Ferroelectrics Material Aspects Part 2 pdf

BST and Other Ferroelectric Thin Films by CCVD and Their Properties and Applications 25 0.5 1 1.5 2 2.5 3 3.5 4 4.5 Frequency (GHz) -7 -6.5 -6 -5.5 -5 -4.5 -4 -3.5 -3 -2.5 -2 -1.5 -1 Insertion Loss in dB 3 GH z -4.326 dB DB(|S(2,1)|) 0V DB(|S(2,1)|) 05 V DB(|S(2,1)|) 10V DB(|S(2,1)|) 15V DB(|S(2,1)|) 20V DB(|S(2,1)|) 25V DB(|S(2,1)|) 30V DB(|S(2,1)|) 35V 0.5 1 1.5 2 2.5 3 3.5 4 4.5 Frequency (GHz) -40 -35 -30 -25 -20 -15 -10 -5 0 Return Loss in dB 3 GHz -11.53 dB DB(|S(1,1)|) 0V DB(|S(1,1)|) 05V DB(|S(1,1)|) 10V DB(|S(1,1)|) 15V DB(|S(1,1)|) 20 V DB(|S(1,1)|) 25 V DB(|S(1,1)|) 30V DB(|S(1,1)|) 35V Fig. 30. (a) Insertion loss, S21 and (b) return loss, S11 of 3 GHz phase shifter 11.522.533.544.55 Frequency (GHz) 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 400 Insertion Phase Shift in Degrees 3 GHz 376.3 Deg 05V ( Deg ) 10 V (Deg) 15 V (Deg) 20 V (Deg ) 25 V (Deg ) 30V ( Deg ) 35V ( Deg ) Fig. 31. Phase shift of the 3 GHz phase shifter at different frequencies and bias voltages (a) (b) Ferroelectrics – Material Aspects 26 5. Conclusions As a summary, high quality epitaxial or textured ferroelectric and dielectric thin films, including BST (both single layer and nanostructured multilayer), PZT, and CCT, have been successfully deposited by the proprietary CCVD process onto various substrates, including sapphire and single crystal STO, MgO, and LAO etc. Excellent electrical properties have been achieved on these ferroelectric and dielectric thin films. High performance microwave devices that can be used up to Ka band, such as tunable MEMS filters and CDMA filters, have been designed and fabricated on BST based ferroelectric thin films. The performance of these microwave devices are summarized as following:  MEMS Ka-band tunable bandpass filters (both center frequency and bandwidth are tunable): the best insertion loss of 3 dB when biased, and the bandwidths of 3 and 7.8% for 3-pole narrowband and wideband, respectively;  CDMA Tx tunable filters: insertion loss <2 dB, VSWR <1.5:1, center frequency shifting from 1.85 to 1.91 GHz, Rx zero (@1.93 GHz) rejection >40 dB, DC bias <10 V;  X- to Ku-band tunable bandpass filters: insertion loss of ~5 dB @11.5 GHz (0V) to 3 dB @14 GHz (30 V), VSWR <2:1, DC bias <30 V, 6 × 1.5 × 0.5 mm in footprint;  X-band back-to-back 4-pole bandpass filters: Insertion loss from 5.4 dB at 9.1 GHz to 1.84 dB at 10.25 GHz with an analog tuning of 12.6%; return loss <10 dB over the whole X-band frequency range;  Ka-band ring filters: insertion loss of 2.3 and 2.0 dB for 0 and 30 V, respectively; 3-dB bandwidth of 20% for both bias states; tuning from 31.6 to 33.7 GHz, a 6.3% tunability;  3 GHz phase shifter: The insertion loss at is 4.3 dB at 15 V and 3 GHz. The figure of merit is 89.4°/dB at 0V. A phase shift of 361° is measured at 30V. 6. References Adams, T. B., Sinclair, D. C., and West, A. R. (2002). Giant Barrier Layer Capacitance Effects in CaCu 3 Ti 4 O 12 Ceramics. Advanced Materials, Vol.14, No.18, (Sept 2002), pp. 1321- 1323, ISSN 1521-4095 Bao, P., Jackson, T. J., Wang, X., and Lancaster, M, J. (2008). Barium Strontium Titanate Thin Film Varactors for Room-Temperature Microwave Device Applications. J. Phys. D: Appl. Phys., Vol.41, No.6, (June 2008), pp. 063001, ISSN 0022-3727 Baringay, C. K. & Dey, S. K. (1992). Observation of sol‐gel solid phase epitaxial growth of ferroelectric Pb(Nb,Zr,Ti)O 3 thin films on sapphire. Appl. Phys. Lett.,Vol. 61, No. 11, (September1992), pp.1278-1280, ISSN 0003-6951 Bochu, B., Deschizeaux, M. N., and Joubert, J. C., (1979). Synthése et Caratérisation d’une Série de Titanate Pérowskite Isotypes de [CaCu 3 ](Mn 4 )O 12 . J. 