Temperature and ambient atmosphere dependent electrical characterization of sputtered IrO₂/TiO₂/IrO₂ capacitors

Abstract

Titanium dioxide (TiO₂) is a high-performance material for emerging device applications, such as in resistive switching memories, in high-k capacitors, or, due to its flexoelectricity, in micro/nano-electro-mechanical systems. Enhanced electrical properties of TiO₂ are ensured, especially by a careful selection of the bottom electrode material. Iridium dioxide (IrO₂) is an excellent choice, as it favors the high-k rutile phase growth of TiO₂. In this study, we introduce the fabrication of IrO₂/TiO₂/IrO₂ capacitors and thoroughly characterize their electrical behavior. These capacitors show a dielectric constant for low temperature sputtered TiO₂ of ∼70. From leakage current measurements, a coupled capacitive-memristive behavior is determined, which is assumed due to the presence of a reduced TiO₂-x layer at the IrO₂/TiO₂ interface observed from transmission electron microscopy analyses. The memristive effect most probably originates from trapping and detrapping of electric charges in oxygen vacancy defects, which themselves can be generated and annihilated through an applied electric field, subsequently changing the resistance of the capacitor. The electric degradation type is identified as a filament-forming mechanism. Additionally, the temperature dependence of the leakage current is measured, demonstrating that the temperature behavior is strongly influenced by the ambient atmosphere. The latter dependency leads to the hypothesis that the oxygen evolution reaction of water incorporated in the IrO₂/TiO₂ interface passivates vacancies, thus significantly impacting the vacancy density in TiO₂ and, as a further consequence, the electrical performance.