferroelectric 0-3 composites,

J Appl Phys 97, 064111

Wong, C K., Wong, Y W & Shin, F G (2002) Effect of interfacial charge

on polarization switching of lead zirconate titanate particles in lead

zirconate titanate/polyurethane composites, J Appl Phys., 92 (7), 3974 –

3978

Yu N Zakharov, A V Borodin, & V Z Borodin (2007) Pyroelectric properties of PZT

-type ferroelectric ceramics in the morphotropic phase-transition region ,

Bulletin of the Russian Academy of Sciences: Physics , 71, (5), 709-710

Zaghete, M A., et al (1999) The Effect of Isostructural Seeding on the Microstructure and

Piezoelectric Properties of PZT Ceramics, Ceramics International, 25, 239 - 244

Zaghete, M A., et al (1992) Phases Characterization In PZT Obtained From

Organic Solutions Of Citrates Journal of the American Ceramic Society, 75, 2088 -

2093

Zhang, Q Q., et al (2006) High frequency broadband PZT thick film ultrasonic transducer

for medical imaging applications, Ultrasonics, 44 , e711 - e715

Zheng B., Chang, C-J & Gea, H C (2009) Topology optimization of energy

harvesting devices using piezoelectric materials, Struct Multidisc Optim., 38, 17

– 23

Ferroelectrics – Material Aspects

276

Zhou, Y., et al (2005) Effects of polarization and permittivity gradients

and other parameters on the anomalous vertical shift behavior of

graded ferroelectric thin films, J Appl Phys., 98, 034105

Part 3 Lead-Free Materials

14

Barium Titanate-Based Materials –

a Window of Application Opportunities

1National Institute of Advanced Industrial Science and Technology,

Fig 1 Crystalline structure of BT material above Curie temperature

Below the Curie temperature, the crystalline cell is suffering a series of changes: to tetragonal (at 1200C), from tetragonal to orthorhombic (at 00C) and from orthorhombic to rhombohedral (at –900C) in which the material has ferroelectric properties

Theories concerning the ferroelectric behavior of crystalline materials that have a perovskite structure pinpoint the important role played by the spatial oxygen arrangement having an ion in its center, to the ferroelectrical properties Taking this into consideration it is easy to predict that a change in spatial alignment of the oxygen octahedra or a substitution of the central ion (B-site substitution) can modify the ferroelectric behavior of the material Change

in spatial alignment of the oxygen octahedra can be also made by (so called) A-site substitution, when an A-site ion is substituted with another ion In the case of barium titanate, it has been found that substitutions can make the temperature of paraelectric to ferroelectric transition to shift towards lower or higher values and, in some conditions, the

Ti O Ba

Ferroelectrics – Material Aspects

in this class is (Ba1-x,Srx)TiO3 (BST), one of the most studied solid solution due to its stability and the wide range of possible applications that can use its electrical properties

A B-site substitution is also responsible of changing the degree of ordering in the solid solution resulting in a shift of Curie temperature and the appearance of the relaxor behavior when the local ordering of B-sites will make it favorable In this category there is no widely studied BT-based material because their properties were comparable to other ferroelectric materials such as lead zirconate titanate (PZT), pure barium titanate, lead titanate or even barium strontium titanate However, it has been found that small amounts of BaZrO3 or BaHfO3 included in BT can make it a candidate material for pyroelectric sensor, having electrical characteristics superior of those of lead lanthanum zirconate titanate (PLZT) or BST, materials that were commonly used for such applications

As mentioned earlier, (Ba,Sr)TiO3 (BST) solid solutions are one of the most investigated ceramic materials because the shift of ferroelectric phase transition towards lower temperatures can easily be controlled by adjusting the Ba/Sr ratio while maintaining acceptable high dielectric constants coupled with good thermal stability Ba (Ti,Sn)O3 (BTS) solid solutions are another subclass of materials that can be used for specific application For

a given application, to achieve the desired properties in the BST or BTS system, compositional control should be considered along with the preparation method and/or deposition method in the final device structure

From many applications that can incorporate BT-based materials, here only optimization for two applications will be discussed in detail: dielectric bolometer mode of infrared sensor and embedded multilayered capacitor structures Since the requirements for ferroelectric materials suitable for dielectric bolometer mode of infrared sensor and embedded multilayered capacitor structures are different, a good selection of ferroelectric material and fabrication method is necessary to ensure high quality ceramic layers for these applications

As a result, BTS thin films have been fabricated using metal-organic decomposition method

as a suitable process to ensure good quality films for dielectric bolometer mode of infrared sensing applications In the case of films for embedded multilayered capacitor applications, since the target require a low temperature fabrication technique, BST thick films have been fabricated using a relatively new deposition technique called aerosol deposition method, developed at National Institute of Advanced Industrial Science and Technology by Dr Akedo, one of the coauthors of this paper, a fabrication method that allows fabrication of thick and dense ceramic layers at room temperature

