Yttrium Oxide Films Research Articles

The influence of annealing on yttrium oxide thin film deposited by reactive magnetron sputtering: Process and microstructure

Yttrium oxide thin films were prepared by reactive magnetron sputtering in different deposition condition with various oxygen flow rates. The annealing influence on the yttrium oxide film microstructure is investigated. The oxygen flow shows a hysteresis behavior on the deposition rate. With a low oxygen flow rate, the so called metallic mode process with a high deposition rate (up to 1.4µm/h) was achieved, while with a high oxygen flow rate, the process was considered to be in the poisoned mode with an extremely low deposition rate (around 20nm/h). X-ray diffraction (XRD) results show that the yttrium oxide films that were produced in the metallic mode represent a mixture of different crystal structures including the metastable monoclinic phase and the stable cubic phase, while the poisoned mode products show a dominating monoclinic phase. The thin films prepared in metallic mode have relatively dense structures with less porosity. Annealing at 600 °C for 15h, as a structure stabilizing process, caused a phase transformation that changes the metastable monoclinic phase to stable cubic phase for both poisoned mode and metallic mode. The composition of yttrium oxide thin films changed from nonstoichiometric to stoichiometric together with a lattice parameter variation during annealing process. For the metallic mode deposition however, cracks were formed due to the thermal expansion coefficient difference between thin film and the substrate material which was not seen in poisoned mode deposition. The yttrium oxide thin films that deposited in different modes give various application options as a nuclear material.

Flame-Sprayed Y2O3 Films with Metal-EDTA Complex Using Various Cooling Agents

In this study, yttrium oxide (Y2O3) films were synthesized from a metal-ethylenediaminetetraacetic (metal-EDTA) complex by employing a H2-O2 combustion flame. A rotation apparatus and various cooling agents (compressed air, liquid nitrogen, and atomized purified water) were used during the synthesis to control the thermal history during film deposition. An EDTA·Y·H complex was prepared and used as the staring material for the synthesis of Y2O3 films with a flame-spraying apparatus. Although thermally extreme environments were employed during the synthesis, all of the obtained Y2O3 films showed only a few cracks and minor peeling in their microstructures. For instance, the Y2O3 film synthesized using the rotation apparatus with water atomization units exhibited a porosity of 22.8%. The maximum film’s temperature after deposition was 453 °C owing to the high heat of evaporation of water. Cooling effects of substrate by various cooling units for solidification was dominated to heat of vaporization, not to unit’s temperatures.

Temperature induced upconversion behaviour of Ho3+-Yb3+ codoped yttrium oxide films prepared by pulsed laser deposition

Pulsed laser deposited Ho3+-Yb3+ codoped yttrium oxide films were grown on silicon substrates in vacuum at different substrate temperatures (373, 573, 773 and 973 K). The deposited films have shown a phase transition on increasing the substrate temperature, as confirmed by the X-ray diffraction analysis. The grain distribution and surface roughness of the deposited thin films have been estimated by atomic force microscopy measurements. In the optical properties study upconversion luminescence at 547, 656 and 758 nm was revealed upon 980 nm excitation. 773 K was found to be the best substrate temperature owing to the thickest deposited layer, as indicated by Auger depth profile analysis of the prepared films. A non-tunable bright green upconversion emission due to the involvement of a two photon process was established and a possible excitation-emission mechanism is explained by using an energy level diagram of the dopant ions.

Efficient upconversion in Er3+ doped Y2O3/Si thin film deposited by aerosol UV-assisted MOCVD process

Erbium doped yttrium oxide films (Er:Y2O3) upconversion layers were prepared by aerosol-UV assisted metal-organic chemical vapor deposition (MOCVD) at 410C and annealed at 800°C. The effect of erbium concentration on their structure and optical properties were investigated using scanning electron microscope, X-ray diffraction and transmission electron microscopy. By using 488nm laser, the properties of upconversion luminescence and energy transfer processes were studied in detail for the different concentration of erbium. The remarkable decrease of upconverted emission intensity and the quenching of the 2P3/2→4I9/2 and 2H9/2→4I13/2 transitions were observed in the Er:Y2O3 films with high erbium concentration. The absolute Up-Conversion Quantum Yield (UC-QY) of each film was measured for the UC emissions centered at 530 and 560nm at varying excitation power densities. UC-QY analysis has revealed that 2mol.% Er:Y2O3 film possess the highest total quantum yield of 4.07±0.1% with a power density of 15.3W/cm2. Moreover, the Er3+ luminescence analyzed in the IR region, shows 4I13/2 lifetimes was found to be 6.7ms for film deposited with 2mol% erbium. These results show that this film is promising as an efficient up-conversion layer suitable for many photonic applications.

