A study on structural, optical, electrical and microstructural properties of thin TiOx films upon thermal oxidation: Effect of substrate temperature and oxidation temperature

Influences of both substrate temperature, Ts (∼305, 473 K) and oxidation temperature, Ta (∼623–973 K) on the structural, optical, electrical and microstructural properties of thin TiOx (x≤2) films obtained by thermal oxidation of sputtered titanium thin films have been investigated. Ts is found to be an important parameter that affects both the as deposited film morphology and phase evolution of TiOx films during oxidation. As deposited and oxidized films processed at Ta∼623 K exist in TiO form. Formation of anatase (TiO2) phase takes place at Ta∼723 K. As the Ta increases above 723 K, degree of crystallinity of the film improves and rutile (TiO2) phase appears along with anatase phase at Ta∼873 K. Further increase in the Ta enhances the contribution of rutile phase at the expense of anatase contribution. Apparent crystallite size, L, and refractive index of the TiOx (x≈2) films increase with Ta but band gap energy, Eg decreases from ∼3.4 to 3.35 eV. Scanning electron microscopic study reveals that both film densification and grain size improve with Ta. As the Ta increases above 873 K, rutile phase contribution as well as grains of the oxidized films deposited at a lower Ts grow at a faster rate than that of the TiOx films prepared at a higher Ts. Room temperature resistivity of the as deposited films is found to be dependent on Ts. Film-resistivity increases with oxidation temperature and at Ta∼723 K, resistivity of the film increases drastically. Temperature coefficient of resistivity (TCR) for all the as deposited and oxidized films processed at Ta∼623 K is found to be negative and lie between ∼1.2×10−3–2.1×10−3 K−1. Thermal activation energy, Ea, of the as deposited and oxidized (Ta∼623 K) TiOx (x≈1) films is estimated to vary over the range ∼0.015–0.027 eV. Observed change in the film electrical properties with Ta is discussed in the light of oxygen incorporation in the TiOx structure.