Thermal properties of TiO2 films grown by atomic layer deposition

Abstract

We study the thermal properties of amorphous TiO2 thin films of various thicknesses t, grown by atomic layer deposition. The thermo-optic coefficient dn/dT and the temperature coefficient dρ/dT of film density ρ are determined from ellipsometric data in wavelength range 380<λ<1800nm with the Cauchy model and the Lorentz–Lorenz relation. It is found that dn/dT exhibits negative values for films with t<150nm and positive values for thicker films, while no significant changes in the two coefficients take place if t<200nm. A qualitative physical explanation based on porosity of the thin films is suggested. Films with t=60nm are illustrated in detail at λ=640nm: the room-temperature values of the coefficients are found to be dn/dT=−3.1×10−5°C−1 and dρ/dT=−4.8×10−5gcm−3°C−1.