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Definition of optimum precursors for MOCVD of SBT

Insights of the mass transport properties and deposition kinetics have been obtained for various SrBi2Ta2O9 precursors. The obtained information combined with available literature data can be used to chose suited precursor combination for use in SBT processes. Investigated precursors have been Sr(tmhd)2, Sr(tmhd)2tetraglyme ( H-tmhd = 2,2’,6,6’-tetramethylheptandione ), Sr(tmhd)2pmdeta ( pentamethyldiethyltriamine ) and Sr(hfac)2tetraglyme (H-hfac= 1,1,1,5,5,5-hexafluoropentane-2,4-dione) as Sr sources, Bi(C6H5)3 and Bi(tmhd)3 as Bi sources and Ta(OC2H5)5.

Not fluorinated Sr precursors show low thermal stability and decompose upon sublimation. Beta-diketonate adducts with neutral ligands loose easily these ligands upon sublimation. This behaviour determines large similarities among the deposition process of Sr(tmhd)2, Sr(tmhd)2tetraglyme and Sr(tmhd)2pmdeta.

The fluorinated Sr(hfac)2tetraglyme precursor possess higher thermal stability upon sublimation and good mass-transport properties. It does not dissociate upon sublimation.

As regards the deposition process under O2, not fluorinated beta-diketonate leads to oxide and carbonate mixtures, while Sr(hfac)2tetraglyme to the formation of fluoride. Carbon or fluorine contaminations are efficiently eliminated in the annealing step in both cases.

Comparisons between Bi(tmhd)3 and Bi(C6H5)3 as Bi sources showed that Bi(C6H5)3 possess higher thermal stability during sublimation/vaporization and mass transport. The study of the MOCVD processes has shown that both precursors lead to uniform film of bismuth oxides. MOCVD processes from Bi(C6H5)3 requires temperature higher than 350°C and the presence of oxygen.

The high activation energy of Sr(hfac)2tetraglyme and Bi(C6H5)3 (about 100kJ/mol), compared to the Ta precursor, makes the choice of the deposition temperature a critical point of the multicomponent MOCVD process. By contrast, Sr(tmhd)2pmdeta and Bi(tmhd)3 complexes posses similar activation energies compared to Ta precursor. This characteristic allows a larger flexibility in the choice of the SBT deposition temperature, thus making not-fluorinated beta-diketonate interesting precursors despite their low thermal stability during vaporization. Therefore, the results on the MOCVD behaviour of single precursors can be used for the optimisation of MOCVD processes adopting various precursor combinations.

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Universita di Catania
V.le A. Doria 6
95124 Catania
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