Ferroelectric HfO 2 is a promising material for new memory devices, but significant improvement of its important properties is necessary for practical application. However, previous literature shows that a dilemma exists between polarization, endurance and retention. Since all these properties should be simultaneously high, overcoming this issue is of the highest relevance. Here, we demonstrate that high crystalline quality sub-5 nm Hf 0.5 Zr 0.5 O 2 capacitors, integrated epitaxially with Si(001), present combined high polarization (2P r of 27 µC cm −2 in the pristine state), endurance (2P r > 6 µC cm −2 after 10 11 cycles) and retention (2P r > 12 µC cm −2 extrapolated at 10 years) using the same poling conditions (2.5 V). This achievement is demonstrated in films thinner than 5 nm, thus opening bright possibilities in ferroelectric tunnel junctions and other devices.This journal is

Doping ferroelectric Hf 0.5 Zr 0.5 O 2 with La is a promising route to improve endurance. However, the beneficial effect of La on the endurance of polycrystalline films may be accompanied by degradation of the retention. We have investigated the endurance-retention dilemma in La-doped epitaxial films. Compared to undoped epitaxial films, large values of polarization are obtained in a wider thickness range, whereas the coercive fields are similar, and the leakage current is substantially reduced. Compared to polycrystalline La-doped films, epitaxial La-doped films show more fatigue but there is not significant wake-up effect and endurance-retention dilemma. The persistent wake-up effect common to polycrystalline La-doped Hf 0.5 Zr 0.5 O 2 films, is limited to a few cycles in epitaxial films. Despite fatigue, endurance in epitaxial La-doped films is more than 10 10 cycles, and this good property is accompanied by excellent retention of more than 10 years. These results demonstrate that wake-up effect and endurance-retention dilemma are not intrinsic in La-doped Hf 0.5 Zr 0.5 O 2 .

Systematic studies on polycrystalline Hf1-xZrxO2 films varying Zr content show that HfO2 films are paraelectric (monoclinic). If Zr content is increased films become ferroelectric (orthorhombic) and after antiferroelectric (tetragonal). Whereas HfO2 shows very good insulating properties and it is used in metaloxide-semiconductor field-effect devices, ZrO2 shows good piezoelectric properties, but it is antiferroelectric. In between, Hf0.5Zr0.5O2 shows good ferroelectric properties at expenses of poorer insulating and piezoelectric properties than HfO2 and ZrO2, respectively. Here, we explore ferroelectric, insulating and piezoelectric properties of a series of epitaxial films of Hf1-xZrxO2 with different composition. We show that epitaxial growth enhances the stabilization of the ferroelectric behaviour compared with polycrystalline films in a wider compositional range and up to around 1000 K. This allows, in epitaxial ZrO2 films ferroelectricity coexists with better piezoelectric and insulating properties than Hf0.5Zr0.5O2 and in HfO2 epitaxial films ferroelectricity coexists with better insulating properties than Hf0.5Zr0.5O2. In both cases, the ferroelectric endurance is poorer than for Hf0.5Zr0.5O2.

The metastable orthorhombic phase of Hf0.5Zr0.5O2 (HZO) can be stabilized in thin films on La0.67Sr0.33MnO3 (LSMO) buffered (001)-oriented SrTiO3 (STO) by an intriguing epitaxy that results in (111)-HZO oriented growth...

No abstract