Avoiding water reservoir effects in ALD of functional complex alkali oxides by using O3 as the oxygen source

Toxic Pb-containing piezo-, pyro- and ferroelectrics continue to dominate the market even though they were banned from use in consumer products more than a decade ago. There is a strong need for sustainable alternatives, but the lack of facile synthesis routes for thin films exhibiting suitable functional properties have limited the transition from Pb workhorse materials like Pb(Zr,Ti)O3 and Pb(Mg,Nb)O3 - PbTiO3. Atomic layer deposition has proven capable of the deposition of possible successors, such as LiNbO3, (K,Na)NbO3 and K(Ta,Nb)O3, albeit with limited control due to water reservoir effects resulting from the hygroscopicity of intermediate products. In this article, we show that replacing H2O with O3 in the deposition of complex alkali oxides provides an alternative and much more controlled process. We exemplify this by deposition of crystalline K(Ta,Nb)O3 with high compositional control and over a larger composition range than previously reported. This opens new doors to a simplified synthesis of polar functional lead-free alternatives.