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Lead – based ferroelectric ceramics represented by Pb (Zr,Ti)O 3 (PZT), have been widely used for piezoelectric transducers, sensors and actuators due to their excellent piezoelectric properties. However, the evaporation of harmful lead oxide during preparation causes a crucial environment problem. Therefore, it is necessary to develop environment – friendly lead – free piezoelectric ceramics to replace the PZT – based ceramics, which has become one of the main trends in present development of piezoelectric materials. Sodium bismuth titanate, Na 0.5 Bi 0.5 TiO 3 (abbreviate as NBT), discovered in 1960 (Smolenskii et al., 1960), is considered to be a promising candidate of lead – free piezoelectric ceramics (Pookmaneea et al., 2001; Isupov, 2005; Panda, 2009; Zhou et al., 2010). NBT is a relaxor ferroelectric material with the general formula A ’ x A” 1-x BO 3 . The ferroelectricity in NBT ceramic is attributed to (Bi 1/2 Na 1/2 ) 2+ ions, especially Bi 3+ ions at the ,,A” site of the perovskite structure (ABO 3 ) and due to rhombohedral symmetry at room temperature. It has high Curie temperature (T c = 320°C), and shows diffuse phase transition (Suchanicz et al., 2000; Suchanicz et al., 2001; Raghavender et al., 2006). However, the piezoelectric properties of NBT ceramics are not good enough for most practical uses. In order to enhance the properties and meet the requirements for practical uses, it is necessary to develop new NBT – based ceramics (Raghavender et al., 2006; Zhou et al., 2010). Researches have investigated many dopants into NBT ceramics (Panda, 2009). Also, it is desirable to fabricate ceramics with a textured microstructure in order to improve the properties (Hao et al., 2007). The ferroelectric ceramic powders are synthesized trough conventional solid – state method which needs high calcination temperature and repeated grindings (Lu et al., 2010). In order to eliminate these defects, the wet chemical synthesis techniques have been developed, for instance hydrothermal method (Cho et al., 2006; Wang et al., 2009), sol – gel method (Xu et al., 2006; Mercadelli et al., 2008), and molten salt method (Zeng et al., 2007; Li et al., 2009). But the hydrothermal and sol – gel synthesis are usually long and complex processes, use hazardous solvents such as 2-methoxyethanol, and result in agglomerated particles (Bortolani & Dorey, 2010). Moreover, in the sol –gel method the cost of starting materials is high (Li et al., 2009). Ferroelectrics – Material Aspects 32 Molten salt synthesis (MSS) is a process that yields large amounts of ceramic powders in a relatively short period of time. Moreover, it is a suitable method for preparation of complex oxide compounds with anisotropic particle morphologies. In this technique starting materials are mixed together with a salt (usually alkaline chloride and sulphate) and then heat treated at a temperature higher than the melting point of the salt. The melting temperature of the salt system can be reduced by using a eutectic mixture of salts, e.g. the use of NaCl – KCl instead of pure NaCl reduces the melting point from 801 to 657°C. A reaction between the precursors takes place in the molten salt (the flux) and the solid product obtained is separated by washing of the final mixture with hot deionised water. The typical starting materials are oxides, but carbonates, oxalates and nitrates can also be used. There are several requirements for the selection of salt to be used for MSS. First, the melting point of the salt should be relatively low and appropriate for synthesizing of the required phase. Second, the salt should possess sufficient aqueous solubility in order to eliminate it easily after synthesis by washing. Finally, the salt should not react with the starting materials or the