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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]

Atomic layer engineering is investigated to tailor the morphotropic phase boundary (MPB) between antiferroelectric, ferroelectric, and paraelectric phases. By increasing the HfO2 seeding layer with only 2 monolayers, the overlying ZrO2 layer experiences the dramatic phase transition across the MPB. Conspicuous ferroelectric properties including record‐high remanent polarization (2Pr ≈ 60 µC cm−2), wake‐up‐free operation, and high compatibility with advanced semiconductor technology nodes, are achieved in the sub‐6 nm thin film. The prominent antiferroelectric to ferroelectric phase transformation is ascribed to the in‐plane tensile stress introduced into ZrO2 by the HfO2 seeding layer. Based on the high‐resolution and high‐contrast images of surface grains extracted precisely by helium ion microscopy, the evolution of the MPB between tetragonal, orthorhombic, and monoclinic phases with grain size is demonstrated for the first time. The result indicates that a decrease in the average grain size drives the crystallization from the tetragonal to polar orthorhombic phases. [ABSTRACT FROM AUTHOR]

In recent years, aluminum matrix composites (AMCs) have attracted attention due to their promising properties. However, the presence of ceramic particles in the aluminum matrix renders AMCs a high corrosion rate and makes it challenging to use traditional corrosion protection methods. In this study, atomic layer deposition (ALD) techniques were used to deposit HfO2, ZrO2, TiO2, and Al2O3 thin films on AMC reinforced with 20 vol.% SiC particles. Our results indicate that the presence of micro-cracks between the Al matrix and SiC particles leads to severe micro-crack-induced corrosion in Al-SiC composites. The ALD-deposited films effectively enhance the corrosion resistance of these composites by mitigating this micro-crack-induced corrosion. Among these four atomic-layer deposited films, the HfO2 film exhibits the most effective reduction in the corrosion current density of Al-SiC composites in a 1.5 wt% NaCl solution from 1.27 × 10−6 A/cm2 to 5.89 × 10−11 A/cm2. The electrochemical impedance spectroscopy (EIS) investigation shows that HfO2 deposited on Al-SiC composites has the largest Rp value of 2.0 × 1016. The HfO2 film on Al-SiC composites also exhibits effective inhibition of pitting corrosion, remaining at grade 10 even after 96 h of a salt spray test. [ABSTRACT FROM AUTHOR]

Characteristics of atomic layer deposition (ALD)-grown ZnO thin films on sapphire substrates with and without three-pulsed ozone (O3) as oxidant precursor and post-deposition thermal annealing (TA) are investigated. Deposition temperature and thickness of ZnO epilayers are 180 °C and 85 nm, respectively. Post-deposition thermal annealing is conducted at 300 °C in the ambience of oxygen (O2) for 1 h. With strong oxidizing agent O3 and post-deposition TA in growing ZnO, intrinsic strain and stress are reduced to 0.49% and 2.22 GPa, respectively, with extremely low background electron concentration (9.4 × 1015 cm−3). This is originated from a lower density of thermally activated defects in the analyses of thermal quenching of the integrated intensity of photoluminescence (PL) spectra. TA further facilitates recrystallization forming more defect-free grains and then reduces strain and stress state causing a remarkable decrease of electron concentration and melioration of surface roughness. [ABSTRACT FROM AUTHOR]

Analytical electron microscopy has revealed the structure of thin films of thermally evaporated Au on atomic layer deposition (ALD) TiO2 deposited on glass substrates. An 11 nm thick TiO2 film was deposited at 200 °C with 417 ALD cycles using tetrakisdimethylamido titanium and H2O precursors. The Au film comprised small particles with diameters of ∼15 nm or less grown by Volmer-Weber growth mechanism on the TiO2 layer. Transmission electron microscopy analysis of the ALD TiO2 layer showed that it was amorphous and had Ca atoms incorporated into the film probably from the lime glass substrate. The effect of Ca atoms included in the TiO2 layer on the growth of Au particles is discussed. [ABSTRACT FROM AUTHOR]

An approach was proposed to characterize nanoscale ultrathin films using surface enhanced Raman scattering (SERS). Raman spectroscopy of the TiO2 film as thin as ∼2 nm, which was prepared by atomic layer deposition, was obtained by depositing a nanostructured Au layer on the film surface. Red-shift in the extinction spectrum of the nanostructured Au layer was observed with increasing TiO2 film thickness, ascribed to the increase in effective refractive index of the substrate slab and coupled plasmon resonance. This SERS technique can be applied to investigate a variety of solid-state ultrathin films in nanosclae materials and devices in future studies. [ABSTRACT FROM AUTHOR]

