Atomic layer deposition of LixTiyOz thin films

Abstract

Atomic layer deposition (ALD) was employed to deposit ternary films of Li_xTi_yO_z. The film growth at a deposition temperature of 225 °C was studied using both titanium tetra-isoropoxide (Ti(OⁱPr)₄) and titanium tetrachloride (TiCl₄) as titanium precursors. Lithium tert-butoxide (LiO^tBu) was applied as the lithium source and water was used as the oxygen source for all metal precursors. The type of titanium precursor chosen strongly affected film growth: with TiCl₄ the resulting Li_xTi_yO_z films were highly air-sensitive and the lithium concentration was low, whereas with Ti(OⁱPr)₄ the films were relatively stable in air and with a lithium content which was easily controlled over a wide range. Film characterization indicated that part of the lithium in the film migrated onto the surface and formed carbonates. Films with suitable lithium contents crystallized into the spinel Li₄Ti₅O₁₂ structure upon post-deposition annealing.