Interfacial composition and adhesion of sputtered-Y2O3 film on ZnS substrate

Interface engineering has emerged as a fertile and efficacious approach to turn functional properties in the field of film systems. In this work, the interfacial properties of sputtered yttrium oxide films on zinc sulfide substrate (Y2O3/ZnS) were analyzed by transmission electron microscopy (TEM), X-ray photoelectron spectrum (XPS) depth profile and nano-scratch measurement. An interface layer with the depth of 20nm between Y2O3 film and ZnS substrate was directly observed by TEM. Under different film growth conditions, although the interfacial features including interfacial width and composition distribution exhibit similar behavior, it is found that higher cohesive strength is obtained under a special substrate bias voltage of −160V at low substrate temperature. Such an enhanced mechanical property can be understood by the role of physisorbed oxygen in the interfacial region, in which less physisorbed oxygen with van der Waals bonds leads to a strong adhesion. Our results provide a favorable strategy to achieve strong adhesion between oxide and sulfide at low temperature, which are urgent in future micro-electric applications.

Controllable phase formation and physical properties of yttrium oxide films governed by substrate heating and bias voltage

In order to understand the growth behavior of yttrium oxide films driven by thermodynamics and kinetics, two fundamental growth parameters, substrate heating and biasing, were investigated to control film structure and properties comprehensively. We observed two distinct areas, normal deposition area (area 1) and abnormal deposition area (etching area, area 2) at different substrate bias voltages regardless of the substrate temperature. X-ray diffraction (XRD) results show that heating promotes cubic phase formation, whereas ion bombardment induces monoclinic phase growth. Atomic force microscopy (AFM) measurements exhibit that the ions slightly enlarge the surface islands in area 1, whereas they flatten and smoothen the surface in area 2. X-ray photoelectron spectroscopy (XPS) results demonstrate that high temperature suppresses the physisorbed oxygen, and the ion bombardment favorably selects oxygen etching in area 1, causing excess oxygen vacancies. This selectivity almost disappears in area 2. Furthermore, the refractive index and band gap can be enhanced by both substrate temperature and bias voltage. The surface wettability of films can be modulated by the surface chemical composition.

The electronic state of thin films of yttrium, yttrium hydrides and yttrium oxide

Thin films of yttrium hydride have for almost 20 years been under investigation for optoelectronic and solar energy applications due to the hydrogen-induced switching in electronic state from the metallic elemental yttrium and yttrium dihydride to the transparent semiconductor material yttrium trihydride. In this study, we investigate the electronic structure of yttrium, yttrium hydride and yttrium oxide by using X-ray photoelectron spectroscopy and kelvin probe measurements. The investigated samples have been prepared by reactive sputtering deposition. We show that the electronic work function of transparent yttrium hydride is of 4.76eV and that the recently discovered photochromic reaction lowers the electronic work function of the transparent hydride by 0.2eV.

Formation of hydrated yttrium oxide and titanium oxide thin films by reactive sputtering in H2O atmosphere and their electrical properties

Hydrated yttrium oxide and titanium oxide thin films were prepared by reactive sputtering in H2O atmosphere at substrate temperatures from −30 to +130 °C. The electrical conductivities of the yttrium oxide films increased with decreasing substrate temperature. The increase in electrical conductivity corresponds well to the increase in IR absorption intensity due to OH bonds, and it is considered that proton conduction is dominant in the yttrium oxide films. In contrast, the conductivity of the titanium oxide films increased with increasing substrate temperature, suggesting that electron conduction is dominant in the films.