Enhanced ferroelectric properties of nanoscale ZrO 2 thin films by an HfO 2 seed layer are demonstrated in metal-ferroelectric-semiconductor (Si) capacitors and transistors prepared with a low thermal budget of 400 °C. The seeding effect of the HfO 2 layer leads to the enhancement of crystallization into the orthorhombic phase and the increase of remnant polarization of the sub-10 nm ZrO 2 /HfO 2 bilayer structure. The ferroelectric field-effect transistor with the ZrO 2 /HfO 2 bilayer gate stack reveals a large memory window of ~1.2 V and a steep subthreshold swing below 60 mV/decade. As compared with the Hf 0.5 Zr 0.5 O 2 thin film, superior ferroelectric properties of the ZrO 2 /HfO 2 bilayer structure show great potential for ferroelectric memory devices fabricated on Si substrates. [ABSTRACT FROM AUTHOR]

In past few years, there was a great amount of research on ferroelectric Al-doped HfO 2 (HAO) thin films which suffer from the need of high annealing temperatures to achieve significant ferroelectricity. In this work, we realize pronounced remnant polarization 2 P r ~29μC/cm2 of HAO using rapid electron beam annealing (EBA) with a large area. The simulation of electron beam trajectories reveals that the effect of EBA concentrates on the region ~20 nm below the sample surface, which highly benefits the process integration where a low thermal budget is required. The energy-dispersive X-ray and high-angle annular dark-field analyses reveal the interdiffusion between Al and Hf in the HAO layer treated by EBA. The pronounced ferroelectricity of HAO can be accounted for by the lattice strain, which facilities the formation of the orthorhombic phase, due to the substitution of Al for Hf as supported by the fast Fourier transformation diffraction pattern. [ABSTRACT FROM AUTHOR]

Low-temperature atomic layer deposition and high-temperature electron beam annealing (EBA) are used to achieve high-quality epitaxial AlN layers. Efficient energy transfer from the single exposure for only 1 min of electron irradiation with a large area contributes to substantial improvement in the film density and crystal quality of AlN thin films, as demonstrated by the X-ray reflectivity and the θ-2θ/ω-scan X-ray diffraction. High-resolution transmission electron microscopy indicates well-arranged lattice fringes in the epitaxial AlN layer on a sapphire substrate. A low surface roughness of the AlN epilayer, as revealed by the atomic force microscopy, suggests that the damage induced by the EBA treatment is insignificant. The outcomes indicate that the large-area rapid EBA is a low-damage and efficient technique for the recrystallization of thin films prepared at low temperatures. • AlN epilayers are prepared by atomic layer deposition and electron beam annealing. • Large-area electron beam annealing in a single exposure for a short treatment. • Electron irradiation leads to significant enhancement of crystal/physical properties. [ABSTRACT FROM AUTHOR]

Large stable ferroelectricity in nanoscale undoped zirconia (ZrO 2 ) thin films prepared without post-annealing has been demonstrated for the first time. Remanent polarizations up to 12 μC cm −2 were obtained in the as-deposited ZrO 2 thin films prepared by remote plasma atomic layer deposition at 300 °C substrate temperature on the Pt electrode. Ferroelectric crystallization of the films was achieved without post-annealing, which is highly beneficial to the application of the films in non-volatile memories and ultralow-power nanoelectronics. The existence of the ferroelectric orthorhombic phase with noncentrosymmetric space group Pbc 2 1 in the as-deposited ZrO 2 thin films was confirmed by high-resolution transmission electron microscopy. [ABSTRACT FROM AUTHOR]

The sub-5 nm Hf 0.5 Zr 0.5 O 2 (HZO) thin films have been studied for years; however, they still suffer from challenges including poor ferroelectricity, wake-up effect, and the need for high-temperature annealing. In this paper, the concept and the method of "monolayer engineering" by atomic layer deposition (ALD) are proposed and implemented, which leads to dramatic improvements in the crystallinity and ferroelectricity of the HZO thin film with a thickness of only ∼4 nm at a low annealing temperature of only 370 °C. By substituting one ZrO 2 for one HfO 2 atomic layer, a high ferroelectric remnant polarization (P r) ∼15 μC/cm2 is achieved in the HZO thin film. Moreover, the pronounced ferroelectric characteristics are demonstrated in the pristine state, indicating the nearly wake-up-free property of the HZO layer. This study manifests that the monolayer engineering by ALD enables atomic tailoring to enhance the material and physical properties of nanoscale thin films. [Display omitted] [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]

