ZrO2 Reduction at Low Temperature in Co-Sputtered ZrxHf1−xO2 Thin-Films

Abstract

A temperature dependent x-ray photoelectron spectroscopy (XPS) study reveals that ZrO2 reduces to metallic Zr and O at ∼ 140°C at Zr ratios of 8.38, 9.11, and 11.79 at.% in co-sputtered ZrxHf1−xO2 thin-films deposited on the silicon substrate. ZrO2 is reduced in the form of Zr metal. The oxygen evolved in this process reacts with carbon present in the film forming CO2 gas. Further, the presence of Zr in temperature treated samples at room temperature (RT) indicates the reduction as an irreversible one. Capacitance-voltage (C-V) curves depict increasing capacitance at high temperature (HT), confirms an increase in dielectric constant for all the films. The resistance obtained from Resistivity-temperature measurement offers a lower value at HT indicates partial metallization of films. Despite similar atomic radii of Zr and Hf, the stability of metastable tetragonal ZrO2 (t-ZrO2) decreases probably due to the influence of Hf present in ZrxHf1−xO2. This stabilization was ascribed to a decrease in the Zr coordination number upon the introduction of oxygen vacancies. A Less dense d band causes the formation of metallic Zr at such a low temperature. A reduction scheme for ZrO2 at low temperature is also proposed. Since the generation of metallic Zr sites at a lower temperature is a challenge to develop Zr-based catalyst, this combination may be used to design ZrHfO-based catalysts for low temperature catalytic applications.