The impact of oxygen content in the Ru electrode, grown using atomic layer deposition on ferroelectricity in Hf_0.5Zr_0.5O₂ film is investigated. The oxygen content in Ru can be modulated by simply adjusting the deposition temperature from 210 ℃ to 300 ℃. Higher oxygen content in Ru reduces the oxygen vacancy concentration in subsequently grown Hf_0.5Zr_0.5O₂ film, thereby mitigating the wake-up effect. However, the monoclinic phase fraction increased with decreasing Ru deposition temperature, resulting in a decrease in remanent polarization. The decreased oxygen vacancy concentration by oxygen diffusion from Ru electrode deposited at 210 ℃ could decrease the leakage current density compared to that grown at higher temperatures. Nonetheless, the switching endurance of Hf_0.5Zr_0.5O₂ film grown on Ru deposited at 210 ℃ was shorter than those on Ru deposited at 300 ℃ by 2 order of magnitude, being attributed to the oxygen diffusion caused interfacial damages. This observation suggests that the interfacial redox reactions between the electrode and Hf_0.5Zr_0.5O₂ critically influence defect concentration, polymorphism, and the resulting ferroelectricity when using an atomic layer deposited Ru electrode to examine the impact of interfacial redox chemistry.

This study proposes a novel approach to achieving highly reliable, low-voltage polarization switching of ferroelectric Hf_0.5Zr_0.5O₂ (HZO) thin films using polymorph- and orientation-controlled W electrodes ((111)-textured α-W and (200)-textured β-W) by adjusting the sputtering conditions. We demonstrated the formation of (111) and (002)/(020)-textured HZO films on the (111)-textured α-W and (200)-textured β-W electrodes, respectively. Under a low-voltage pulse of 1.2 V (1.5 MV/cm), α-W/HZO/α-W and β-W/HZO/β-W capacitors exhibited double-remanent polarization (2P_r) values of 29.23 μC/cm² and 25.16 μC/cm², which were higher than that of the TiN/HZO/TiN capacitor by 33% and 14%, respectively, and a high endurance of 10⁹ cycles without hard-breakdown. The differences in the ferroelectric properties and switching kinetics were understood based on the polymorphism and texture of the HZO films influenced by electrode materials.

(Hf,Zr)O₂ offers considerable potential for next-generation semiconductor devices owing to its nonvolatile spontaneous polarization at the nanoscale. However, scaling this material to sub-5 nm thickness poses several challenges, including the formation of an interfacial layer and high trap concentration. In particular, a low-k SiO₂ interfacial layer is naturally formed when (Hf,Zr)O₂ films are directly grown on a Si substrate, leading to high depolarization fields and rapid reduction of the remanent polarization. To address these issues, we conducted a study to significantly improve ferroelectricity and switching endurance of (Hf,Zr)O₂ films with sub-5 nm thicknesses by inserting a TiO₂ interfacial layer. The deposition of a Ti film prior to Hf_0.5Zr_0.5O₂ film deposition resulted in a high-k TiO₂ interfacial layer and prevented the direct contact of Hf_0.5Zr_0.5O₂ with Si. Our findings show that the high-k TiO₂ interfacial layer can reduce the SiO₂/Si interface trap density and the depolarization field, resulting in a switchable polarization of 60.2 μC/cm² for a 5 nm thick Hf_0.5Zr_0.5O₂ film. Therefore, we propose that inserting a high-k TiO₂ interfacial layer between the Hf_0.5Zr_0.5O₂ film and the Si substrate may offer a promising solution to enhancing the ferroelectricity and reliability of (Hf,Zr)O₂ grown on the Si substrate and can pave the way for next-generation semiconductor devices with improved performance.