2 Preparation and characterization of BTS thin films for dielectric bolometer mode of infraredd sensor applications

One important characteristic for a material to be suitable for dielectric bolometer (DB) mode

of infrared sensor applications is to have a large Temperature Coefficient of Dielectric constant

(TCD)

Barium Titanate-Based Materials – a Window of Application Opportunities 281

( ( ) ( ( ))2

From 1990, Ba(Ti1-x,Snx)O3 solid solution captured the attention of the researchers because of

his stable ferroelectric properties in the vicinity of the Curie point that makes it a good

candidate for specific applications Because it belongs to a class of ferroelectric materials that

show a diffuse phase transition (DPT) who have promising properties behavior that can be

used for various applications such as sensors, actuators or high permittivity dielectric

devices, this solid solution captured the attention of many research groups as a suitable

active material Investigation made with bulk Ba(Ti1-x,Snx)O3 samples revealed that, if

BaSnO3 content is 30% or more, the solid solutions of Ba(Ti1-x,Snx)O3 have relaxor behavior

(Mueller et al., 2004; Lu et al., 2004; Yasuda et al., 1996; Xiaoyong et al., 2003) Moreover,

Yasuda and al observed a deviation of the dielectric constant from the Curie-Weiss law

(that is specific for relaxor ferroelectrics) even when BaSnO3 content is between 10 and 20%,

but only in a narrow temperature region above Curie point, and a relaxor behavior for

samples in witch the BaSnO3 content is above 20%

More recently, some authors see in Ba(Ti1-x,Snx)O3 a candidate to replace (Ba,Sr)TiO3 in

microwave applications (Lu et al., 2004; Jiwei et al., 2004) Jiwei et al showed that, in some

conditions, tunability of a metal-ferroelectric-metal (MFM) structure could be as high as 54%

at an applied field of 200 kV/cm and a frequency of 1 MHz

A more important indirect result has shown by Tsukada et al where, from the dielectric

constant versus temperature for a Ba(Ti1-x,Snx)O3 (BaSnO3 content of 15%) thin film with a

thickness of 400 nm deposited by PLD on Pt/Ti/SiO2/Si, a value close to 11% at 250C can be

calculated

2.1 Fabrication of BTS thin films by metal-organic decomposition process

In the processing of the thin films, the goal is not only to reduce the cost and time in

fabrication process but, more important, is to optimize the film properties for specific

applications Metal-organic decomposition process (MOD) has some advantages in

comparison with other widely used deposition techniques: precise control of stoichiometry,

high homogeneity, large area of deposition and simple equipment and process flow

However, one of the biggest problems implying this technique is that is not possible to

fabricate crystalline thin films with epitaxial or columnar structure and that the density of

the material is lower than the one obtained by other technique High quality films can still

be obtained by this process comparing with other techniques and, along with the

advantages offered by MOD convinced many researchers to use it in their investigations

Liquid solution of BTS was prepared by mixing barium isopropoxide [Ba[OCH(CH3)2]2],

titanium butoxide [Ti[O(CH2)3CH3]4] tin isopropoxide [Sn[OCH(CH3)2]4] and

1-methoxy-2-propanol supplied by Toshima MGF CO.LTD

The Ba(Ti0.85,Sn0.15)O3 (BTS) solution was deposited on Pt(240nm)/Ti(60nm)

/SiO2(600nm)/Si substrates by spin-coating at 500 rpm for 5 seconds followed by another 20

seconds at 2200 rpm This step was performed in enriched N2 atmosphere (1-5 l/min flow)

to avoid moisture, because the solution is highly hygroscopic After spin coating, the film

was moved quickly on a hot plate and dried at 2500C for one minute followed by 10 minutes

drying into an oven at the same temperature in air After drying, the BTS films were

pyrolyzed at 4500C for 10 minutes into an oven in enriched O2 atmosphere (1 l/min

Ferroelectrics – Material Aspects

282

Fig 2 Process flow of the BTS thin films prepared by MOD

Fig 3 TG-DTA analysis results of the BTS MOD-solution

flow) Spin-coating / drying / pyrolyzing sequence was repeated another 4 times before annealing in enriched O2 atmosphere (1 l/min flow) for 10 minutes was performed The BST15 thin films were annealed at 6000C, 7000C, 7500C or 8000C The deposition and heat treatment were repeated 20 times before a final annealing was performed for 20 minutes in

O2 enriched atmosphere The schematic representation of the deposition steps is shown in Figure 2 Differential thermal analysis (DTA) and thermo-gravimetric analysis (TG) (Figure 3) were used to determine the thermal decomposition behavior of the BTS solution and to select the appropriate temperatures for drying and baking DTA curve shows an endothermic peak at 1030C corresponding to solvent evaporation point and two exothermic

