Synthesis and Characterization of BiFeO₃ Thin Films for Multiferroic Applications by Radical Enhanced Atomic Layer Deposition

Abstract

A radical-enhanced atomic layer deposition (RE-ALD) process is described for the synthesis of BiFeO3. Metalorganic precursors β-diketonate, tris­(2,2,6,6-tetramethyl-3,5-heptanedionato) iron­(III) (Fe­(TMHD)3), and Bi­(TMHD)3 are coreacted with oxygen radicals (produced by a coaxial microwave cavity) as the oxidation source. Stoichiometric BiFeO3 films were deposited on SrTiO3 (001) substrates at 210 °C and crystallized from 450 to 750 °C. The crystallinity and phases in the films were characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The BiFeO3 was determined to be phase-pure and epitaxial when annealed at 650 °C. To study the functional properties, ferroelectric switching was demonstrated using piezoresponse force microscopy (PFM), while weak ferromagnetic behavior was measured using superconducting quantum interference device (SQUID) magnetometry. The films have properties comparable to those of films grown by other methodsgrowth rates are superior in comparison to other ALD methods, demonstrating the potential of RE-ALD for the synthesis of multiferroic complex–oxide thin films.

Formation of BiFeO3 from a Binary Oxide Superlattice Grown by Atomic Layer Deposition

“…Ferroelectric switching was probed on different grains and two representative hysteretic loops for the phase and the amplitude are displayed in Figures b and c, respectively. In general, the hysteresis loops measured for the grains located higher on the surface appear very symmetric and similar to those observed in ALD‐grown epitaxial BFO films (red in Figures b,c) . However, for lower‐lying grains, an asymmetric PFM response is observed (black in Figures b,c), which might be due to the clamping effect from the proximity to the neighboring grains.…”

“…ChemPhysChem 2017ChemPhysChem , 18,1966ChemPhysChem -1970 www.chemphyschem.org ChemPhysChem 2017ChemPhysChem , 18,1966ChemPhysChem -1970 www.chemphyschem.org and the amplitude are displayed in Figures 4b and 4c,r espectively.I ng eneral,t he hysteresis loops measured for the grains located higher on the surface appear very symmetric and similar to those observed in ALD-grown epitaxialB FO films (red in Figures 4b,c). [16,17,[20][21][22] However,f or lower-lying grains, an asymmetricP FM response is observed (black in Figures 4b,c), which might be due to the clamping effect from the proximity to the neighboring grains.…”

“…Although ALD is primarily used for the growth of binary oxide films and coatings, in the last years the integration of epitaxial perovskite thin films on semiconductor substrates has been reported, making this synthesis method appealing for large‐scale deposition of complex functional oxides such as ferroelectric BaTiO 3 or BFO . The synthesis of ferroelectrically switchable BFO utilizing ALD was demonstrated for both epitaxial and polycrystalline films . Direct evidence of ferroelectricity with a remnant polarization of ≈2 μC cm −2 was first reported for a 10‐nm‐thick film grown on a LaNiO 3 (001)/SiO 2 /Si(001) substrate .…”

“…[15] The synthesis of ferroelectrically switchable BFO utilizing ALD was demonstrated for both epitaxial andp olycrystalline films. [16][17][18][19][20][21][22][23][24][25] Direct evidenceo ff erroelectricity with ar emnant polarization of % 2 mCcm À2 was first reported for a1 0-nm-thick film grown on aL aNiO 3 (001)/SiO 2 /Si(001) substrate. [19] Recently, an approach, where alterings tacks of Fe 2 O 3 and Bi 2 O 3 weredeposited, proved to provide ah igh control over the cation ratio and, hence,o ver the ferroelectric and magnetic properties of the resultingp olycrystalline BFO thin films.…”

Functional Perovskites by Atomic Layer Deposition – An Overview

“…The confirmation of multiferroicity in these films sparked the interest of several groups, and to date nine articles spanning six different deposition routes have been published . One of the most important papers was published by Marchand et al in 2016, dealing very thoroughly with the electric and magnetic properties of the films .…”