Low-Temperature Deposition of Zirconium Oxide-Based Nanocrystalline Films by Alternate Supply of Zr[OC(CH3)3]4 and H2O

Contribution of micropores in porous zirconia spheres to high optical transparency of dental resin composites

Transparency to UV-Vis light and radiopacity of dental resin composites containing zirconia (ZrO2) fillers were investigated. The transparency of the resin composite containing porous ZrO2 spheres was much higher than that containing irregularly shaped ZrO2 particles. Calcination of the porous ZrO2 spheres at high temperatures led to dramatically reduced specific surface areas and pore volumes. The transparency of the resin composite containing the calcined porous ZrO2 spheres drastically decreased as the calcination temperature increased. Then, the enhanced UV-Vis transmittance of the resin composite containing porous ZrO2 spheres is attributed to the concentration and physical characteristics of the pores. The radiopacity of the resin composites containing porous ZrO2 spheres increased slightly with increasing calcination temperature. This study revealed that the internal structure of the ZrO2 fillers mainly influenced in the UV-Vis light transmittance of the resin composites.

Amidoxime-Containing Zr and Hf Atomic Layer Deposition Precursors for Metal Oxide Thin Films

In this article, we discuss the synthesis of eight novel zirconium and hafnium complexes containing amidoxime ligands as potential precursors for atomic layer deposition (ALD). Two amidoximes, viz., (E)-N'-hydroxy-N,N-dimethylacetimidamide (mdaoH) and (Z)-N'-hydroxy-N,N-dimethylpivalimidamide (tdaoH), along with their Zr and Hf homoleptic complexes, Zr(mdao)4 (1), Hf(mdao)4 (2), Zr(tdao)4 (3), and Hf(tdao)4 (4) were prepared. We further synthesized heteroleptic compounds with different physical properties by introducing cyclopentadienyl (Cp) ligand, namely, CpZr(mdao)3 (5), CpHf(mdao)3 (6), CpZr(tdao)3 (7), and CpHf(tdao)3 (8). Thermogravimetric analysis was used for the assessment of the evaporation characteristics of complexes 1, 2, 5, and 6, and it revealed multistep weight losses with high residues. On the other hand, the thermogravimetric analysis curves of complexes 3, 4, 7, and 8 comprising tdao ligands revealed single-step weight losses with moderate residues. Single-crystal X-ray diffraction studies of complexes 1, 3, and 7 showed that all of the complexes have monomeric molecular structures. Complex 7 exhibited a low melting point (75 °C), good volatility, and high thermal stability compared with other complexes. Therefore, an atomic layer deposition process for the growth of ZrO2 was developed by using ZrCp(tdao)3 (7) as a novel precursor.

Thin-Film Engineering of Mechanical Fragmentation Properties of Atomic-Layer-Deposited Metal Oxides

Mechanical fracture properties were studied for the common atomic-layer-deposited Al₂O₃, ZnO, TiO₂, ZrO₂, and Y₂O₃ thin films, and selected multilayer combinations via uniaxial tensile testing and Weibull statistics. The crack onset strains and interfacial shear strains were studied, and for crack onset strain, TiO₂/Al₂O₃ and ZrO₂/Al₂O₃ bilayer films exhibited the highest values. The films adhered well to the polyimide carrier substrates, as delamination of the films was not observed. For Al₂O₃ films, higher deposition temperatures resulted in higher crack onset strain and cohesive strain values, which was explained by the temperature dependence of the residual strain. Doping Y₂O₃ with Al or nanolaminating it with Al₂O₃ enabled control over the crystal size of Y₂O₃, and provided us with means for improving the mechanical properties of the Y₂O₃ films. Tensile fracture toughness and fracture energy are reported for Al₂O₃ films grown at 135 °C, 155 °C, and 220 °C. We present thin-film engineering via multilayering and residual-strain control in order to tailor the mechanical properties of thin-film systems for applications requiring mechanical stretchability and flexibility.

Structure and Dielectric Property of High-k ZrO2 Films Grown by Atomic Layer Deposition Using Tetrakis(Dimethylamido)Zirconium and Ozone

High-k metal oxide films are vital for the future development of microelectronics technology. In this work, ZrO₂ films were grown on silicon by atomic layer deposition (ALD) using tetrakis(dimethylamido)zirconium and ozone as precursors. The relatively constant deposition rate of 0.125 nm/cycle is obtained within the ALD temperature window of 200-250 °C. The film thickness can be precisely controlled by regulating the number of ALD cycle. The ZrO₂ films formed at 200-250 °C have an O/Zr atomic ratio of 1.85-1.9 and a low content of carbon impurity. ZrO₂ film begins to crystallize in ALD process above 210 °C, and the crystal structure is changed from cubic and orthorhombic phases to monoclinic and orthorhombic phases with increasing the deposition temperature to 350 °C. Moreover, the effect of annealing temperature on dielectric properties of ZrO₂ film was studied utilizing ZrO₂-based MIS device. The growth of the interface layer between ZrO₂ and Si substrate leads to the decrease in the capacitance and the leakage current of dielectric layer in the MIS device after 1000 °C annealing. ZrO₂ film exhibits the relatively high dielectric constant of 32.57 at 100 kHz and the low leakage current density of 3.3 × 10^-6 A cm^-2 at 1 MV/cm.

