Bismuth iron oxide thin films using atomic layer deposition of alternating bismuth oxide and iron oxide layers

• Bismuth iron oxide thin films were grown by atomic layer deposition at 140 °C.
• The major phase formed in the films upon annealing at 500 °C was BiFeO3.
• BiFeO3 films and films containing excess Bi favored electrical charge polarization.
• Slight excess of iron oxide enhanced saturative magnetization behavior.

Bismuth iron oxide films with varying contributions from Fe2O3 or Bi2O3 were prepared using atomic layer deposition. Bismuth (III) 2,3-dimethyl-2-butoxide, was used as the bismuth source, iron(III) tert-butoxide as the iron source and water vapor as the oxygen source. The films were deposited as stacks of alternate Bi2O3 and Fe2O3 layers. Films grown at 140 °C to the thickness of 200–220 nm were amorphous, but crystallized upon post-deposition annealing at 500 °C in nitrogen. Annealing of films with intermittent bismuth and iron oxide layers grown to different thicknesses influenced their surface morphology, crystal structure, composition, electrical and magnetic properties. Implications of multiferroic performance were recognized in the films with the remanent charge polarization varying from 1 to 5 μC/cm2 and magnetic coercivity varying from a few up to 8000 A/m.