Depolarization mitigated in ferroelectric Hf _0.5Zr _0.5O ₂ ultrathin films (< 5 nm) on Si substrate by interface engineering

Abstract

Hf,Zr)O 2 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 SiO 2 interfacial layer is naturally formed when (Hf,Zr)O 2 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)O 2 films with sub-5 nm thicknesses by inserting a TiO 2 interfacial layer. The deposition of a Ti film prior to Hf 0.5 Zr 0.5 O 2 film deposition resulted in a high-k TiO 2 interfacial layer and prevented the direct contact of Hf 0.5 Zr 0.5 O 2 with Si. Our findings show that the high-k TiO 2 interfacial layer can reduce the SiO 2 /Si interface trap density and the depolarization field, resulting in a switchable polarization of 60.2 μC/cm 2 for a 5 nm thick Hf 0.5 Zr 0.5 O 2 film. Therefore, we propose that inserting a high-k TiO 2 interfacial layer between the Hf 0.5 Zr 0.5 O 2 film and the Si substrate may offer a promising solution to enhancing the ferroelectricity and reliability of (Hf,Zr)O 2 grown on the Si substrate and can pave the way for next-generation semiconductor devices with improved performance.