Thermoluminescence of Y2O3:Tb3+ thin films deposited by electron beam evaporation

Most thermoluminescent materials are created using crystal growth techniques; however, it would be of great utility to identify those few thermoluminescent materials that can be deposited using simpler methods, for example to be compatible with the early portions of a silicon integrated circuit or microelectromechanical fabrication process. In this work, thin films of yttrium oxide with a terbium impurity (Y2O3:Tb) were deposited on silicon wafers by electron beam evaporation. The source for the Y2O3:Tb was made by combining Y2O3 and Tb4O7 powders. The approximate thicknesses of the deposited films were 350nm. After deposition, the films were annealed at 1100°C for 30s to improve crystallinity. There is a strong correlation between the x-ray diffraction (XRD) peak intensity and the thermoluminescent glow curve intensity. The glow curve displays at least two peaks at 140°C and 230°C. The emission spectra was measured using successive runs with a monochromator set to a different wavelength for each run. There are two main emission peaks at 490nm and 540nm. The terbium impurity concentration of approximately 1mol% was measured using Rutherford backscattering spectrometry (RBS). The Y2O3:Tb is sensitive to UV, x-ray, and gamma radiation. The luminescent intensity per unit mass of UV irradiated Y2O3:Tb was about 2 times that of x-ray irradiated TLD-100.

Dielectric spectroscopy of electron beam deposited yttrium oxide films examined in metal–insulator–metal sandwich type structures

This report describes the dielectric properties of electron-beam deposited Y2O3 thin films examined in metal–insulator–metal-type structures fabricated onto quartz substrates. The dielectric measurements have been carried out in the frequency domain from 10mHz to 10MHz, with a frequency response analyser. Frequency characteristics of the complex capacitance, as well as Cole–Cole and Nyquist graphs, have been presented and discussed for the temperature range 398–523K. The results have been analyzed in terms of equivalent circuit models containing resistance–capacitance and constant phase elements (CPE). We have determined the values of the resistance, capacitance and CPE, which characterize the Y2O3 film and near-electrode regions. It has been shown that for high frequencies/low temperatures the dielectric properties are connected with Y2O3 film, while for low frequencies/high temperatures the dielectric response is dominated by the near-electrode regions. In the frequency range 0.1–10MHz the important contribution of series resistance of electrodes and leads has been observed.

Antireflective sub-wavelength structures on fused silica via self-assembly of silica

Antireflective sub-wavelength structures with high laser-induced damage threshold on fused silica are fabricated using a self-assembly technique, in which a porous yttrium oxide film is deposited as a mask followed by alkaline etching. By controlling the etching time, several sub-wavelength structures with different height, density and diameter have been made. The best reflectance is less than 2.87% for wavelengths from 300 to 1000nm after 1.5h etching. The laser-induced damage threshold of the etched glass measured by a 10ns Nd:YAG laser at a wavelength of 532nm was as high as 30J/cm2 compared to 16J/cm2 of blank glass. The specular reflectance of structures matches the theoretical simulation using a thin-film multilayer model, and the results reveal that the shape of the structures is similar to the calculated parabolic shape. Achieving antireflective sub-wavelength structures on fused silica paves the way for applications in laser systems.

Chemical bonding and optoelectrical properties of ruthenium doped yttrium oxide thin films

Highly infrared transparent conductive ruthenium doped yttrium oxide (RYO) films were deposited on zinc sulfide and glass substrates by reactive magnetron sputtering. The structural, optical, and electrical properties of the films as a function of growth temperature were studied. It is shown that the sputtered RYO thin films are amorphous and smooth surface is obtained. The infrared transmittance of the films increases with increasing the growth temperature. RYO films maintain greater than ∼65% transmittance over a wide wavelength range from 2.5μm to 12μm and the highest transmittance value reaches 73.3% at ∼10μm. With increasing growth temperature, the resistivity changed in a wide range and lowest resistivity of about 3.36×10−3Ωcm is obtained at room temperature. The RYO thin films with high conductivity and transparency in IR spectral range would be suitable for infrared optical and electromagnetic shielding devices.

Ion irradiation-induced phase transformation mechanisms in Y2O3 thin films

This work studies the ion irradiation-induced phase transformations in thin films of yttrium oxide. The films were deposited using an ion beam sputtering technique that allows the control of the order/disorder of the microstructure. As-deposited (disordered) and annealed (ordered) samples were irradiated by xenon ions at different energies and doses. Two different structural phase transformations were observed: cubic/amorphous-like and cubic/monoclinic. In both cases, it is shown that the pristine structure is of prime importance in the transformation process. The phase transformations are analysed in terms of structural extended defect nucleation originating from the oxygen network behaviour, which leads to polygonisation up to a nanocrystallite-like structure, followed by a phase transformation into a monoclinic structure.

