Properties Of Metal Oxide Films Research Articles

Effects of atmosphere composition during direct ultraviolet-light patterning of solution-deposited In2O3 thin film transistors

Sol-gel synthesis is widely used to fabricate metal oxide thin films by solution, but it requires high-temperature thermal annealing to fully convert precursors to metal oxides. Exposure to Ultraviolet (UV) light before thermal annealing of precursor films has been shown to reduce the conversion temperature, with the added benefits of film patterning when done through a shadow mask and improved device performance. However, the mechanism by which UV exposure under different atmospheric compositions affects the properties of metal oxide films after thermal annealing has not been investigated. Here, we control the atmospheric composition during UV-patterning—prior to high-temperature thermal annealing—of In2O3 sol-gel films which serve as the semiconductor in thin-film transistors. Despite all films being annealed at 250°C in air after UV patterning, films exposed to UV under oxygen-containing atmospheres have higher metal-oxygen-metal bonding and exhibit higher transistor mobility compared to the films exposed to UV under N2 atmosphere. The origin of the effect of atmospheric composition on mobility is studied through X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared spectroscopy and is revealed to be the result of the reformation of the nitrate species in the films under more oxidizing atmospheres during UV exposure. These nitrates can be completely removed by thermal annealing, facilitating more complete metal-oxygen-metal bond formation, which is reflected in higher OI XPS signal and transistor mobility. In contrast, films processed under N2 atmosphere during UV exposure contain nitrite species that cannot be removed by thermal annealing, resulting in less metal-oxygen-metal bond formation and lower mobility.

Electrophysical Properties of Metal Oxide Films Fabricated by Using Spray Pyrolysis

This document describes the technology of manufacturing metal oxide films ZnO, SnO2, Zn2SnO4 from aqueous solutions of the corresponding salts by spray pyrolysis. The modes and conditions of deposition of metal oxide films on hot (420 °C) glass substrates are given. The electrical parameters of the films were measured by the van der Pau method and by the Hall effect, the surface resistance was in the range from 140 to 85⋅103 Ohm/. The band gap was determined by light absorption spectra and was within 3.2...3.5 eV. For all metal oxides, the n-type conductivity was determined using the thermosonde and the Hall effect.

Local lattice distortions in oxygen deficient Mn-doped ZnO thin films, probed by electron paramagnetic resonance

The structure and functional properties of metal oxide films for device applications are largely affected by oxygen vacancies. While the macroscopic relationship between functionality and oxygen supply during growth is easy to access, the local influence of changing oxygen content on the incorporated metal atoms has been rarely investigated. As a model system, we use Mn as a local probe in hetero- and homoepitaxial ZnO thin films for electron paramagnetic resonance (EPR). Mn is expected to be incorporated as Mn2+ in the Zn-lattice site of ZnO films grown in a wide range of oxygen partial pressures. The zero field splitting (ZFS) parameter D depends on the crystallographic c/a ratio of ZnO : Mn lattice constants as it measures the trigonal distortion of oxygen tetrahedra at the Zn2+ site with respect to the Mn2+ site. The ZFS parameter D correlates linearly with displacement of Mn2+ ions along the c-axis in the MnO4 tetrahedra and the corresponding bond lengths between the Mn2+ ions and the axial oxygen ion.

Features of formation of metal oxide thin film layers in a gas-sensor structure Pt/WO x /SiC by means of pulsed laser deposition

The effect of regimes of reactive pulsed laser deposition (PLD) of WOx thin films on gas sensing performance of a metal-oxide-silicon carbide device potentially applicable for monitoring explosive gases, in particular, hydrogen, and environmentally harmful gases at elevated temperatures was investigated. The films were deposited from a tungsten target in oxygen at room temperature and subjected to high-temperature annealing. The features of the film deposition under free laser plume expansion and the deposition of the plume scattered in a buffer gas were considered. Weak differences in the structural and chemical state of the WOx films arising from the variation of the deposition conditions had a significant influence on the properties of the sensor. Deposition of WOx by the scattered plume at an oxygen pressure of ∼10 Pa made it possible to increase the value of the sensor response to hydrogen at temperatures of 150 to 500°C by more than one order of magnitude. Mathematical modeling of the dynamics of the laser plume expansion from the W target at a given oxygen pressure allowed identifying the factors that have significant influence on the properties of metal oxide films fabricated using various schemes of PLD.

