UV-enhanced atomic layer deposition of ZrO2 thin films at room temperature

A UV-enhanced atomic layer deposition (UV-ALD) process was developed to deposit ZrO₂ thin films on poly(ethylene terephthalate) (PET) polymer substrates using zirconium tetra-tert-butoxide (ZTB) and H₂O as precursors with UV light. In the UV-ALD process, the surface reactions were found to be self-limiting and complementary enough to yield uniform, conformal, and pure ZrO₂ thin films on polymer substrates at room temperature. The UV light was very effective to obtain the high-quality ZrO₂ thin films with good adhesive strength on polymer substrates. The ZrO₂ thin films exhibit large-scale uniformity, sharp interfaces, and unique electrical properties.     

Thermal treatment effect on the optical properties of ZrO2 thin films deposited by thermionic vacuum arc

This paper shows the ex situ thermal treatment effects of the ZrO₂ thin films obtained by TVA (thermionic vacuum arc) technique on the optical properties (e.g., transmittance, refractive index and band-gap energy) of ZrO₂ thin films. The crystal structure, surface and optical properties were investigated for ZrO₂ thin films deposited on glass substrates by thermionic vacuum arc (TVA) method. The thermal treatment effect on the optical properties of the thin films was determined. The XRD analysis showed that the deposited ZrO₂ thin films have baddeleyite (monoclinic) and zirconium (hexagonal) structures. The thicknesses and refractive index were determined by interferometric measurements. The thin films were thermal treated at different temperatures (350 °C, 450 °C and 550 °C), and the analysis showed that the optical properties of ZrO₂ deposited thin films were improved by thermal treatment at 450 °C.     

Interfacial layer growth of ZrO2 films on silicon

In this work, the interfacial layer growth for both as-deposited and annealed ZrO₂ thin films on silicon is analyzed in detail by the high-resolution cross-sectional transmission electron microscope and spectroscopic ellipsometry. For as-deposited ZrO₂/SiO₂/Si, the thickness of a SiO₂-like layer at the silicon interface was found to depend on the oxygen partial pressure during deposition. At oxygen partial pressure ratio of above 50% the interfacial silicon oxide thickness increased through oxygen diffusion through the ZrO₂ film and silicon consumption at the interface. At oxygen partial pressure ratio in the range 7-50%, the visible growth of interfacial silicon oxide layer was not present. The interfacial layer for ZrO₂/Si with optimal partial pressure (15%) during annealing at 600 °C was found to be the two-layer structure composed of the ZrSi_xO_y overlayer and the SiO_x downlayer. The formation of the interfacial layer is well accounted for diffusion mechanisms involving Si indiffusion and grain-boundary diffusion.     

Characterization of sol-gel derived TiO2/ZrO2 films and powders by Raman spectroscopy

The effect of zirconium dioxide addition on crystal structure of sol-gel TiO₂ mesoporous films and powders has been investigated by means of Raman spectroscopy, X-Ray diffraction, and Atomic force microscopy. Zirconium incorporation (up to 30 mol%) into TiO₂ lattice resulted in the formation of Ti_1 − xZr_xO₂ solid solution with anatase structure for the binary powders has been proved. Appearance of tetragonal ZrO₂ phase was observed for the samples with high zirconium content.     

Evaluation of ion conductivity of ZrO2 thin films prepared by reactive sputtering in O2, H2O, and H2O + H2O2 mixed gas

Hydrated ZrO₂ thin films were prepared by reactive sputtering in O₂, H₂O, and H₂O + H₂O₂ mixed gas, and the effect of the sputtering atmosphere on ion conductivity of the films was investigated. The results showed that the films deposited in O₂ gas exhibited poor ion conductivity; however, the ion conductivities of the films deposited in the other two kinds of atmosphere were similar and 300-500 times higher than that of the films deposited in O₂ gas. It was indicated that the higher ion conductivity of the films was caused by lower film density and higher water content.     

Chemical deposition of Al2O3 thin films on Si substrates

Uniform Al₂O₃ films were deposited on silicon substrates by the sol–gel process from stable coating solutions. The technological procedure includes spin coating deposition and investigating the influence of the annealing temperature on the dielectric properties. The layers were studied by Fourier transform infrared spectroscopy and Scanning Electron Spectroscopy. The electrical measurements have been carried out on metal–insulator–semiconductor (MIS) structures. The C–V curves show a negative fixed charge at the interface and density of the interface state, Dit, 3.7 × 10¹¹ eV^− 1cm^− 2 for annealing temperature at 750 °C.     