Effects of Ar Addition to O2 Plasma on Plasma-Enhanced Atomic Layer Deposition of Oxide Thin Films

A method for significantly increasing the growth rates (GRs) of high- k oxide thin films grown via plasma-enhanced atomic layer deposition (PE-ALD) by enhancing the plasma density through the addition of Ar gas to the O₂ plasma oxidant was developed. This approach led to improvements of ∼60% in the saturation GRs of PE-ALD ZrO₂, HfO₂, and SiO₂. Furthermore, despite the significantly higher GR enabled by PE-ALD, the mechanical and dielectric properties of the PE-ALD oxide films were similar or even superior to those of films grown via the conventional O₂ plasma process. Optical emission spectroscopy analyses in conjunction with theoretical calculation of the electron energy distribution function revealed that adding Ar gas to the O₂ plasma increased the density of high-energy electrons, thereby generating more O₂ plasma species, such as ions and radicals, which played a key role in improving the GRs and the properties of the films. This promising approach is expected to facilitate the high-volume manufacturing of films via PE-ALD, especially for use as gate insulators in thin-film transistor-based devices in the display industry.

Zirconium Modification Promotes Catalytic Activity of a Single-Site Cobalt Heterogeneous Catalyst for Propane Dehydrogenation

The effect of Zr modification on the catalytic activity of Co/SiO₂ was investigated for nonoxidative propane dehydrogenation. Isolated Zr on SiO₂ surface sites were prepared by organometallic synthesis using Zr(O ^t Bu)₄ as a precursor. The resulting Zr/SiO₂ support was functionalized with Co²⁺ ions via strong electrostatic adsorption. Spectroscopic (diffuse reflectance infrared Fourier transform spectroscopy, UV-vis, electron paramagnetic resonance) and microscopic characterization (transmission electron microscopy, scanning transition electron microscopy) results are consistent with single-site cobalt that preferentially associates with the mono-dispersed Zr at a variety of loadings and Co/Zr ratios. The oxidation state of Co in the as-prepared Co/SiO₂ and Co-Zr/SiO₂ was both +2 with tetrahedral and octahedral geometries, respectively. In situ X-ray absorption near edge structure and extended X-ray absorption fine structure results confirmed that the oxidation state of Co remained as +2 under reaction condition for both Co/SiO₂ and Co-Zr/SiO₂ samples and both catalysts have tetrahedral Co²⁺ as the active catalyst. Despite similar Co coordination environments, the catalytic activity and selectivity was significantly improved by the Zr modification of the silica support versus Co/SiO₂. This was attributed to the change in oxygen donor ability and Co-O bond strength of the ≡SiO-Zr-O sites of Co-Zr/SiO₂ compared with the ≡SiO- ligands in Co/SiO₂. These results show that tuning of the support SiO₂ oxygen donation ability by use of an anchoring site (e.g., ≡SiO-Zr-O^-) can be used to alter both rate and selectivity of propane dehydrogenation with single-site heterogeneous catalysts. These results also show some preference for Co²⁺ active sites to associate with ≡SiO-Zr-O^- sites over ≡SiO-.

Theoretical study on the initial reaction mechanisms of ansa-metallocene zirconium precursor on hydroxylated Si(1 0 0) surface

The initial reaction mechanisms for depositing ZrO2 thin films using ansa-metallocene zirconium (Cp2CMe2)ZrMe2 precursor were studied by density functional theory (DFT) calculations. The (Cp2CMe2)ZrMe2 precursor could be absorbed on the hydroxylated Si(1 0 0) surface via physisorption. Possible reaction pathways of (Cp2CMe2)ZrMe2 were proposed. For each reaction, the activation energies and reaction energies were compared, and stationary points along the reaction pathways were shown. In addition, the influence of dispersion effects on the reactions was evaluated by non-local dispersion corrected DFT calculations.

Atomic-Layer Deposition of ZrO2 Thin Films Using New Alkoxide Precursors

Atomic layer deposition is a promising technique for the deposition of ZrO2 thin films for high-k gate dielectric applications. However, there are a number of problems associated with existing Zr precursors such as ZrCl4 and [Zr(OBut)4]. In this paper, we examine the ALD of ZrO2 using the new alkoxide complexes, [Zr(OBut)2(dmae)2], [Zr(OPr1)2(dmae)2] and [Zr(dmae)4] (dmae = [OCH2CH2NMe2]), and compare the results with data obtained using [Zr(OBut)4].