PZT FILMS PREPARED BY TVA AND PLD FROM PbO 2 :TiO 2 : ZrO 2 (1:1:1) NANOCERAMIC TARGETS

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1 Digest Journl of Nnomterils nd Biostructures Vol. 6, No 1, Jnury-Mrch 2011, p PZT FILMS PREPARED BY TVA AND PLD FROM PO 2 :TiO 2 : ZrO 2 (1:1:1) NANOCERAMIC TARGETS D. SAVASTRU, D. TENCIU, C. P. LUNGU, C. VIESPE, C. GRIGORIU, R. IORDANESCU, I. D. FERARU, V. IONESCU, O. MONNEREAU c, L. TORTET c, R. NOTONIER d, C. E. A. GRIGORESCU * Ntionl Institute R&D Optoelectronics INOE 2000, 409 Atomistilor Str., P.O. Box MG-5, Mgurele, Jud. Ilfov, Romni, Ntionl Institute for Lser, Plsm nd Rdition Physics, Mgurele, Romni Ovidius University, Constnt, Romni. c Lortoire de Chimie Provence, Centre de Sint Jerome, Mrseille, Frnce d SCM-Universite de Provence, Mrseille, Frnce Led zirconte titnte (PZT) thin films on Si single crystl were prepred y two techniques: ) thermionic vcuum rc (TVA) nd ) pulsed lser deposition (PLD), using cermic trgets mde of PO 2, ZrO 2 nd TiO 2 nnopowders. Structurl chrcteristion of the smples y XRD, EDS nd micro-rmn spectroscopy revels comintions of PZT nd its constituent oxides resulting from either experiment. Morphology studies crried out y SEM nd AFM remrk smoother surfce for the PLD films thn for the TVA ones. A comprison etween the lted nd the rw zones of the PLD trget leds to the conclusion tht the lser-cermic interction eses the PZT synthesis. (Received Decemer 18, 2010; ccepted Jnury 17, 2011) Keywords: PZT, thermmionic vcuum rc deposition, Pulsed lser deposition, Rmn spectroscopy, Thin films, Structurl chrcteristion 1. Introduction Led zirconte titnte (PZT) hs ttrcted much ttention due to its excellent ferroelectric, piezoelectric, dielectric nd pyroelectric properties [1, 2]. In the form of thin/thick films PZT finds wide rnge of pplictions in non-voltile rndom ccess memories [3], piezoelectric micro-sensors [4, 5] nd intergrded cpcitors [6, 7]. A wide rnge of methods is eing used to fricte PZT films, such s chemicl vpour deposition (CVD) [8], pulsed lser deposition (PLD) [9-11], sputtering [12], metl orgnic decomposition (MOD) [13] nd sol gel [14]. The PZT films studied in this work were prepred from composite trgets y two lterntive wys: ) the thermionic vcuum rc deposition (TVA) [15] nd ) the PLD technique, with the im to understnd the mechnisms involved in the deposition processes of PZT nd thus to provide comprison nd eventully selection criterion for the most pproprite technique etween TVA nd PLD. Structurl chrcteristion through XRD, EDS nd micro-rmn spectroscopy mesurements hs een done on the films nd their originting trgets. Morphology studies resulted from SEM nd AFM investigtions. * Corresponding uthor: krisis812@yhoo.co.uk

2 Experimentl detils 2.1 Trgets preprtion Identicl trgets were used with oth TVA nd PLD deposition techniques. The trgets were prepred from high purity (99.9%) oxide powders PO 2, TiO 2 nd ZrO 2 in stoichiometric mounts 1:1:1. The powders were mixed in methnol nd milled t high energy for 4h. The resulted lend ws stirred dry nd then nneled to 900 o C for 4h in ir. A new milling step followed for 6h nd the resulted nnopowders were pressed in pellets t 60MP nd nneled to 1250 O C for 6h in seled mpoules. A finl polish ws given to the surfces of the pellets. 2.2 Film deposition TVA technique The TVA set-up is shown in the Fig.1. A detiled description of the technique is given elsewhere [15]. The cthode, node nd sustrte re set in stinless steel rection chmer. The Si sustrte-tva gun distnce ws 300mm nd the sustrte temperture ws 450 o C in ll experiments. To chieve stle dischrge during the PZT deposition processes the following prmeter vlues were used: I rc = 1.3A nd U rc = 400V. The process evolved in vcuum ( Torr t the strt of the experiment). A qurtz oscilltor hs een used to control the thickness of the film during deposition. The 100nm films thus otined were removed from the chmer 120min fter the deposition, when their temperture reched t room temperture. Fig. 1. The experimentl set-up contining the tungsten filment, PZT node, nd sustrtes S PLD technique Widely used with vrious mterils, PLD is descried in detil in mny ppers [9-11]. We employed common PLD set-up to run the PZT deposition. The films were deposited on Si sustrtes held t 450 C, using the third hrmonics of Nd:YAG lser (EKSPLA model NL301) λ=355 nm, τ= 5 nsec/pulse t repetition rte of 10 Hz. The numer of pulses on ech smple ws , t fluence of 2 J/cm 2. The preliminry pressure in the chmer ws Torr nd the oxygen pressure during the deposition ws 130 mtorr. The thickness of the films ws 100 nm s clculted from the ltion threshold nd the numer of pulses delivered on ech run. 2.3 Chrcteristion Trgets efore TVA evportion/ lser ltion s well s following the deposition processes were investigted for morphology nd structurl properties y SEM, EDS nd Rmn