product (Bortolani & Dorey, 2010; Hao et al., 2007). MSS has been used to form various ceramic powders such as niobates relaxors (Yoon et al., 1998), Bi 4 Ti 3 O 12 (Kan et al., 2003), ZnTiO 3 (Xing et al., 2006), BaTiO 3 (Zhabrev et al., 2008) and Pb(Zr, Ti)O 3 (Cai et al., 2008; Bortolani & Dorey, 2010). It was found that ternary compound Na 0.5 Bi 0.5 TiO 3 was formed in the solid – state process through the intermediate binary compound, i.e. bismuth titanate – Bi 4 Ti 3 O 12 (Zaremba, 2008). Bi 4 Ti 3 O 12 (abbreviate as BIT) belongs to the Aurivillius family with a general formula (Bi 2 O 2 )[A m-1 (B) m O 3m+1 ], which consists of (Bi 2 O 2 ) 2+ sheets alternating with (Bi 2 Ti 3 O 10 ) 2 - perovskite – like – layers (Aurivillius, 1949, as cited in Stojanović et al., 2008). In general formula m represents the number of octahedra stacked along the direction perpendicular to the sheets, and A and B are the 12- and 6- fold coordination sites of perovskite slab, respectively. This kind of structure promotes plate – like morphology (Dorrian et al., 1971, as cited in Stojanović et al., 2008). In this paper, Na 0.5 Bi 0.5 TiO 3 powders were prepared by molten salt synthesis in the presence pure NaCl or NaCl - KCl as fluxes. The first stage of the study related to direct synthesis of NBT via MSS from Na 2 CO 3 , Bi 2 O 3 and TiO 2 . For comparison, the synthesis of NBT by the conventional method (CMO – conventional mixed oxides) was investigated. The second stage included obtaining intermediate binary compound BIT via MSS from oxide precursors, i.e. Bi 2 O 3 and TiO 2 , and then synthesis of NBT via MSS using BIT, Na 2 CO 3 and TiO 2 as starting materials. The details pertaining to studies of synthesis of NBT and an Aurivillius – structured BIT precursor are reported in the following sections. 2. Synthesis of ferroelectric Na 0.5 Bi 0.5 TiO 3 Chemically pure powders of Bi 2 O 3 , TiO 2 (rutile) and Na 2 CO 3 were used as starting materials. The Na 0.5 Bi 0.5 TiO 3 (NBT) was prepared by the following two routes: Na 2 CO 3 + Bi 2 O 3 + 4TiO 2 → 4Na 0.5 Bi 0.5 TiO 3 + CO 2 (1) Bi 4 Ti 3 O 12 + 5TiO 2 + 2Na 2 CO 3 → 8Na 0.5 Bi 0.5 TiO 3 + 2CO 2 (2) In route (1), the starting materials were weighed in the proportion to yield NBT and mixed in isopropyl alcohol employing an agate mortar and pestle for 1 h. Using MSS method, the dry mixture of the precursors in the stoichiometric composition was mixed with an aqual Synthesis of Ferroelectric Na 0.5 Bi 0.5 TiO 3 by MSS (Molten Salt Synthesis) Method 33 weight of salt. Salts used in this experiment were NaCl and eutectic mixture of 0.5NaCl – 0.5KCl, i.e. 43.94% NaCl – 56.06% KCl (by weight). The mixture of the precursors and flux was dried at 120°C for 2 h for complete removal of isopropyl alcohol, placed in a Pt crucible and heated in a sealed alumina crucible (to prevent salt evaporation) at temperatures between 800°C and 1100°C for a different time period. After thermal treatment the chlorides were removed from the products by washing with hot deionized water several times until the filtrates gave no reaction with silver nitrate solution. The powders were finally dried at 100°C for 2 h. NBT powders were also prepared by a conventional mixed oxide method (CMO) for comparison. All the syntheses were carried out in a conventional electric furnace. Platelike Bi 4 Ti 3 O 12 (BIT) particles were obtained by MSS method in 0.5NaCl – 0.5KCl flux (abbreviate as NaCl – KCl) in the same way as described above. Temperature of thermal treatment ranging from 700°C to 1100°C for a different time period. In route (2), BIT crystals produced earlier were subjected to second molten salt synthesis. Na 2 CO 3 and TiO 2 were added to give the total composition of NBT. Again, pure NaCl or NaCl – KCl mixture was added (weight ratio of precursors to flux = 1:1). Finally, the phase composition of the synthesized samples was analyzed by the powder X- ray diffraction (XRD; model 3003 TT, Seifert) using Ni – filtered Cu K α radiation. The microstructure was observed by a scanning electron microscope (SEM; model BS 340, Tesla). The samples were coated by a gold layer by using a metal – coating plant under a vacuum. X–ray energy dispersive spectra (EDS) were measured using a Hitachi S-3400 N scanning electron microscope with an EDS system Thermo Noran. 