Epitaxial growth of high-k Ba_xSr_1−xTiO₃ thin films on SrTiO₃ (001) substrates by atomic layer deposition Available to Purchase

Atomic layer deposition (ALD) offers a viable route for the growth of thin and conformal films over 3D topographies and is becoming attractive as a method to grow films thin enough, and with sufficient dielectric constants (k), for the fabrication of next-generation dynamic random memories. The authors used ALD to grow thin (≤15 nm) Ba_xSr_1 − xTiO₃ (BST) films that are epitaxially integrated to SrTiO₃ (001) (STO) and Nb-doped SrTiO₃ (001) (Nb:STO). Films of three compositions, which are x ∼ 0.7, 0.5, and 0.3, and thicknesses of 7.8–14.9 nm were grown at 1.05 Torr and 225 °C using barium bis(triisopropylcyclopentadienyl), strontium bis(triisopropylcyclopentadienyl), titanium tetraisopropoxide, and H₂O. Film compositions were controlled by changing cycle ratios (Ba:Sr, Ba:Ti, and Sr:Ti) and confirmed by in situ x-ray photoelectron spectroscopy. Films were amorphous as-deposited and required postdeposition vacuum annealing at 650–710 °C to crystallize. Epitaxy was confirmed with x-ray diffraction and transmission electron microscopy. Only BST (00l) out-of-plane diffraction signals were detected. Capacitance-voltage (C-V) measurements revealed that BST thin films grown by ALD have dielectric constant values ranging from 210 for Ba_0.71Sr_0.26TiO₃ to 368 for Ba_0.48Sr_0.43TiO₃.