BTS solutionSpin coatingDryingPre-bakingAnnealing Final annealing

-100 -80 -60 -40 -20 0

0 0.5 1 1.5 2 2.5 3

-100 -80 -60 -40 -20 0

0 0.5 1 1.5 2 2.5 3

Barium Titanate-Based Materials – a Window of Application Opportunities 283 peaks at 350 and 3700C, temperatures that correspond to precursor decomposition and formation of BTS compound The TG curve showed that the total mass of the investigated liquid decreases rapidly at the beginning, the solution loosing almost 94% of its mass at

1800C and slowly loosing more, reaching -97% at 3800C The weight loss is insignificant above 3800C

According to TG-DTA results, a drying temperature over 1800C and a baking temperature over 3700C are necessary A drying temperature of 2500C and baking temperature of 4500C were selected to ensure full solvent evaporation in short time and to minimize as much as possible the stress and defects caused by a further weight reduction during annealing and a rapid complete precursor decomposition and BTS formation

The thickness of the BTS15 films obtained by this process was about 360nm

After BTS thin films preparation was completed, Pt/Ti electrodes were formed on the film

by RF sputtering to make BTS capacitors After completion of BTS capacitor fabrication, for films annealed at 7000C, a post electrode-forming annealing was performed at temperature varying from 200 to 3500C in air and at 3000C in high vacuum for 60 minutes

In order to obtain high quality films suitable for DB-mode of infrared sensing applications (high values of TCD), the BTS thin film properties have been studied for different fabrication conditions and the results were used to optimize the deposition conditions for improved BTS thin films The influence of annealing temperature and postannealing treatment on physical and electrical properties of the fabricated BTS thin films was investigated aiming an increase in TCD values near room temperature The temperature of maximum permittivity for the fabricated BTS thin films was found to be near 130C

2.2 Annealing and postannealing treatment effect on BTS thin film properties

The annealing effect on the properties of the fabricated BTS thin films has been checked first

in order to optimize the fabrication conditions

Fig 4 XRD patterns of the BTS thin films annealed at different annealing temperatures

In Figure 4, XRD patterns of the films annealed at temperature ranging from 6000C to 8000C are showed The films annealed at 6000C are still amorphous but for films annealed at 7000C and higher, crystal structure has been detected The films have strong (110) peaks suggesting that the crystalline BTS films have a preferential orientation along (110)

Ferroelectrics – Material Aspects

284

direction The other peaks, assignable to a cubic perovskite type structure, are also present but their intensities are much smaller than the intensity of (110) peak The preferred orientation and intensity ratios among the peaks revealed little distinct differences among these films as a function of annealing temperature The average grain size was estimated from the half-width of the x-ray diffraction peak using Scherrer’s formula to be in the 33.3 –

50 nm range

For films fabricated at annealing temperatures of 700, 750 and 8000C, leakage currents, C-V and temperature dependence of capacity (and through it, the permittivity dependence) were measured and analyzed Except the temperature dependence of capacity, the other electrical measurements were performed at room temperature, well above the temperature of maximum permittivity

The leakage current measurements showed that the films annealed at 7500C have a higher leakage current than films annealed at 7000C and 8000C (Figure 5) The reason for this behavior is still not clearly understood Because films with small leakage currents are desired the films annealed at 7500C cannot be considered suitable for DB-mode infrared sensing applications For this reason the attention was focused on the films annealed at

7000C and 8000C

Fig 5 Leakage current for BTS films annealed at different temperatures

The investigations of the temperature influence on the dielectric loss (Figure 6) revealed that the dielectric loss increases with increase in annealing temperature Moreover, the dielectric loss for films annealed at 8000C shows large temperature dependence compared with films annealed at 700 and 7500C On the other hand, the films annealed at 7000C have the dielectric loss very little affected by the increase in the annealing temperature

In Figure 7, temperature dependence of capacitance for films annealed at 7000C and 8000C has been plotted The variation of capacitance for BTS samples annealed at 7000C is more pronounced than for the samples annealed at 8000C

Reviewing the results obtained after physical and electrical properties in becomes clear that annealing at 7000C is more suitable in obtaining BTS thin films with good properties for DB-mode of infrared sensor applications

1E-3 0.01 0.1 1 10

Barium Titanate-Based Materials – a Window of Application Opportunities 285

Fig 6 Dielectric loss vs sample temperature for BTS films annealed at different

temperatures

Fig 7 Capacitance vs sample temperature for BTS films annealed at 7000C and 8000C The effect of postannealing temperatures on physical and electrical properties of BTS thin films was investigated keeping in mind that the films should be suitable for DB-mode of infrared sensor The annealing temperature has been set to 7000C as a result of annealing temperature effect investigations performed earlier After the top-electrode deposition, a postannealing treatment has been performed at temperatures of 200, 300 and 3500C in air and at 3000C, in vacuum for 60 minutes The results of the investigations made on BTS samples are summarized in Table 2

250 255 260 265 270 275

280 415

410

265 260 255 250