Ultrathin WO 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 0.5 Zr 0.5 O 2 (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/cm 2 at 2 MV/cm and outstanding endurance of over 3.2 × 10 9 cycles under 10 5 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 SiO 2 /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 10 4 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 HfO 2 -based flexible ferroelectric memory. • Ultrathin WO x interfacial layer is proven highly effective to improve the ferroelectricity of HZO thin films. • TiN/WO x /HZO/WO x /TiN capacitors exhibit outstanding endurance up to 3.2 × 10 9 cycles under 10 5 Hz square field. • A graphene-assisted damage-free transfer of annealed HZO-based ferroelectric stack onto PI is successfully developed. • Flexible HZO devices demonstrate superior ferroelectricity and flexibility, outperforming other reported HZO structures.

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