A study of textured non-stoichiometric MoTe2 thin films used as substrates for textured stoichiometric MoS2 thin films

Textured MoTe₂ films have been prepared by sequential evaporation of the constituents followed by annealing under a tellurium pressure. The films are systematically textured with the c-axis of the crystallites perpendicular to the plane of substrate, however, the film composition is difficult to control and even after process optimization the films are tellurium deficient. This is thought to be caused by the electro negativity difference of the constituents.The textured MoTe₂ films have been used as substrates on which to grow MoS₂ films by annealing under a pressure of sulfur that allows textured MoS₂ films to be grown with good crystalline properties. The presence of sulfur at the surface and annealing under dynamic vacuum is important for this process and moreover, suppresses the superficial oxidation of the Mo and Te constituents.     

Structure and mechanical properties of ZrO2 films deposited by gas flow sputtering

ZrO₂ films were deposited by reactive gas flow sputtering (GFS) where voltage is applied to a cyindrical hollow-cathode target from a DC source, the discharge being produced at relatively high sputtering pressure. In this system, secondary electrons form a major component of the total current flow and lead to heating of the substrate which in turn has an effect on the properties of deposited films. The present experiments were carried out under the following conditions: Ar gas flow rate of 200 sccm, O₂ flow rate FO₂ in the range between 0.003 and 1 sccm, and sputtering power (P_S) in the range of 50-800 W. The reults showed that the crystal structure of the films deposited for P_S below 200 W was monoclinic but for P_S above 400 W, the films included tetragonal cystals of stable structure formed at high temperature by the electron bombardment. The films were formed with grains of 20-100 nm in diameter in a porous structure. The mechanical properties of the films were determined by a nanoindentation technique. Martens hardness (H_M) of the porous films was found to be in the range between 220 and 330 MPa which is substantially less than that of films typically deposited by rf magnetron sputtering.     

Structure and property changes of ZrO2/Al2O3/ZrO2 laminate induced by low-temperature NH3 annealing applicable to metal-insulator-metal capacitor

Phase transformation and morphology evolution of ZrO₂/Al₂O₃/ZrO₂ laminate induced by the post-deposition NH₃ annealing at 480 °C were studied and the effect on the electrical property of the TiN/ZrO₂/Al₂O₃/ZrO₂/TiN capacitor module was evaluated in dynamic random access memory cell. Experimental results indicated N could indeed be incorporated into the dielectric laminate by the low-temperature NH₃ annealing, resulting in tetragonal-to-cubic phase transformation and small crystallites in the ZrO₂ layers. The C residue and Cl impurity in the ZrO₂/Al₂O₃/ZrO₂ laminate, which derived from the dielectric film formation and capping TiN layer deposition, respectively, could also be reduced by the nitridation process. As a result of the better surface morphology and less impurity content, lower dielectric leakage current and longer reliability lifetime were observed for the nitrided ZrO₂/Al₂O₃/ZrO₂ capacitor. This study demonstrates the low-temperature NH₃ annealing on ZrO₂/Al₂O₃/ZrO₂ dielectric can be applicable to the metal-insulator-metal capacitor structure with nitride-based electrode, which brings advantages over mass production-wise property improvements and extends the practical applicability of the ZrO₂/Al₂O₃/ZrO₂ dielectric.     

Synthesis of GaN nanorods by ammoniating Ga2O3 films on In2O3 layer deposited on Si (111) substrates

GaN nanorods were synthesized by ammoniating Ga₂O₃/In₂O₃ thin films deposited on Si (111) with magnetron sputtering. X-ray diffraction, Scanning electronic microscope and high-resolution TEM results show that they are GaN single crystals, the sizes of which vary from 2 to 7 μm in length and 200 to 300 nm in diameter. In₂O₃ middle layer plays an important role in the GaN nanorod growth.     

