Dobijanje nanokristalnih barijum titanatnih filmova definisane strukture i svojstava za primenu u mikrotalasnim tunabilnim uređajima / Preparation of nanocrystalline barium titanate based films with defined structure and propreties for application in microwave tunable devices

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<p>U poslednjih nekoliko decenija, feroelektrici su prepoznati kao dobri kandidati<br />za &scaron;irok spektar primene. Barijum titanat je jedan od najče&scaron;će istraživanih<br />perovskitnih materijala usled tipičnog feroelektričnog pona&scaron;anja na sobnoj<br />temperaturi, sa histerezisnom zavisnosti između polarizacije i električnog polja.<br />Specifična svojstva BaTiO₃ čine ovaj materijal veoma korisnim u proizvodnji<br />kondenzatora, memorija, senzora i dr. Pored toga, paraelektrična faza BaTiO₃<br />ima primenu u proizvodnji mikrotalasnih tunabilnih uređaja. BaTiO₃ pokazuje<br />paralaketrično pona&scaron;anje iznad Kirijeve temperature (120&deg;C) i veliki je izazov<br />modifikovati materijal da bude paraelektričan na sobnoj temperaturi. Delimičnom<br />supstitucijom Ba²⁺ ili Ti⁴⁺ jona, jonima Sr²⁺ ili Zr⁴⁺, respektivno, snižava<br />se Kirijeva temperatura i dolazi do pomeranja fazne transformacije feroelektri<br />čno/paraelektrično na niže temperature. Monolitna keramika na bazi bazi<br />BaTiO₃ je često istraživana kako bi se ispitale promene u strukturi i svojstvima<br />uzrokovane dodatkom dopanata, međutim ne postoji praktična primena ovih<br />materijala u mikrotalasnim tunabilnim tehnologijama. S druge strane, u trendu<br />sveop&scaron;te minijaturizacije elektronskih komponenti, tanki filmovi su prepoznati<br />kao dobri kandidati za proizvodnju tunabilnih uređaja. Jedan od ciljeva ovog<br />istraživanja bio je ispitivanje strukturnih i funkcinalnih svojstava tankih filmova na<br />bazi barijum titanata, BaTiO₃, Ba_1-xSr_xTiO₃ (x=0,1, 0,2, 0,3 i 0,4) i BaTi_1-xZr_xO₃<br />(x=0,1 i 0,2), pripremljenih hemijskom depozicijom iz tečne faze. Metalne<br />soli BaCO₃, C₄H₆O₄Sr i ZrOCl₂ H₂O i Ti(OCH₂CH₂CH₂CH₃)₄ rastvorene su<br />odvojeno u kiseloj sredini i pome&scaron;ane u transparentne solove. Inkdžet &scaron;tampa<br />i spin tehnika kor&scaron;ćene su za depoziciju funkcionalnih filmova na bazi BaTiO₃.<br />Nakon deponovanja, pripremljeni filmovi su termički tretirani na različitim<br />temperaturama do 1000&deg;C. U zavisnosti od koncentracije pripremljeni su filmovi<br />debljine od 100 do 700 nm,sa veličinom zrna od nekoliko desetina nanometara. Strukturna karakterizacija potvrdila je promene u strukturi BaTiO₃ tankih filmova<br />sa dodatkom Sr²⁺ i Zr⁴⁺. Tetragonalna (feroelektrična) faza BaTiO₃ je potvrđena<br />rentgenostrukturnom analizom i Ramanovom spektroskopijom. S druge strane,<br />smanjenje tetragonalnosti je primećeno kod dopiranih uzoraka. Promene u<br />funkcionalnosti dopiranih BaTiO₃ filmova analizirane su na osnovu dielektričnih<br />i feroelektričnih merenja. Izvr&scaron;ene analize su potvrdile feroelektrično pona&scaron;anje<br />kod BaTiO₃, dok se feroelektrični odgovor u tankim filmovima smanjuje sa<br />dopiranjem. Priprema elektroda specifičnih geometrija pogodnih za tunabilna<br />merenja različitim tehnikama depozicije bio je drugi cilj istraživanja. Tehnika spaterovanja u kombinaciji sa laserskim uklanjanjem, inkdžet &scaron;tampa i fotolitografija<br />su kori&scaron;ćene za pripremu kružnih i koplanarnih elektroda na povr&scaron;ini barijum<br />titanatnih tankih filmova. Uticaj procesnih parametara svake od pomenutih<br />metoda na dimenzionalnu preciznost pripremljenih elektroda je bio predmet istraživanja<br />u okviru teze. Odabrani laser se pokazao kao neprikladan za pripremu<br />elektroda na pripremljenim barijum titanatnim tankim filmovima. Inkdžet &scaron;tampa<br />se pokazala kao korisna u pripremi elektroda mikrometarskih fimenzija, dok je za<br />pripremu sofisticiranijih geometrija fotolitografija pokazala najbolje performanse.