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In this study, platinum (Pt) and tungsten (W), two materials with dissimilar coefficients of thermal expansion (CTE) and work functions (WF), are used as the top electrode (TE) and the bottom electrode (BE) in metal/ferroelectric/metal (MFM) structures to explore the ferroelectricity of hafnium zirconium oxide (HZO) with a thickness less than 10 nm. The electrical measurements indicate that a higher CTE mismatch between HZO and TE/BE is beneficial for enhancing the ferroelectric properties of nanoscale HZO thin films. The different WFs of TE and BE generate a built-in electric field in the HZO layer, leading to shifts in the hysteresis loops and the capacitance–voltage characteristics. The structural characterizations reveal that the preferred formation of the orthorhombic phase in HZO is dominated by the W BE. The device in which W is used as the TE and BE (the W/HZO/W MFM structure) presents the optimal ferroelectric performance of a high remanent polarization (2 P r = 55.2 μ C cm−2). The presence of tungsten oxide (WO x ) at the W/HZO interfaces, as revealed by high-resolution transmission microscopy, is also responsible for the enhancement of ferroelectric properties. This study demonstrates the significant effects of different CTEs and WFs of TE and BE on the properties of ferroelectric HZO thin films. [ABSTRACT FROM AUTHOR]

In the recent decade, there is a growing interest in Hf 0.5 Zr 0.5 O 2 (HZO) thin films owing to their well-behaved ferroelectricity and high compatibility with semiconductor integrated circuit technology. The ferroelectric properties of HZO are highly pertinent to the wake-up effect, which has been reported to be associated with the monoclinic (m-), orthorhombic (o-), and tetragonal (t-) phases. However, it is very challenging to distinguish the o- and t- phases by conventional X-ray diffraction. In this study, the HZO thin films with and without the need for the wake-up process to enhance the ferroelectricity were prepared, and the precession electron diffraction (PED) phase mapping technique was utilized to identify the crystalline phases in the HZO layers. The PED characterization reveals the correlation between the phase transformation and the wake-up effect in HZO. The absence of the t-phase is responsible for the wake-up-free property in the ferroelectric HZO thin film. The wake-up-free and pronounced ferroelectricity of the nanoscale HZO thin film in this study may bring a practical impact on a variety of ferroelectric applications. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Ferroelectric (FE) Hf 0.5 Zr 0.5 O 2 (HZO) is treated with atomic layer annealing (ALA). • The ALA process upon HfO 2 monolayer induces superior crystalline and FE properties. • Insignificant wake-up effect is achieved in HZO thin films without post annealing. In recent years, ferroelectric hafnium zirconium oxide (Hf 0.5 Zr 0.5 O 2 , HZO) has emerged as a promising candidate for nonvolatile memory and energy storage devices. A low thermal budget technique for achieving sub-10 nm HZO thin films with pronounced ferroelectricity is highly demanded for ferroelectric applications such as advanced semiconductor technology nodes. In this paper, the atomic layer annealing (ALA) technique, which is the in situ He/Ar plasma treatment incorporated into the atomic layer deposition cycle, is demonstrated to achieve the transformation from amorphous to orthorhombic phase in sub-10 nm HZO layers without the need of any high-temperature post annealing. As compared with the ALA process conducted on each ZrO 2 monolayer, the ALA treatment performed on each HfO 2 monolayer is much preferred in terms of superior crystallinity and ferroelectric properties of the HZO thin films. Hence a high remanent polarization together with a nearly wake-up-free property are accomplished in the HZO layer. The study demonstrates ALA is an effective technique to realize the atomic tailoring of crystalline quality and ferroelectric/dielectric characteristics of nanoscale thin films at a low temperature, which is very favorable in a variety of applications including biomedical, wearable, and nanoelectronic devices, in which a low thermal budget process is required. [ABSTRACT FROM AUTHOR]

[Display omitted] • The FE phase can be induced with ALD TiN capping under low thermal budget (∼300 °C). • The record remnant polarization in 6nm HZO thin films is achieved in this work. • The TiO x N y emerges between HZO and ALD TiN can lead to notable confinement effect. Ferroelectric Hf 0.5 Zr 0.5 O 2 (HZO) thin films has attracted a large amount of interests in academia and industry. The scaling of the HZO thickness down to the sub-10 nm region with a low thermal budget is essential in practical applications. However, pronounced ferroelectricity in sub-10 nm HZO thin films prepared at a low process temperature is rarely reported. In this paper, significant ferroelectricity is reported in 6 nm HZO thin films by the TiN capping electrode prepared by atomic layer deposition (ALD). Capping the ALD TiN layer leads to the crystallization of an as-deposited amorphous HZO thin film to the ferroelectric orthorhombic phase. The post-annealing treatment at a low temperature of 400 °C contributes to a record remnant polarization (2 P r) of ∼ 51.2 μC/cm2 in sub-10 nm HZO. The mechanisms of the TiN capping effect are investigated based on the TiN capping layers prepared by ALD and sputtering. The distinct ferroelectric properties can be attributed to the formation of a large in-plane tensile stress and the TiO x N y mixed phase by the ALD TiN capping layer. The realization of the low thermal budget and high 2 P r in sub-10 nm HZO thin films by the ALD TiN capping layer is highly promising for next-generation ferroelectric applications. [ABSTRACT FROM AUTHOR]