STRUCTURE ANALYSIS IN SI-DOPED HAFNIUM OXIDE FERROELECTRIC THIN FILMS

Recent macroscopic studies have shown that doped HfO₂ can possess ferroelectric (FE) and antiferroelectric (AFE) properties, as detected by polarization-electric field (P-E) hysteresis measurements. Many studies were conducted with a strong focus on application in memory devices, however, the origin of ferroelectricity and in-depth studies of device characteristics need still to be explored.

In this work, remanent polarizations up to 15 μC cm^-2 were obtained in planar metal-insulator (HfO₂)-metal capacitors fabricated on p-doped Si substrates. A bottom electrode of TiN, a Si-doped HfO₂ dielectric, and a top electrode TiN were successively deposited by atomic layer deposition. Composition- and temperature-dependent transitions to a stable ferroelectric phase in Si-doped HfO₂ thin films were studied.

Due to the polycrystalline nature of the films, as well as their extremely small thickness (~10 nm) and mixed orientation and phase composition, the structural analysis of doped HfO₂ thin films remains a challenging task. To resolve this issue, we applied the grazing incidence X-ray diffraction method to investigate structure and phase transition.

In addition, the existence of the orthorhombic phase with non-centrosymmetric space group Pbc2₁ in the 3 mol% Si-doped HfO₂ thin films was confirmed by high-resolution transmission electron microscopy. This phase is expected to be responsible for the ferroelectricity in doped HfO₂ films.