Abstract
BaTiO3 exhibits several functional properties, such as high dielectric constant, large Pockels coefficient, and strong ferroelectricity/piezoelectricity. These properties can be used for a variety of applications, such as ferroelectric tunnel junctions in non-volatile memory devices. To achieve large-scale integration of BaTiO3, however, one requires the synthesis of high-quality BaTiO3 films at low temperatures in order to be compatible with the thermal budget of electronic processes in use today. Here, we describe the synthesis of BaTiO3 thin films by molecular beam epitaxy and find that coherently strained and ferroelectric BaTiO3 can be grown at temperatures as low as 310 °C. Using reflection high energy diffraction, we demonstrate a surface mobility of BaO and TiO2 adatoms that is high enough to promote ferroelectric crystal growth at low temperatures. A clear ferroelectric polarization switching is observed using piezoresponse force microscopy. Our results pave the way toward large-scale integration of ferroelectric BaTiO3 with mainstream electronics platforms.
Highlights
Mazet et al have demonstrated the epitaxial growth of 20 nm-thick BTO films by molecular beam epitaxy (MBE) on SrTiO3/Si templates with a substrate temperature as low as 410 ○C.30
We investigate the effect of substrate temperature on the synthesis of BTO thin films and report on the structural and ferroelectric properties of BTO films grown on Nb-doped SrTiO3 (Nb: STO) substrates at temperatures ranging from 270 to 500 ○C
By reflection high-energy electron diffraction (RHEED) and x-ray diffraction (XRD), we find that epitaxial and coherently strained BTO films can be achieved for a growth temperature as low as 310 ○C
Summary
Epitaxial islands of crystalline BTO with size in the range of 5–15 nm have been observed in predominantly amorphous BTO films grown at 300 ○C by metal–organic chemical vapor deposition.29 More recently, Mazet et al have demonstrated the epitaxial growth of 20 nm-thick BTO films by molecular beam epitaxy (MBE) on SrTiO3/Si templates with a substrate temperature as low as 410 ○C.30 Growth using pulsed laser deposition allows layer-by-layer growth at lower temperatures due to high kinetic energies of the arriving species,31 but this method can lead to uncontrolled reactions at oxide–semiconductor interfaces. Ferroelectric BTO has been grown using a substrate temperature as low as 450 ○C.30 These results hint at the possibility of further lowering substrate temperature for the epitaxial growth of BTO films in the nanoscale thickness regime.
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