Crystalline Phase-Controlled High-Quality Hafnia Ferroelectric With RuO₂ Electrode

Electrical and reliability characteristics of hafnia ferroelectric capacitor are influenced by a capping electrode layer which controls the type of stress and the amount of oxygen vacancy inside hafnia. Here, we present the impact of metal nitride and metal oxide electrode on the ferroelectricity of a Hf_0.5Zr_0.5O₂ (HZO) capacitor. For comparison, we employed two different top electrodes (RuO₂ and TiN) with hafnia ferroelectric layer, forming RuO₂/HZO/TiN and TiN/HZO/TiN capacitors. The RuO₂ top electrode provides additional oxygen to the HZO film, lowering the amount of oxygen vacancies in the film. From material analysis, we found that the top RuO₂/HZO interface exhibits less oxygen vacancy in comparison to the top TiN/HZO interface. In addition, for RuO₂/HZO/TiN, due to different thermal expansion coefficient between top and bottom electrodes, the HZO film experiences significant tensile stress, resulting in the high o-phase formation and remnant polarization (~ 20~μC /cm²) as compared with that of TiN/HZO/TiN capacitor (~13~μC/cm²). This article suggests an efficient solution to reduce the interfacial defects and oxygen vacancies as well as to enhance o-phase formation and ferroelectricity.