Preparation and microstructural properties of erbium doped alumina–yttria oxide thin films deposited by aerosol MOCVD

Erbium-doped aluminum–yttrium oxide films (Er: Al2O3–Y2O3) were prepared by aerosol-UV assisted Metalorganic Chemical Vapor Deposition (MOCVD) at 410°C and annealed at 1000°C. The effects of humidity of carrier gas and UV-assistance on their structure and optical properties were investigated using scanning electron microscope, X-ray diffraction and Transmission electron microscopy. It was found that under low air humidity and without UV-assistance the films present a low mol% Al2O3 (10mol%) two different structural phases are observed corresponding to the cubic and the monoclinic structures of Y2O3. When the deposition takes place under high air humidity and with UV assistance the Er:Al2O3–Y2O3 films present a very high mol% Al2O3 (88mol%) and crystallize in the Y3Al5O12 (YAG) compound mixed with an amorphous phase. The Er3+ luminescence analyzed in the visible and IR regions, shows the classical green transitions. The best optical properties were obtained with the Er:Al2O3–Y2O3 films grown under high air humidity with UV-assistance. Under such deposition conditions, 4I13/2 lifetimes was found to be 1.1ms. This indicates that the deposition conditions, in particular air humidity, play an important role in the luminescent properties even after annealing.

Effects of post-deposition annealing ambient on band alignment of RF magnetron-sputtered Y2O3 film on gallium nitride

The effects of different post-deposition annealing ambients (oxygen, argon, forming gas (95% N2 + 5% H2), and nitrogen) on radio frequency magnetron-sputtered yttrium oxide (Y2O3) films on n-type gallium nitride (GaN) substrate were studied in this work. X-ray photoelectron spectroscopy was utilized to extract the bandgap of Y2O3 and interfacial layer as well as establishing the energy band alignment of Y2O3/interfacial layer/GaN structure. Three different structures of energy band alignment were obtained, and the change of band alignment influenced leakage current density-electrical breakdown field characteristics of the samples subjected to different post-deposition annealing ambients. Of these investigated samples, ability of the sample annealed in O2 ambient to withstand the highest electric breakdown field (approximately 6.6 MV/cm) at 10−6 A/cm2 was related to the largest conduction band offset of interfacial layer/GaN (3.77 eV) and barrier height (3.72 eV).

Direct extraction of carrier mobility in graphene field-effect transistor using current-voltage and capacitance-voltage measurements

Top gated graphene field-effect transistors were fabricated using yttrium oxide film as high-κ gate dielectric, and the gate voltage dependent drain current and gate capacitance characteristics were both measured on one graphene device. Based on the two kinds of data sets, we developed a method to extract the carrier mobility of graphene field-effect transistors, along with some other parameters, such as series resistance and residual carrier density. Prior to previous method, this method could well fit the transfer curve of graphene field-effect transistor with high gate oxide capacitance since its carrier concentration is directly obtained from the experimental data rather than from analytic equation.

Structural characteristics and optical properties of plasma assisted reactive magnetron sputtered dielectric thin films for planar waveguiding applications

Thin films of aluminum oxide (Al2O3), tantalum pentoxide (Ta2O5), titanium oxide (TiO2), yttrium oxide (Y2O3) and zirconium oxide (ZrO2) were deposited by plasma assisted reactive dual magnetron sputtering to determine their suitability as a host for a rare earth doped planar waveguide upconversion laser. The effect of deposition parameters such as cathode, plasma power and oxygen gas flows were studied and the operational working points were determined. Both power and lambda control were used to optimize the optical quality of each material. By using lambda control feedback system, the magnetron power fluctuates to sustain a fixed oxygen flow in the target area reducing the compound layer growth on the material and maintaining a healthy deposition rate. The optical properties, structure and crystalline phase of each film were found to be dependent on the process parameters. X-ray diffraction (XRD) analysis revealed that the thin films varied from amorphous to highly crystalline depending on the deposition conditions. X-ray photoelectron spectroscopy (XPS) was utilized for surface compositional analysis revealing that films had varying stoichiometric ratios which are controlled for each material by the deposition parameters chosen. The waveguide loss for the thin film layers was investigated and Ta2O5 was shown to have a slab waveguide loss of ~1dB/cm at both visible and infra-red wavelengths making it ideal for planar waveguide and laser applications. TiO2, Y2O3 and ZrO2 were found to deposit in a highly crystalline phase. Waveguiding in the TiO2 layers was not possible at 633nm or in the infrared region. The Y2O3 samples gave low loss (2–4dB/cm) at the 1.3 and 1.5μm wavelengths but no waveguiding at 633nm or 833nm was possible. Atomic force microscopy showed rough surface topography for TiO2, Y2O3 and ZrO2 akin to their crystalline growth with the SEM images confirming the regular crystalline columnar structure for the case of Y2O3 and ZrO2.