Growth of Cu2ZnSnS4 thin films on Si (100) substrates by multisource evaporation

Cu₂ZnSnS₄ films were grown on Si (100) by vacuum evaporation using elemental Cu, Sn, S and binary ZnS as sources. X-ray diffraction patterns of films grown at different substrate temperatures indicated that polycrystalline growth was suppressed and the orientational growths were relatively induced in a film grown at higher temperatures. Tetragonal structure of Cu₂ZnSnS₄ films was confirmed by studying RHEED patterns. The existence of c-axis ([001] direction) growth, two kinds of a-axis (〈100〉 direction) growth and four kinds of {112} twins which can be classified as two symmetrical pairs is proposed. Broad emissions at around 1.45 eV and 1.31 eV were observed in the photoluminescence spectrum measured at 13 K.     

UV Raman spectroscopic study on the surface phase of ZrO2 modified with Nd2O3

The Nd₂O₃ modified ZrO₂ was synthesized using two methods of co-precipitation (Nd-ZrO₂) and wet impregnation (Nd/ZrO₂). The surface and bulk crystalline phases of Nd₂O₃ modified ZrO₂ were investigated by using UV Raman spectroscopy, visible Raman spectroscopy, and X-ray diffraction (XRD). It is observed that the tetragonal phase in the surface region of Nd-ZrO₂ was not effectively stabilized by Nd₂O₃, as Nd₂O₃ is mainly present in the bulk of Nd-ZrO₂. However, in Nd/ZrO₂, it is found that with the impregnation of 0.5 mol% Nd₂O₃ on ZrO₂, the surface tetragonal phase of Nd/ZrO₂ can be stabilized even after calcination at 700 °C. The UV Raman results indicate that a disordered structure, or intermediate structure, which is involved in the transition from the tetragonal to the cubic phase, is formed at the surface region of Nd/ZrO₂. The formation of the aforementioned intermediate structure inhibits the phase transition from tetragonal to monoclinic in the surface region of Nd/ZrO₂. Furthermore, it is observed that the mixed tetragonal and monoclinic phases in the surface region of ZrO₂ which has been impregnated with Nd₂O₃ can also be stabilized after calcination at 700 °C. This work provides a simple method for controlling the surface phase of ZrO₂ at high temperatures.     

Efficient two-color luminescence of Er/Yb/Li:ZrO2 nanocrystals

We demonstrate the upconversion-photoluminescence spectra of Er³⁺, Yb³⁺ and Li⁺ ions doped ZrO₂ nanocrystals. By introducing Li⁺, emission intensities of single green and single red band increase by a factor of 1.93 and 1.65, respectively. Powder X-ray diffraction data and decreased slopes of the excitation power dependences on upconverted emission intensities give evidences that Li⁺ ions can tailor the local structure of host lattice and improve energy transfer processes from Yb³⁺ to Er³⁺, respectively.     

Surface analysis of β-FeSi2 layer epitaxially grown on Si(100)

The epitaxial growth process of β-FeSi₂ on Si(100) surface under ultrahigh vacuum condition has been studied by low energy electron diffraction (LEED) and low energy ion scattering spectroscopy (LEIS). The LEED pattern of Si (100)-2×1 changes into amorphous structure with Fe deposition of about 10 Å at room temperature. With annealing at 540 °C, the LEED pattern shows 2×2 structure corresponding to the formation of the epitaxial β-FeSi₂ (100) template layer. The α-scan in Li⁺-LEIS and X-ray diffraction (XRD) study strongly suggest that the topmost surface of the 2×2 structure is terminated by Si atoms. By XRD, it is shown that the β-FeSi₂ develops with characteristic orientation even if iron reactant is deposited onto the template surface.     

Electrical characteristics of a ZrO2/SiO2 modified tunnel barrier for low-temperature non-volatile memory

The electrical characteristics of nonvolatile memory, which consists of an asymmetrical ZrO₂/SiO₂ (ZO) modified tunnel barrier, a high-k HfO₂ trapping layer and an Al₂O₃ blocking layer, were investigated for the application of a tunnel barrier engineered nonvolatile memory at low process temperatures. The efficiency of the ZO modified tunnel barrier on the charge trap flash (CTF) memory cell was compared to a conventional single SiO₂ tunnel barrier. The ZO tunnel barrier revealed field sensitivity larger than the single SiO₂ tunnel barrier. The programming and erasing speeds as well as the retention and endurance characteristics of CTF memory were largely enhanced. Moreover, the forming gas annealing process in 2% diluted H₂/N₂ ambient improved the charging trapping property and tunneling sensitivity of the ZO modified tunnel barrier.     

