Ultrathin WOx interfacial layer improving the ferroelectricity and endurance of Hf0.5Zr0.5O2 thin films on polyimide

Abstract

Here we report substantial effects of inserting PVD-prepared highly-conductive ultrathin WO_x as interfacial layer in TiN/Hf_0.5Zr_0.5O₂(HZO)/TiN structure on the ferroelectricity of HZO thin films. The prepared TiN/WO_x/HZO/WO_x/TiN capacitor, exhibiting a remnant polarization (P_r) of 18.8 μC/cm² at 2 MV/cm and outstanding endurance of over 3.2×10⁹ cycles under 10⁵ Hz bipolar square field cycling. Furthermore, a scalable transfer technique, in which CVD-grown few-layered graphene thin film is used as a sacrificial layer, is developed for transferring HZO-based ferroelectric stack pre-fabricated on SiO₂/Si substrate onto a flexible polyimide (PI) membrane, with marginal loss in the ferroelectric properties of HZO. Importantly, mechanical bending testing demonstrates excellent flexibility of TiN/WO_x/HZO/WO_x/TiN stack, with robust polarization and superb endurance properties being well-maintained even after 10⁴ cycles at a small bending radius of 2 mm. Both implementing ultrathin WO_x as interfacial layers and utilizing two-dimensional materials assisted transfer technique would be of great value in the development of HfO₂-based flexible ferroelectric memory.