3 spectroscopy. The SEM-EDS investigtions were performed with PHILIPS ESEM 30 microscope. The films were chrcterised y XRD, AFM nd Rmn spectroscopy. XRD mesurements were performed t grzing incidence on ll films using the CuK α rdition (λ =1,5421A o ) of Szimdzu 6000 X-ry diffrctometer. The unpolrised Rmn spectr were tken t room temperture with LABRAM HR 800 micro-rmn spectrometer (Hori Scientific) in the ckscttering geometry using 632nm lser source (1μm dimeter of the spot) in the rnge 130cm -1 to 900cm -1. The resolution of the spectr ws 0.5cm Results nd discussion In Fig.2 the morphology of the trgets fresh surfce (), lser lted surfce () nd TVA evported (c) cn e oserved long with the respective EDS nlysis. The concentrtions (t. %) were normlized to oxygen. t%: O 56;Zr 12;Ti 11;P 21. t% O 53;Zr 18; Ti 17;P 12. c t% O 62; Zr 17; Ti 15; P 6. Fig. 2. SEM imges of () fresh PZT trget, () lser lted region of the trget nd (c) TVA evported trget. The corresponding EDS nlyses over 100μm X 100μm surfces on ech trget re displyed, with the concentrtions of the elements normlized to oxygen. The reduced concentrtion of P in the evported/lted trgets in comprison with the rw mteril is norml, knowing tht the oiling point of led is quite low. The remining mount of P hs contriuted to the PZT synthesis, s it will e shown elow. In Fig. 3 the AFM imges of two films deposited y TVA () nd PLD () re shown. The higher roughness of the TVA film is esily oserved. Still, we suggest droplets risen on the surfce of the PLD film minly cuse the roughness. The grin size of the mteril is lso in close reltion with smoothness of the films surfces. The XRD ptterns (not shown here) correspond to

4 210 mixture of PZT perovskite phse with cler (110) pek nd crystllites of the trgets component oxides. The verge crystllite size ws clculted from the (110) pek through the Deye-Sherrer formul [16, 17] for films deposited y either techniques nd resulted in 20 nm for the PLD smples nd 40nm for the TVA ones. Fig. 3. AFM imges of PZT films deposited on Si y () PLD nd () TVA. It is to remrk the smoother surfce of the PLD film. The difference etween the grin sizes in the films deposited y the two techniques is lso ovious from the shpes of the Rmn lines. The Rmn spectr of the fresh trget, TVA nd PLD films respectively re shown in fig. 4 nd in fig. 4, the Rmn spectr of the fresh trget nd its lted region re compred. The Rmn lines in fig.4 were identified fter curves deconvolution nd fit with Lorentz-Guss functions. Fig. 4 ) Rmn spectr of fresh trget, PLD nd TVA films. The colours of the Rmn lines corresponding to PZT nd component oxides re irrespective to the curves colours ) Comprison etween the Rmn spectr on the lted zone of the trget nd on its fresh surfce. It is ovious tht oth deposition techniques resulted in films with high PZT contents [18]. However, shift of the lines towrd higher frequency is noticed. This is consequence of the increse of the force constnts owing to the volume contrction within the nnoprticles. Thus, in the TVA smples where the nnoprticle size is lrger thn in PLD films the Rmn shift is slightly greter [19]. The sence of P oxides lines in the spectr of fresh trgets long with the presence of most PZT lines, ZrO 2 nd TiO 2 lines mkes witness of n insufficient PO 2 excess t the trget preprtion. This ffirmtion is lso supported through the EDS nlysis of the rw, evported nd lted trgets. Rmn mesurements crried out in the lted zone of the trget