Annealing effects on the structural properties of IrO2 thin films

We have demonstrated the structural and morphological changes of iridium oxide (IrO₂) films by the thermal annealing process. We have characterized the samples by using the X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX). The Ir-related XRD peaks predominantly appeared after the thermal annealing at 750-1000 °C. SEM images revealed that the films became quite uneven in thickness by annealing at 750 °C, whereas island-like structures were found to agglomerate on substrate surfaces by annealing at 1000 °C. From EDX and XRD analysis, we suggested that the agglomerated structures mainly consisted of Ir phase.     

Growth of Cu2ZnSnS4 thin films using sulfurization of stacked metallic films

We fabricated Cu₂ZnSnS₄ (CZTS) thin films through sulfurization of stacked metallic films. Three types of Cu-Zn-Sn metallic films, i.e., Cu-rich, Cu-correct and Cu-poor precursor films were sputtered onto Mo-coated glass. The sulfurization of stacked Cu-Zn-Sn alloy films was performed at a relatively high temperature, 570 °C, with S-powder evaporation. CZTS films from Cu-rich and Cu-correct precursors showed a Cu_2 − xS phase on the film surface, while CZTS films from Cu-poor precursors didn't show the Cu_2 − xS phase. However, all films didn't exhibit any extra secondary phase and exhibited good crystalline textures even with Cu-ratio differences in metallic precursor films. Fabricated CZTS films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and Raman scattering measurements. SEM cross-section images of CZTS films showed that Cu-poor CZTS films were grown with more smooth film surface compared with other types of CZTS films.     

Single-step sputtered Cu2SnSe3 films using the targets composed of Cu2Se and SnSe2

Cu₂SnSe₃ thin films were prepared by single-step D.C. sputtering at 100-400 °C for 3 h using targets composed of Cu₂Se and SnSe₂ in three different ratios of 2/1 (target A), 1.8/1 (target B), and 1.6/1 (target C). The advantages of self-synthesized SnSe₂ instead of commercially available SnSe for depositing Cu₂SnSe₃ thin films were demonstrated. Effects of target composition and substrate temperature on the properties of Cu₂SnSe₃ thin films were investigated. Structure, surface morphology, composition, electrical and optical properties at different process conditions were measured. The 400 °C-sputtered films obtained from target B display with direct band gap of 0.76 eV, electrical resistivity of 0.12 Ω cm, absorption coefficient of 10⁴-10⁵ cm^− 1, carrier concentration of ∼ 1.8 × 10¹⁹ cm^− 3, and electrical mobility of 2.9 cm²/V s.     

Etching characteristics of Al2O3 thin films in inductively coupled BCl3/Ar plasma

The investigation of Al₂O₃ etch characteristics in the BCl₃/Ar inductively coupled plasma was carried out in terms of effects of input process parameters (gas pressure, input power, bias power) on etch rate and etch selectivity over poly-Si and photoresist. It was found that, with the changes in gas pressure and input power, the Al₂O₃ etch rate follows the behavior of ion current density while the process rate is noticeably contributed by the chemical etch pathway. The influence of input power on the etch threshold may be connected with the concurrence of chemical and physical etch pathways in ion-assisted chemical reaction.     

Red light from ZrO2:Eu nanostructures

Zirconia nanocrystals doped with europium ions were developed envisaging optical applications. The nanostructures were produced using zirconyl nitrate (ZrO(NO₃)₂·H₂O) and europium nitrate (Eu(NO₃)₃·5H₂O) as cation precursors, and urea (C₂H₅NO₂) as the fuel, by the combustion synthesis process. The lanthanide-doped nanostructures were characterized by X-ray diffraction, transmission electron microscopy, Raman spectroscopy and photoluminescence. X-ray diffraction revealed the presence of tetragonal and monoclinic crystalline ZrO₂ phases. The latter was found to be a minority phase as identified by Raman and corroborated by the observed europium luminescence when compared to the intraionic emission in crystalline tetragonal fibres grown by the laser floating zone technique. Bright red europium luminescence is observed at room temperature when the combustion synthesized zirconia powders are excited with ultraviolet radiation. The spectroscopic properties of the europium ions in the powders are ascertained by comparing combined excitation–emission measurements with those from crystalline fibres.