2.1 Synthesis of Na 0.5 Bi 0.5 TiO 3 from Bi 2 O 3 , TiO 2 and Na 2 CO 3 Fig. 1 represents the XRD patterns of the selected powders synthesized through route (1), i.e. directly from Bi 2 O 3 , TiO 2 and Na 2 CO 3 via MSS (NaCl flux) and CMO. Similar trends were also observed for NBT produced using NaCl- KCl flux. The particle morphology of the starting materials and synthesized powders is compared in Figs 2 – 4. NBT perovskite phase was observed in all the prepared samples. A comparison of interplanar spacings determined from XRD patterns of the samples prepared by a conventional solid state reaction and via MSS shows that agreement is quite satisfactory. Analysis of XRD patterns of NBT samples obtained via MSS has not shown displacement of maxima of diffraction peaks as the NaCl-KCl flux was used. Isometric particles are found to exist in the samples of NBT. Typical micrograph of the NBT powder prepared by CMO is shown in Fig. 3a. There is high degree of agglomeration in this powder. The NBT particles prepared directly by CMO and MSS (NaCl flux) are very small (about 1 μm). The size of the particles increased with increasing temperature, especially, as NaCl-KCl flux was used. Probably, this is mainly due to the different melting points for each salt used. NaCl and 0.5 NaCl – 0.5 KCl have melting points of about 800°C and 650°C, respectively. According to (Cai et al., 2007, as cited in Bortolani & Dorey, 2010) the solubility of the starting materials in the molten salt plays an important role in the synthesis as it has an influence on the final product morphology. For a simple two reactant system, two different cases can be distinguished: either both reactants are equally soluble in the molten salt or one oxide is more soluble than the other (Li et al., 2007, as cited in Bortolani & Dorey, 2010). In the first case (dissolution – precipitation mechanism) both reactants fully dissolve, react in the molten salt and the final product precipitates from the molten salt after formation. The shape of the product has no connection with the shape of the starting materials. In the second case, the more soluble precursor dissolves in the salt and diffuses to the less soluble [...]... powders Journal of Sol-Gel Science and Technology, Vol.46, (July 20 07), pp.39-45, ISSN 0 928 -0707 48 Ferroelectrics – Material Aspects Panda, P.K (20 09) Review: environmental friendly lead-free piezoelectric materials Journals of Materials Science, Vol.44, (April 20 09), pp 5049-50 62, ISSN 0 022 -24 61 Pookmaneea, P.; Phanichphanta, S & Heimann, R.B (20 01) Synthesis and Properties of Bismuth Sodium Titanate (BNT)... 1081-1084, ISSN 0 021 -4 922 Isupov, V.A (20 05) Ferroelectric Na0.5Bi0.5TiO3 and K0.5Bi0.5TiO3 Perovskites and Their Solid Solutions Ferroelectrics, Vol.315, (December 20 03), pp 123 -147, ISSN 0015-0193 Kan, Y.; Jin, X.; Wang, P.; Li, Y.; Cheng, Y-B & Yan, D (20 03) Anisotropic grain growth of Bi4Ti3O 12 in molten salt fluxes Materials Research Bulletin, Vol.38, (June 20 02) , pp.567-576, ISSN 0 025 -5408 Kimura,... (Bi2Ti2O10 )2- (pseudo-) perovskite layers interleaved by (Bi2O2 )2+ fluorite layers After the reaction with the complementary reactants (Na2CO3 and TiO2), the