Formation of orthorhombic (Zr,Ta)O₂ in thin Zr-Ta-O films

The formation of orthorhombic (Zr,Ta)O2 was found in annealed thin Zr-Ta-O films with various tantalum concentrations deposited by co-sputtering a ZrO2 target and a mixed ZrO2/Ta2O5 target. In the as-deposited state, all films were amorphous. After annealing, tetragonal (Zr,Ta)O2 for [Ta]/([Ta]+[Zr]) < 0.19 and orthorhombic (Zr,Ta)O2 for [Ta]/([Ta]+[Zr]) > 0.19 were formed. Thin films with excess of tantalum ([Ta]/([Ta]+[Zr])> 0.5) decomposed into two orthorhombic phases upon crystallization: (Zr,Ta)O2 and tantalum-rich (Ta,Zr)2O5. The Rietveld analysis of Xray diffraction patterns revealed that the crystal structure of (Zr,Ta)O2 can be described with the non-centrosymmetric space group Pbc21. The broad range of tantalum concentrations, in which orthorhombic (Zr,Ta)O2 is formed as a single crystalline phase, is promising for the use of this
compound in ferroelectric field effect transistors.