</p> / <p>In past few decades, ferroelectrics are recognized as good candidates for wide<br />range of applications. Barium titanate is one of the most investigated perovskite<br />materials due to typical ferroelectric behavior at room temperature, with hysteresis<br />dependence of the polarization and electric field. Specified properties<br />of BaTiO₃ make this material useful in production of capacitors, memories,<br />sensors, etc. Nevertheless, paraelectric phase of BaTiO₃ may have application<br />in production of microwave tunable devices. Barium titanate shows paraelectric<br />behavior at temperatures above the Currie temperature (120 &deg;C) and it is great<br />challenge to make material paraelectric at room temperature. Partial substitution<br />of Ba²⁺ or Ti⁴⁺ ions, by Sr²⁺ or Zr⁴⁺, respectively, decreases the Currie temperature<br />of barium titanate and moves phase transition ferroelectric/paraelectric<br />to lower temperatures. Bulk BaTiO₃was often investigated in order to improve<br />structure and functionality by addition of dopant, but do not have practical<br />application in microwave tunable technologies. On the other hand, with the<br />trend of overall miniaturization of electronic devices, thin films are recognized<br />as good candidates for production of tunable devices. One of the aims in this<br />research was investigation of structural and functional properties of barium<br />titanate based thin films, BaTiO₃, Ba_1-xSrxTiO₃ (x=0,1, 0,2, 0,3 i 0,4) and<br />BaTi_1-xZrxO₃ (x=0,1 i 0,2), prepared by chemical solution deposition. Metal<br />salts of BaCO₃, C₄H₆O₄Sr and ZrOCl₂ H₂O and Ti(OCH₂CH₂CH₂CH₃)₄were<br />separetly disolved in acetic environment and mixed in clear transparent sols.<br />Inkjet printing and spin coating were used for deposition of functional BaTiO3<br />based fims. After deposition prepared films were thermally treated at different<br />temperatures up to 1000 &deg;C. In dependence of sol concentration thickness of<br />obtained films is from 100 to 700 nm and grain size is few tens of nanometers. Structural characterization confirmed changes in structure of barium titanate thin<br />films by addition of Sr^₂₊ i Zr⁴⁺. Tetragonal (ferroelectric) phase of BaTiO₃ is<br />confirmed by X-ray diffraction and Raman spectroscopy. On the other hand, decreasing<br />of tetragonality was noticed in doped samples. Changes in functionality<br />of doped BaTiO₃ thin films were analyzed by dielectric and ferroelectric measurements.<br />Performed analysis confirmed ferroelectric behavior of barium titanate<br />thin films, and decrease in ferroelectric answer of doped films. Investigation of<br />possibility of complex shaped electrodes preparation,suitable for tunability measurements, by different deposition techniques was the second goal of this research.<br />Sputtering technique in combination with laser removal, inkjet printing and photolithography were used for preparation of complex circular and coplanar electrodes<br />on the surface of barium titanate based thin films. Influence of processing<br />parameters for the each of mentioned technique on dimensional precision of prepared<br />electrodes was investigated. Selected laser was not appropriate for production<br />of electrodes on prepared barium titanate based thin films. Inkjet printing<br />was useful for production of electrodes in micrometer range, but for more sophisticated<br />geometries photolithography shows the best performance.</p>

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Identifer	oai:union.ndltd.org:uns.ac.rs/oai:CRISUNS:(BISIS)110058
Date	15 March 2019
Creators	Vukmirović Jelena
Contributors	Srdić Vladimir, Stojanović Goran, Milanović Marija, Bobic Jelena, Stijepović Ivan
Publisher	Univerzitet u Novom Sadu, Tehnološki fakultet Novi Sad, University of Novi Sad, Faculty of Technology at Novi Sad
Source Sets	University of Novi Sad
Language	Serbian
Detected Language	English
Type	PhD thesis