• Large-area, low-damage, and rapid electron beam annealing (EBA) technique. • Electron irradiation in a single exposure without the need of beam scanning. • Significant enhancement of the crystal quality of nanoscale GaN thin films by EBA. • Very clear lattice fringes in the HRTEM image reveals a high-quality GaN epilayer. • Low FWHM of X-ray rocking curve and low surface roughness of the 18 nm GaN layer. This paper reports significant enhancement of the crystalline quality of nanoscale GaN thin films by a large-area and rapid electron beam annealing (EBA) technique. A low full width at half maximum of only 185 arcsec of the X-ray rocking curve indicates a high-quality GaN epilayer, which is attributed to efficient energy transfer from the large-area electron irradiation into the film in a single exposure without the need of electron beam scanning. The high crystalline quality of the GaN epilayer was also evidenced by the very clear lattice fringes in the high-resolution transmission electron microscopy image. A smooth surface with a low surface roughness of the GaN layer also reveals low damage caused by the rapid EBA treatment. The promising results demonstrate that the low-damage, large-area, and rapid EBA is an effective technique for numerous applications that require an efficient annealing process with a low thermal budget. Large-area, low-damage, and rapid electron beam annealing for the efficient recrystallization of GaN thin films is demonstrated. [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]

Abstract: Long-term stable p-type ZnO films were grown by atomic layer deposition on semi-insulating GaAs substrates and followed by rapid thermal annealing (RTA) in oxygen ambient. Significant decrease in the electron concentration and increase in the hole concentration, together with the intensity enhancement of acceptor-related AoX spectral peak and the shift of bound exciton peak from DoX to AoX in the low-temperature photoluminescence spectra, were observed as the RTA temperature increased. Conversion of conductivity from intrinsic n-type to extrinsic p-type ZnO occurred at the RTA temperature of 600°C. The p-type ZnO film with a hole concentration as high as 3.44×1020 cm−3 and long-term stability up to 180days was obtained as the RTA treatment was carried out at 700°C. The results were attributed to the diffusion of arsenic atoms from GaAs into ZnO as well as the activation of As-related acceptors by the post-RTA treatment. [Copyright &y& Elsevier]

Abstract: Temperature-dependent photoluminescence (PL) from Si nanodots with Al2O3 surface passivation layers was studied. The Si nanodots were grown by low pressure chemical vapor deposition and the Al2O3 thin films were prepared by atomic layer deposition (ALD), respectively. The BOE (Buffer-Oxide-Etch) treatment resulted in the damaged surface of Si nanodots and thus caused dramatic reduction in the PL intensity. Significant enhancement of the PL intensity from Si nanodots after the deposition of Al2O3 thin films was observed over a wide temperature range, indicating the remarkable surface passivation effect to suppress the non-radiative recombination at the surface of Si nanodots. The results demonstrated that the Al2O3 surface passivation layers grown by ALD are effectually applicable to nanostructured silicon devices. [Copyright &y& Elsevier]

Abstract: This study demonstrated thin-film encapsulation of bulk-heterojunction polymer photovoltaic cells, utilizing a process based on atomic layer deposition (ALD) that both prevented degradation caused by ambient gases and served as an annealing step that increased the initial efficiency of the cells. With the ALD temperature set at 140°C and the total deposition time set at 1h, the photovoltaic cells, based on blended poly-3-hexylthiophene (P3HT) and [6,6]-phenyl C61 butyric acid methylester (PCBM), were optimally annealed during encapsulation, achieving a power conversion efficiency (PCE) of 3.66%. Encapsulating the cells with a 26nm Al2O3/HfO2 nanolaminated film overcoated with an epoxy resin protection layer enabled the cells to obtain an in-air degradation rate that was similar to cells that were stored in nominally O2/H2O-free atmosphere. The nanolaminated structure of the encapsulation film resolved the issue of hydrolysis-induced aging observed with Al2O3 films, owing to the hydrophobicity of the HfO2 layers. Additionally, extended exposure of the ALD precursors during the ALD process significantly improved the coverage of the ALD films over the P3HT/PCBM active layer at the perimeter of the cells. [Copyright &y& Elsevier]