layer-structured BIT particles were transformed to the perovskite NBT Although there are works reporting the transformation as a process from a lamellar phase to a perovskite phase (Schaak & Mallouk, 20 00), the process involving the (Bi2O2 )2+ ... Society, Vol. 122 , No. 12, (September 1999), pp 27 98 -28 03, ISSN 00 02- 7863 Smolenskii, G.A.; Isupov, V.A.; Agranovskaya, A.I & Krainik, N.N (1960) New ferroelectrics with complex compounds IV Fizika Tverdogo Tela, Vol .2, No.11, (June 1960), pp 29 82- 2985, ISSN 1063-7834 (in Russian) Stojanović, B.D.; Paiva-Santos, C.O.; Cilense, M.; Jovalekić, Č & Lazarević, Z.Ž (20 08) Structure study of Bi4Ti3O 12 produced... No.3, (July 20 05), pp 1150-11 52, ISSN 00 02- 7 820 Xu, Q.; Chen, S.; Chen, W.; Huang,;D.; Zhou, J.; Sun, H & Li, Y (20 06) Synthesis of (Na0.5Bi0.5) TiO3 and (Na0.5Bi0.5)0.92Ba0.08TiO3 powders by a citrate method Journal of Materials Science, Vol.41, (December 20 03), pp 6146-6149, ISSN 0 022 -24 61 Yoon, K.H.; Cho, Y.S & Kang, D.H (1998) Review Molten salt synthesis of lead-based relaxors Journal of Materials... Vol.33, (October 1997), pp 29 77 -29 84, ISSN 0 022 -24 61 Zaremba, T (20 08) Thermoanalytical study of the synthesis of Na0.5Bi0.5TiO3 ferroelectric Journal of Thermal Analysis and Calorimetry, Vol. 92, No .2, (June 20 07), pp 583-587, ISSN 1388-6150 Zeng, J.T.; Kwok, K.W & Chan, H.L.W (20 07) KxNa1-xNbO3 Powder Synthesized by Molten-Salt Process Materials Letters, Vol.61, (Febuary 20 06), pp 409-411, ISSN 0167-577X... S-X (20 07) Lead-Free SrBi4Ti4O15 and Bi4Ti3O 12 Material Fabrication Using the Microwave-Assisted Molten Salt Synthesis Method Journal of the American Ceramic Society, Vol.90, No.5, (October 20 06), pp 1659-16 62, ISSN 00 02- 7 820 Hiruma, Y.; Nagata, H & Takenaka, T (20 07) Grain Size Effect on Electrical properties of (Bi1/2K1 /2) TiO3 Ceramics Japanese Journal of Applied Physics, Vol.46, No.3A, (June 20 06),... (d) 120 min Synthesis of Ferroelectric Na0.5Bi0.5TiO3 by MSS (Molten Salt Synthesis) Method (a) (b) (c) (d) Fig 8 SEM micrographs of Bi4Ti3O 12 powders obtained via MSS at different temperatures for 4 h: (a) 700°C; (b) 800°C; (c) 900°C; (d) 1000°C 41 42 Ferroelectrics – Material Aspects 2. 2 Synthesis of Bi4Ti3O 12 The XRD patterns of selected samples BIT prepared from the mixture of Bi2O3 and TiO2 via... and Compounds, Vol.471, (August 20 07), pp 428 -431, ISSN 0 925 -8388 Lu, T.; Dai, J.; Tian, J.; Song, W.; Liu, X.; Lai, L.; Chu, H.; Huang, X & Liu, X (20 10) Synthesis of Na0.5Bi0.5TiO3 powders through hydrothermal method Journal of Alloys and Compounds, Vol.490, (July 20 09), pp 23 2 -23 5, ISSN 0 925 -8388 Mercadelli, E.; Galassi, C.; Costa, A.L.; Albonetti, S & Sanson, A (20 08) Sol-gel combustion synthesis... Ceramic Physica Status Solidi (b), Vol .22 5, (December 20 00), pp 459-466, ISSN 0370-19 72 Wang, Y.; Xu, G.; Yang, L.; Ren, Z.; Wei, X.; Weng, W.; Du, P.; Shen, G & Han, G (20 09) Hydrothermal synthesis and characterization of Na0.5Bi0.5TiO3 microcubes Ceramics International, Vol 35, (May 20 08), pp 1657-1659, ISSN 027 2-88 42 Xing, X.; Zhang, C.; Qiao, L.; Liu, G & Meng, J (20 06) Facile Preparation of ZnTiO3 . routes: Na 2 CO 3 + Bi 2 O 3 + 4TiO 2 → 4Na 0.5 Bi 0.5 TiO 3 + CO 2 (1) Bi 4 Ti 3 O 12 + 5TiO 2 + 2Na 2 CO 3 → 8Na 0.5 Bi 0.5 TiO 3 + 2CO 2 (2) In route (1), the starting materials. V DB(|S (2, 1)|) 10V DB(|S (2, 1)|) 15V DB(|S (2, 1)|) 20 V DB(|S (2, 1)|) 25 V DB(|S (2, 1)|) 30V DB(|S (2, 1)|) 35V 0.5 1 1.5 2 2.5 3 3.5 4 4.5 Frequency (GHz) -40 -35 -30 -25 -20 -15 -10 -5 0 Return Loss. (GHz) 0 20 40 60 80 100 120 140 160 180 20 0 22 0 24 0 26 0 28 0 300 320 340 360 380 400 Insertion Phase Shift in Degrees 3 GHz 376.3 Deg 05V ( Deg ) 10 V (Deg) 15 V (Deg) 20 V (Deg ) 25 V (Deg ) 30V ( Deg