The effect of post-process annealing on optical and electrical properties of mixed HfO2\u2013TiO2 thin film coatings

Agata Obstarczyk,Jerzy Morgiel,Damian Wojcieszak,Jaroslaw Domaradzki,Danuta Kaczmarek,Michal Mazur,Tomasz Kotwica

doi:10.1007/s10854-019-00938-5

Abstract

In this paper a comparison of electrical and optical properties of mixed hafnium-titanium oxides is described. Thin films were deposited with the use of the magnetron co-sputtering method. For further analysis (Hf0.52Ti0.48)Ox and (Hf0.29Ti0.71)Ox coatings, which were amorphous directly after the deposition process, were chosen,. Moreover, post-process annealing was also performed in order to compare the electrical and optical properties of amorphous and nanocrystalline thin films with the same material composition. It was found that the phase transition from amorphous to orthorhombic HfTiO4 occurred in the case of (Hf0.52Ti0.48)Ox coating at 650 °C. In turn, the phase transition to TiO2-anatase was observed at the temperature of 600 °C in the case of (Hf0.29Ti0.71)Ox thin film. The leakage current for both amorphous coatings was in the range of 10−7–10−8 A/cm2. After additional annealing and phase transition, the leakage current slightly decreased for (Hf0.29Ti0.71)Ox thin film, while in the case of (Hf0.52Ti0.48)Ox sample the resistance switching effect was observed. The dielectric constant was equal to 24 and 25 for amorphous (Hf0.52Ti0.48)Ox and (Hf0.29Ti0.71)Ox films, respectively. However, after the phase transition it decreased to 15 for (Hf0.52Ti0.48)Ox and increased to 51 for (Hf0.29Ti0.71)Ox film. The results of optical studies showed that amorphous thin films were well transparent in a visible light range with an average transparency of ca. 85%. After the phase transition to HfTiO4-orthorhombic and TiO2-anatase, a slight decrease in the transparency level by 3% and a redshift of the cut-off wavelength was observed. Moreover, additional annealing caused small changes of the optical band gap energy, refractive index and extinction coefficient.

Highlights

Transition metal oxides are the focus of attention due to their outstanding chemical stability and excellent physical properties
Hafnium dioxide (HfO2) has received significant attention in the recent years as a potential replacement for SiO2 used as the gate dielectric material in the complementary metal oxide semiconductor (CMOS) technology [2, 3]. HfO2 is extremely attractive due to its high dielectric constant, large band offset (∆Ec ~ 1.5 eV) and
Mixed oxide thin films based on HfO2 and TiO2 have attracted a lot of attention due to their potential application in, e.g. metal oxide semiconductor devices, thin film transistors, optical and protective coatings or memory devices [39,40,41,42]

Summary

Introduction

Transition metal oxides are the focus of attention due to their outstanding chemical stability and excellent physical properties They are suitable for several industrial applications in the field of electronics and optoelectronics [1]. Hafnium dioxide (HfO2) has received significant attention in the recent years as a potential replacement for SiO2 used as the gate dielectric material (high-k oxide) in the complementary metal oxide semiconductor (CMOS) technology [2, 3]. Mixed oxide thin films based on HfO2 and TiO2 have attracted a lot of attention due to their potential application in, e.g. metal oxide semiconductor devices, thin film transistors, optical and protective coatings or memory devices [39,40,41,42]. Electrical and optical properties of amorphous and nanocrystalline samples were compared

Experimental

Results and discussion

Conclusion