[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]

An ~6.5 nm pure ZrO 2 thin film with a giant ferroelectric remanent polarization (P r) of ~50 μ Ccm − 2 and an effective piezoelectric coefficient (d 33) of 7−9 pm/V is reported. The film was prepared on a (111)-oriented Pt electrode using plasma-enhanced atomic layer deposition at 300 °C, followed by annealing at 400 °C, and exhibited a preferred orientation of the orthorhombic (111) planes in the in-plane direction. The P r value of ~50 μ Ccm − 2 is the largest reported to date for both perovskite and fluorite nanoscale ferroelectric thin films (< 120 nm) on a Pt electrode. Furthermore, the processing temperature of 300−400 °C is the lowest reported to date to produce a P r of ~50 μ Ccm − 2 in nanoscale ferroelectrics on a Pt electrode. The giant P r , ascribed to the preferred crystal orientation, was confirmed by the positive-up negative-down (PUND) polarization measurement with a long delay time to allow the relaxation of polarization. The effective d 33 was obtained using piezoresponse force microscopy with an interferometric displacement sensor to minimize the frequency-dependent artifacts and the effects of cantilever dynamics. The low-temperature preparation of the textured ZrO 2 ultrathin film with a giant P r is extremely advantageous for device scaling and process integration in advanced nanoelectronics. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Based on the engineering of the TiN capping layer, the tailoring of the crystalline phases and the paraelectric(PE)/antiferroelectric(AFE)/ferroelectric(FE) properties of nanoscale ZrO 2 thin films are demonstrated without any post-annealing treatment. The capping by the TiN layer leads to the conversion of ZrO 2 from the PE to the AFE electrical characteristics, while the removal of the TiN capping layer results in the AFE-to-FE phase transformation of ZrO 2. The nano-beam electron diffraction, high-resolution transmission electron microscopy and X-ray diffraction characterizations identify the presence of the AFE tetragonal and FE orthorhombic phases in ZrO 2 , and the observations reveal the emergence of the out-of-plane compressive and in-plane tensile strains in the ZrO 2 layers by the TiN capping layer as well. The results demonstrate the significant impact of the TiN capping layer effect on the crystalline phases and dielectric properties of nanoscale thin films at a low temperature, which may play an important role in the FE/AFE applications which need a low thermal budget. Unlabelled Image • The TiN capping layer induces ZrO 2 transformation from paraelectric amorphous phase to antiferroelectric tetragonal phase. • Etching TiN away results in relaxation of ZrO 2 from antiferroelectric tetragonal phase to ferroelectric orthorhombic phase. • The TiN layer can modulate the antiferroelectric and ferroelectric phases in ZrO 2 thin films without high-temperature annealing. [ABSTRACT FROM AUTHOR]

• The heating depth of atomic layer annealing (ALA) is less than 5 atomic layers. • The ALA-treated AlN layer is a high-quality epilayer with a low FWHM ~150 arcsec. • The film density of AlN is increased by ~11% by the ALA technique. • The dielectric constant of AlN is increased by ~35% by the ALA technique. • The leakage current is reduced by ~2 orders of magnitude by the ALA technique. • The threading dislocation density is suppressed by one order of magnitude by ALA. Conventional annealing techniques face tremendous challenges in nanoscale fabrication. For example, the heating depth of conventional annealing techniques is much greater than the critical dimension of nanoscale devices, resulting in excessive thermal budget and so degradation of device performance. In this study, the atomic layer annealing (ALA) technique of a sub-nanometer heating depth is demonstrated. ALA is an in-situ plasma treatment applied in the process of atomic layer deposition (ALD), resulting in delivery of energy to the surface of as-deposited thin films from the plasma. The ALA treatment introduced into each ALD cycle leads to significant enhancement of crystallinity, film density, and dielectric constant, as well as considerable suppression of leakage current and threading dislocation densities, of the AlN layer. These improvements of the AlN properties was degraded significantly with an increase of the cycle spacing of the ALA treatment in the ALD process, indicating the heating depth of the ALA technique is below 5 atomic layers. The result indicates that the ALA process of precise sub-nanometer heating depth plays a critical role to achieve high-quality nanoscale materials and devices. [ABSTRACT FROM AUTHOR]