Study on Metal Bottom Electrode Screening and Oxygen-Engineered TiN for Enhanced Ferroelectricity in HZO Capacitors

Abstract

Ferroelectric Hf0.5Zr0.5O2 (HZO) thin films are promising for next-generation non-volatile memories because they maintain robust polarization at sub-10-nm thicknesses and are compatible with CMOS technology. However, their ferroelectric properties are strongly affected by extrinsic factors such as electrode materials, interfacial layers, and oxygen vacancy distribution, which makes it difficult to simultaneously optimize remanent polarization, switching voltage, and endurance at the device level. In particular, the bottom electrode not only determines the electrical boundary conditions but also influences the crystallographic phase stability and texture of HZO, while additional oxygen engineering of the electrode can further modify the interfacial chemistry. Here we suggest that selecting an optimal bottom electrode and then finely controlling its oxidation state is a key strategy to enhance and balance the ferroelectric properties of HZO capacitors. Thus, we first performed a systematic bottom electrode screening using Mo, Ni, W, and TiN in MFM capacitors with 10-nm ALD HZO, and identified TiN as the most advantageous electrode, showing the highest remanent polarization and superior endurance, supported by an increased o-phase fraction associated with its strong (111) texture. Building on this, we experimentally engineered TiN by varying the O2 flow during HSC sputtering and analytically correlated the resulting TiO2/Ti–O–N interfacial layer and oxygen vacancy distribution with polarization–voltage characteristics and endurance behavior. The optimized condition with moderate oxidation (10 sccm O2) enabled reduced switching voltage and stable cycling compared to under- or over-oxidized electrodes, which suffer from insufficient o-phase formation or excessively insulating TiO₂ layers. This approach is meaningful in that it demonstrates a practical, materials- and interface- centered route to rapidly tune and predict HZO ferroelectric performance using electrode selection and oxygen engineering, providing clear insight into how bottom-electrode structure and chemistry govern the macroscopic properties of ferroelectric capacitors.