Characteristics of the surface layer of barium strontium titanate thin films deposited by laser ablation

Abstract

Ba 0.5 Sr 0.5 TiO 3 ͑BST͒ thin films grown on Si by an in situ ultraviolet-assisted pulsed laser deposition ͑UVPLD͒ technique exhibited significantly higher dielectric constant and refractive index values and lower leakage current densities than films grown by conventional PLD under similar conditions. X-ray photoelectron spectroscopy ͑XPS͒ investigations have shown that the surface layer of the grown films contained, besides the usual BST perovskite phase, an additional phase with Ba atoms in a different chemical state. PLD grown films always exhibited larger amounts of this phase, which was homogeneously mixed with the BST phase up to several nm depth, while UVPLD grown films exhibited a much thinner ͑ϳ1 nm͒ and continuous layer. The relative fraction of this phase was not correlated with the amount of C atoms present on the surface. Fourier transform infrared spectroscopy did not find any BaCO 3 contamination layer, which was believed to be related to this new phase. X-ray diffraction measurement showed that although PLD grown films contained less oxygen atoms, the lattice parameter was closer to the bulk value than that of UVPLD grown films. After 4 keV Ar ion sputtering for 6 min, XPS analysis revealed a small suboxide Ba peak for the PLD grown films. This finding indicates that the average Ba-O bonds are weaker in these films, likely due to the presence of oxygen vacancies. It is suggested here that this new Ba phase corresponds to a relaxed BST surface layer.

Dielectric properties of BaMg1∕3Nb2∕3O3 doped Ba0.45Sr0.55Tio3 thin films for tunable microwave applications

“…21 Though insignificant, the higher -phase fraction for undoped film shows a Ti poor surface as well as higher oxygen vacancy which exhibits itself through the increase of dielectric loss and LC. 26,29,30 On the other hand, the peak positions for the undoped film (Ba3d 5=2 , Ba3d 3=2 ) and (Ba3d 5=2 , Ba3d 3=2 ) are comparable with what has been reported by others, [24][25][26][27][28] but the doping has introduced a surface core level shift towards higher binding energy by about 0.4 eV. The spin-orbit coupling distance (Ba3d 5=2 !…”

“…[24][25][26][27][28] The -phase is associated to Ba atoms in BST perovskite 24 while the -phase is coupled with Ba atom in BST nonperovskite environment, such as carbonates, 27 oxides, 28 and relaxed BST phases due to oxygen vacancy and residual defects. 24,26 Moreover, in Ref. 25 after performing XPS analysis at variable emission angles, the -phase was found to be Ti-poor, Ba and Sr rich nonperovskite structure dominant on the surface of the film than the bulk.…”

Photoluminescence at room temperature in amorphous SrTiO3 thin films obtained by chemical solution deposition

“…There is much interest in the areas of science and technology in perovskite-type structured compounds with the chemical ABO 3 formula (A and B are cations while O is the oxygen anion), owing to their wide range of electronic applications [1][2][3][4]. Within this class of compounds, SrTiO 3 and BaTiO 3 , in their crystalline form, display a semiconductor behavior.…”

Plasma deposition of thin layers containing titanium and barium with the use of DBD

“…Materials such as BaTiO 3 , due to their high dielectric constant [1][2][3][4][5][6][7][8], are commonly used in microelectronic devices such as multilayer ceramic capacitors [1,[4][5][6][7][8][9][10][11][12], random-access memories (RAM) [2,4,5,7,11,12], optoelectronic devices [1,5,7,10] or sensors [6,13,14].…”