Effect of metal Hf interlayer on the electric properties of HfO2 films deposited by reactive magnetron sputtering

Ferroelectric hafnium oxide (HfO2) thin film has been widely studied as a promising material candidate for microelectronic devices. In this paper, HfO2/Hf/HfO2 stacked films were deposited by reactive magnetron sputtering to investigate the effects of metal Hf on the phase transition and electric properties. An interesting phenomenon is that HfO2 film inserted with a thin layer of metal Hf exhibits ferroelectricity after high-field cycling (wake-up). The generation of ferroelectricity is due to a region in HfO2 film with a gradient distribution of oxygen vacancies resulting in the formation of orthorhombic HfO2, which is caused by the oxidation of metal Hf in HfO2 film. Inserted with 0.2-nm-thick metal Hf layer, the stacked film shows the coercive field of 3.4 MV/cm and remanent polarization of 4.2 mu C/cm(2), respectively. An increase in the Hf layer thickness from 0.2 to 1.5 nm causes the leakage current density of the stacked film increasing from 8.2 x 10(-6) to 6.2 x 10(-4) A/cm(2). The results provide a strong evidence for the important role of inhomogeneous oxygen vacancies played in introduction of the ferroelectricity of HfO2 film.