Large Remnant Polarization in a Wake-Up Free Hf_0.5Zr_0.5O₂ Ferroelectric Film through Bulk and Interface Engineering

Abstract

A wake-up free Hf0.5Zr0.5O2 (HZO) ferroelectric film with the highest remnant polarization (Pr) value to-date was achieved through tuning of the ozone pulse duration, the annealing process, and the metal/insulator interface. The ozone dosage during the atomic layer deposition of HZO films appears to be a crucial parameter in suppressing the mechanisms driving the wake-up effect. A tungsten capping electrode with a relatively low thermal expansion coefficient enables the induction of an in-plane tensile strain, which increases the formation of the orthorhombic phase while decreasing the formation of the monoclinic phase during the cooling step of the annealing process. Therefore, increasing the annealing temperature TA followed by rapid cooling to room temperature resulted in a substantial increase in the 2Pr value (≈ 64 µC/cm 2 ). However, the leakage current increased considerably, which can affect the performance of metal-insulator-metal (MIM) devices. To reduce the leakage current while maintaining the mechanical stress during thermal annealing, a 10 nm Pt layer was inserted between the W/HZO bottom interface. This resulted in a ~ 20-fold decrease in the leakage current while the 2Pr value remained almost constant (~ 60 µC/cm 2 ). The increase in barrier height at the Pt/HZO interface compared to that of the W/HZO interface coupled with the suppression of the formation of interfacial oxides (WOx) by the introduction of a Pt/HZO interface serves to decrease the leakage current.

Ferroelectric and Dielectric Properties of Hf0.5Zr0.5O2 Thin Film Near Morphotropic Phase Boundary

“…Finally, W/HZO/W capacitors with different electrode areas were passed through an annealing process in ambient N 2 under two different conditions, i.e., 500 C for 30 s (A1) and 700 C for 5 s (A2), to achieve different t-/o-phase ratios f t o according to the previous studies. [35,42] The elemental composition was evaluated through X-ray photoelectron spectroscopy (XPS). High-resolution transmission electron microscopy (HRTEM) and an X-ray reflectometer (XRR) were used to measure the film thickness.…”

Effect of Process Temperature on Density and Electrical Characteristics of Hf0.5Zr0.5O2 Thin Films Prepared by Plasma-Enhanced Atomic Layer Deposition

“…The thickness of the thin film was approximately 10 nm, and an o-phase crystalline structure was mainly observed. The disappearance of the o-phase structure near the interface is thought to be because of interface instability due to TiN diffusion [ 13 , 27 ]. Figure 3 b shows the EDS-based elemental composition profiles of the same thin film, and it can be observed that some of the Ti and N atoms diffused into the HZO thin film.…”

“…In this context, studies on improving the properties of HZO have been actively underway. In particular, research on the effects of crystal structure, oxygen defects inside thin films, grain size, and interface engineering using electrodes on changes in electrical properties has been mainly reported [ 10 , 11 , 12 , 13 , 14 ]. HZO thin films have a variety of crystalline phases such as tetragonal (t-, P4 2 /nmc), monoclinic (m-, P2 1 /c), and orthorhombic (o-, Pca2 1 ) phases, of which the o-phase exhibits ferroelectric properties.…”

Intrinsic ferroelectricity in Y-doped HfO2 thin films

“…The calculated ferroelectric polarization of the orthorhombic Pca21 phase of HfO2 is about 50.2 µC/cm 2 , which is consistent with the previous theoretical studies. [10][11][12][13][14] The polarization is directed along the c-axis, as enforced by the symmetry of the crystal, so that the a-and bcomponents of polarization are zero. The 5% Y doping slightly reduces the polarization down to about 49.9 µC/cm 2 , which indicates that Y does not play a decisive intrinsic role in high polarization values observed in our experiments, but rather helps to stabilize the orthorhombic Pca21 phase of hafnia.…”

“…The small crystal grain sizes lead to proliferation of structural defects (low crystallinity) in the form of grain boundaries, which are expected to undermine and obscure ferroelectric properties. 9 Indeed, it has been challenging to elucidate the crystal structure of the ferroelectric o-phase; to date, most of the experimentally observed spontaneous polarization values are significantly lower than the theoretically predicted ones (40-60 µC/cm 2 ) [10][11][12][13][14] .…”