Depolarization mitigated in ferroelectric Hf_0.5Zr_0.5O₂ ultrathin films (< 5 nm) on Si substrate by interface engineering

(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.