5 (see fig. 2 ) reveled n interesting effect of the lser-cermic trget interction s shown in fig.4: it ppers tht the ltion process significntly dvnces the PZT synthesis. Therefore, we elieve tht n idel wy to otin homogeneous PZT films would e to prepre cermic trgets from PO 2, ZrO 2 nd TiO 2 nnopowders nd lser - nnel them efore ny deposition process Conclusions Films with n verge thickness of 100nm were deposited y TVA nd PLD techniques on Si sustrtes held t 450 o C, from cermic trgets mde of PO 2, ZrO 2 nd TiO 2 nnopowders mixed in stoichiometric mounts 1:1:1. Rmn spectroscopy mesurements reveled high content of PZT in smples deposited y either wy lthough lines of ZrO 2 re lso present. From XRD mesurements crystllites s lrge s 40nm re found in the TVA films, wheres in the PLD ones the verge size touches 20nm. This results in smoother surfces of the PLD films, lthough droplets in smll mounts cn still e oserved. The ltion process significntly improves the PZT synthesis t the trget s surfce. Therefore, we propose cermic trgets to e prepred from PO 2, ZrO 2 nd TiO 2 nnopowders nd lser - nneled efore ny deposition process. A lrger excess of led oxide thn in this work should e foreseen for the mixture. Acknowledgments This work ws supported from the Core Progrmme, Contrcts PN 09.39, 27N nd 27N References [1] Dmjnovic, D., Rep. Prog. Phys., 61, (1998) [2] Wng, Z. H., Mo, J. M. nd Zhu,W. G., J. Eur. Cerm. Soc. 27, (2007). [3] Jones, R. E., Mnir, P. D., Mozzmi, R., Zurcher, P., Witowski, J. Z., Lii, Y. T., Chu, P. Gillespie, S. J., Thin Solid Films,, 270, (1995). [4] Dorey, R. A. nd Whtmore, R. W., J. Electrocerm.,, 12, (2004). [5] Gehrdt, S., Seffner, L., Schlenkrich, F. nd Schonecker, A., J. Eur. Cerm. Soc. 27, (2007). [6] Dimos, D. nd Mueller, C. H., Annu. Rev. Mter. Sci.,, 28, (1998). [7] Suzuki, H., Miw, Y., Noe, T., Miyzki, H., Ot, T., Fuji, M. nd Tkhshi, M., J. Eur. Cerm. Soc. 26, (2006). [8] Hirno S I, Yogo T, Tikut K, J. Am. Cerm. Soc., 75, (1992). [9] V R Prker, S C Purndre, S P Pi, Appl. Phys. Lett., 68, (1996). [10] S.K. Pndey, A.R. Jmes, Chndr Prksh, T.C. Goel, K. Zimik, Mterils Science & Engineering B 112, (2004). [11] K. Kkimoto, H. Ohsto, H. Kkemoto, Y. Msudc, J. Eur. Cerm.Soc. 24, (2004). [12] N A Bsit, H K Kim, J. Vc. Sci. Technol. A, 13, , (1995). [13] Z Zhng, X Li, J Chen, Journl of Tinjin University, 33, , (2000). [14] W Noki, K Kzums, X Yi, Thin Solid Films, 372, , (2000). [15] D.Rslenu, V.Ionescu, G.Prodn, V.Ciupin, C.P.Lungu, C.Surdu-o, M.Osic, O.Pompilin, M.Bdulescu, A.M.Lungu, C.Ticos, V.Zroschi, L.Trupin, C.Micle, J. Optoelectron. Adv. Mter., 10(11), 3041 (2008). [16] H. Klug, L. Alexnder, X-ry diffrction procedures, John Wiley nd Sons, Inc., New York,491,(1962). [17] B. D. Cullity, Elements of X-ry Diffrction, Addison- Wesley, Reding, MA, [18] Emerson R. Cmrgo, Flvio L. Souz, nd Edson R. Leite, J. Appl. Phys. 96(4), 2169 (2004). [19] Aldon Zryck, Jn Ilczuk, Dionizy Czekj, Mterils Science, 21( 4), 439 (2003).