Correlation between ferroelectricity and nitrogen incorporation of undoped hafnium dioxide thin films

The ferroelectric characteristics of undoped hafnium oxide (HfO₂) in titanium nitride (TiN)/HfO₂/TiN stacks exhibited improved remanent polarization by controlling the nitrogen gas flow during TiN deposition in this work. Electrical measurements revealed that samples with a higher N₂/(Ar + N₂) ratio obtained a higher remanent polarization of approximately 10 μC/cm² at 2.5 V but exhibited a larger leakage current and less reliability. Among all the samples, the sample with a N₂/(Ar + N₂) ratio of 33% exhibited a relatively high remanent polarization of 12 μC/cm² and excellent endurance over 10⁸ cycles. Through X-ray photoelectron spectroscopy (XPS) analysis, it was observed that increasing the N₂ gas flow during TiN electrode deposition contributed to excessive N-diffusion, leading to the creation of more oxygen vacancies and subsequently to device failure. Therefore, controlling the appropriate N₂ gas flow during TiN deposition is crucial to enhance the ferroelectric characteristics of undoped HfO₂. The results of this study may be applicable to future work on nonvolatile memory applications.