Enhanced Dielectric Properties in SrTiO₃/BaTiO₃ Strained Superlattice Structures Prepared by Atomic-Layer Metalorganic Chemical Vapor Deposition

Abstract

We describe the investigation of epitaxial SrTiO 3 /BaTiO 3 strained superlattice films prepared by an atomic-layer metalorganic chemical vapor deposition (ALMOCVD) method. Transmission electron microscopy (TEM) observation shows that the multilayered structure is globally uniform and that the interfaces formed between the different layers are of low roughness. Xray diffraction (XRD) analysis reveals a series of satellite peaks on both sides of the zero-order peak, a characteristic feature of the superlattice structure. Careful analysis of XRD and HRTEM images suggests that the tetragonality in the superlattice films is enhanced; this is presumably due to strain caused by heteroepitaxial growth. Dielectric constants of the superlattice films increase with decreasing period of the superlattice structure. An equivalent oxide thickness of 0.8 nm is obtained. These results demonstrate that the ferroelectricity of SrTiO 3 /BaTiO 3 superlattice films can be controlled artificially by fixing the period of the superlattice.

Structural characteristics of epitaxial BaTiO3/LaNiO3 superlattice

“…The position of the main peak in the ͑002͒ CTR spectra is determined by the average c-axis length of the superlattice. 12 The main peak position of superlattice with stacking periodicity below 16 nm shifts toward a low L index comparing to the weighted mean of the c-axis length of bulk BTO and LNO films (Lϭ1.968) indicating the elongation of BTO lattice along ͓00L͔ by the heteroepitaxial strain in superlattice, although the c-axis parameter of the individual sublayers cannot be obtained directly from the CTR spectra due to the coherent interference from the sublayer structure. 17 Since satellite peaks appear in the vicinity of the main peak at an angle interval corresponding to the superlattice period, the period of superlattice (t BTO ϩt LNO ) can be calculated from the angle intervals between satellite peaks following the formula 18 below,…”

“…[7][8][9] It has been shown that the superlattice of BaTiO 3 /SrTiO 3 ͑BTO/STO͒ has a significant dielectric enhancement. [10][11][12] For the superlattice materials, composite effect from individual compounds and their interface usually dominates the material property. However, in BTO/STO superlattice system, the role of interface was rarely characterized and the contribution of individual compounds on the dielectric enhancement is ambiguous.…”

Characteristics of sputter-deposited BaTiO3/SrTiO3 artificial superlattice films on an LaNiO3-coated SrTiO3 substrate

“…It is shown that the dielectric constant increases with decreasing period of the superlattices. This is because the polarization is effected by the stress due to the mismatching of different layers in the superlattice [33]. This suggests also the dielectric constant can be controlled artificially by fixing the period of the superlattice with RF sputtering.…”

Chemically Conformal ALD of SrTiO[sub 3] Thin Films Using Conventional Metallorganic Precursors

“…There are several reports on the ALD of STO, 16,17 BaTiO 3 ͑BTO͒, 16 and nanolaminated STO/BTO 18,19 films. Among them, the nanolaminated STO/BTO ALD process is performed at very high temperature ͑Ͼ600°C͒, which thermally decomposes the metallorganic precursors, bis͑2,2,6,6-tetramethyl-3,5-heptanedionato͒Sr ͓Sr͑C 11 H 19 O 2 ͒ 2 , Sr͑thd͒ 2 ͔ and Ti-tetraisopropoxide ͓Ti͑Oi-C 3 H 7 ͒ 4 , TTIP͔.…”