A dielectric film containing Zr--Sn--Ti--O formed by atomic layer deposition using a TiI.sub.4 precursor and a method of fabricating such a dielectric film produce a reliable dielectric layer having an equivalent oxide thickness thinner than attainable using SiO.sub.2. Depositing titanium and oxygen onto a substrate surface by atomic layer deposition using a TiI.sub.4 precursor, depositing zirconium and oxygen onto a substrate surface by atomic layer deposition, and depositing tin and oxygen onto a substrate surface by atomic layer deposition form the Zr--Sn--Ti--O dielectric layer. Dielectric films containing Zr--Sn--Ti--O formed by atomic layer deposition using TiI.sub.4 are thermodynamically stable such that the Zr--Sn--Ti--O will have minimal reactions with a silicon substrate or other structures during processing.