The Impact of Crystallinity on Ferroelectric Properties of Epitaxial Rhombohedral Hf_0.5Zr_0.5O₂ Films

Ferroelectric hafnium oxide is of great interest in the semiconductor industry due to its complementary metal-oxide-semiconductor compatibility and scalability. It has potential to be used as actuator, sensors, transducers, memories, etc. Out of all the dopants studied, zirconium doped hafnium oxide, Hf_0.5Zr_0.5O₂ (HZO), has been the most promising and widely investigated composition with reported remanent polarisation (P_r) of ~ 20 μC/cm2 and coercive field (E_c) of ~ 1 MV/cm. However, there are limitations with ALD-grown ferroelectric HZO films in terms of wake-up effect, endurance and tuning of P_r and E_c for specific application such as ferroelectric random-access memory (FeRAM), ferroelectric field effect transistor (FeFET), negative capacitance field effect transistor (NCFET), and many more. In this work, model systems of HZO films were deposited by pulsed laser deposition (PLD) in which the epitaxial rhombohedral ferroelectric phase was stabilised. All the films show wake-up free ferroelectric behaviour with P_r > 7 μC/cm². With increase in laser fluence from 0.5 to 1.3 J/cm², EC increased from ~ 2.7 MV/cm to ~ 3.3 MV/cm. In order to understand the origin of such change in ferroelectric properties, we separate out individual influences of O content, strain and microstructure via x-ray photoelectron spectroscopy, x-ray diffraction, and scanning tunnelling electron microscopy.