Yttrium oxide thin films prepared under different oxygen-content atmospheres: microstructure and optical properties

Yttrium oxide films were prepared on silicon wafers by reactive magnetron sputtering at different oxygen flow rates to investigate the microstructure and optical properties for desirable planar optical waveguiding applications. Under the different conditions of target surface, the deposition rate, structure, and optical properties have great changes. The deposition rate increases to the maximum, and then monotonically decreases. Oxygen content in films increases and the composition of films transforms from stoichiometry to an oxygen-rich state. Y2O3 films grow with the (222) preferred growth orientation at low oxygen flow rate, and then turn into the (622) orientation; the microstructure evolves from crystal structure to amorphous state as oxygen flow rate increases from 2 to 12 sccm. Sufficient oxygen makes films low-order structure and oxygen-rich films have poor crystallinity. Very smooth film has been obtained at oxygen flow rate of 12 sccm. The refractive index can be greatly modulated by the oxygen-content factor. It is convincing that the controllable structure and optical properties of Y2O3 films can be achieved by adjustment the oxygen flow rate for desired optical design and applications.

Evolution of composition, microstructure and optical properties of yttrium oxide thin films with substrate temperature

A series of yttrium oxide films has been fabricated on Si (100) wafers by different substrate temperatures based on reactive magnetron sputtering technology. And the evolution of composition, microstructure and optical properties of Y2O3 films has been investigated by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and spectroscopic ellipsometry (SE). It is shown that stoichiometric Y2O3 with much strong YO bond and cubic nanophase with larger size notably enhance the optical properties, especially refractive index. At low substrate temperature, the composition of Y2O3 films has nonstoichiometry feature accompanying with much physisorbed oxygen (Oδ) compared with these at high temperature. Increasing substrate temperature promotes the formation of YO bonds, approaching the stoichiometry with lower Oδ content. The film commences crystallizing at room temperature, and transformation of crystalline phase from monoclinic to cubic occurs, along with preferred (111) orientation and large grain as temperature increases. The results facilitate clear relationship between the characterizations of Y2O3 film and growth parameters, also, it can be realized that adjustment of optical constants of Y2O3 films in a large range having the aid of substrate temperature to obtain desirable composition and structure for optical applications.

Effects of post-deposition annealing ambient on Y2O3 gate deposited on silicon by RF magnetron sputtering

Effects of different post-deposition annealing (PDA) ambient [O2, N2O, N2, forming gas (95% N2-5% H2), and Ar] on the physical and metal–oxide–semiconductor (MOS) characteristics of yttrium oxide (Y2O3) films deposited on Si substrate by RF magnetron sputtering had been reported. X-ray diffraction (XRD) had revealed the presence of Y2O3 and yttrium silicate (Y2Si2O7) phases while Fourier transform infrared spectrometer (FTIR) had successfully identified chemical functional groups of Y-O, Si-O, and Si-Si. The detection of Y2Si2O7 phase and Si-O bondings by XRD and FTIR, respectively, had suggested the formation of interfacial layer comprising of Y2Si2O7 and SiO2. The MOS characteristics of annealed Y2O3 gate oxide in different ambient were then correlated with the physical results. It was perceived that O2 annealed sample had demonstrated the highest dielectric breakdown voltage as well as the lowest effective oxide charge, interface trap density, and total interface-trap density. Current conduction mechanisms that governed the leakage current in these gate oxides had also been established using a non-linear curve fitting method.