Electrical and material characterizations of high-permittivity Hf _x Ti _1-x O ₂ gate insulators

High-permittivity hafnium titanate (Hfx Ti1-x O2) films of various compositions have been investigated. Chemical-vapor deposited thin films have well-controlled composition and a smooth surface. Thicker films show large, highly anisotropic grains with their long axis in the plane of the film. Electrical measurements showed that the interfacial layer equivalent oxide thickness (EOT) decreases linearly with increasing Hf content. Electron energy-loss spectroscopy in scanning transmission electron microscopy indicates that the interfacial layer is primarily SiO2. In the composition range of 0.3<x<0.5, the permittivity of the high- κ films increases linearly with increasing Ti content. For values of x<0.3, the film's permittivity is close to that of pure HfO2 (∼20), while for Ti-rich films the permittivity is close to that of pure TiO2 (∼50). For films with a physical thickness less than 10 nm, the leakage current decreases as Ti increases for a fixed EOT.