Role of surface OH groups in surface chemical properties of metal oxide films

We investigated the effects of surface OH groups on surface chemical properties, such as wetting and surface reactivity of various metal oxide films. Linear relationship was observed between hydrophobicity caused by adsorption of organic substances from the atmosphere and surface OH group density. It was also found that surface reactivity with a fluoroalkyl isocyanate silane was strongly dependent upon the surface OH group density of the film. These results indicate that surface OH groups are a major factor governing the surface chemical properties of the films. It was also revealed that the surface OH group density depended on the film materials. This dependence can be explained in terms of electronegativity of the metal element directly bound to oxygen atoms. Utilizing these findings, the surface chemical properties of SiO 2 films were successfully controlled.

Optical properties of indium tin oxide and fluorine-doped tin oxide surfaces: correlation of reflectivity, skin depth, and plasmon frequency with conductivity

Variable angle reflectance FTIR was used to investigate the reflectance of thin films of either indium tin oxide (ITO) or fluorine-doped tin oxide (SFO) on glass substrates in the mid-IR. The reflectance was observed to depend on the incident angle, wavenumber, and the polarization used. The Drude model and the Fresnel equations for reflection at a single dielectric boundary were used to interpret these results in terms of the conductivity, reflectivity, skin depth, and plasmon frequency of the metal oxides. The skin depth of thin film ITO electrodes was found to depend on the sheet resistance linearly, while the reflectance varied according to the square root of the sheet resistance. The method shows that an optical probe can be used to determine the electrical properties of metal oxide films in a noninvasive approach.

An apparatus for the measurement of internal stress and thermal expansion coefficient of metal oxide films

A measuring apparatus based on a phase shifting interferometry technique to determine the mechanical properties of metal oxide films was presented. Thin films were prepared by ion-beam sputter deposition at low substrate temperature. Quantitative determination of the mechanical properties such as the internal stress, biaxial elastic modulus, and thermal expansion coefficient of metal oxide films were investigated. A phase shifting Twyman–Green interferometer with the phase reduction algorithm was setup to measure the temperature-dependent stress in thin films. Two types of circular glass plates, with known Young’s moduli, Poisson’s ratios, and thermal expansion coefficients, were used as coating substrate. The temperature-dependent stress behavior of the metal oxide films was obtained by heating samples in the range from room temperature to 70 °C. The stresses of thin films deposited on two different substrates were plotted against the stress measurement temperature, showing a linear dependence. Four oxide films were reported for their film stresses and thermal expansion coefficients.

Surface OH group governing adsorption properties of metal oxide films

Time-of-flight secondary ion mass spectrometry, X-ray photoelectron spectroscopy and contact angle measurements were applied to investigate the relationship between the adsorption of organic substances from the atmosphere and the surface OH group density of metal oxide films deposited onto glass by r.f. reactive magnetron sputtering. The amount of adsorbed carbon substances on the films is dependent on the surface OH group density of the films. This fact indicates that the surface OH group density is a major factor governing the adsorption of organic substances from the atmosphere on the films. It is also found that the surface OH group density is dependent on the film materials. This dependence is explained with respect to the electronegativity of the metal element directly bound to oxygen atoms.

Determination of the acid-base properties of metal oxide films and of polymers by contact angle measurements

The surface isoelectric point for native air-formed oxide films on various metals has been determined by measurement of contact angles at the hexadecane/ aqueous solution interface as a function of the pH of the aqueous phase. Application of Young's equation, the Gibbs equation, and surface equilibria conditions for hydroxylated oxide films leads to a mathematical expression which shows that the contact angle goes though a maximum at the isoelectric point of the oxide. The experimentally determined values for the oxide films on aluminum, chromium, and tantalum are within one to three pH units of the reported isoelectric points for the corresponding bulk oxide powders. The surface isoelectric point of an oxide-covered Ta-implanted A1 surface lies between that of Al2O3 and Ta2O5. The acid-base properties of various polymers, including a commercially available pressure-sensitive adhesive, were determined by measuring the contributions γS + and γS - to the solid surface free energy using the contact angle approach of van Oss and Good. Adhesion measurements for a pressure-sensitive adhesive having a positive surface charge show that the peel strength is greatest when the metal substrate has a surface oxide film of basic character.

Mechanical Properties of Metal Oxide Films

A brief review is given of mechanical property measurements on oxide films. This review is followed by a detailed discussion of the mechanical and fracture properties of anodic aluminum oxide films as observed in the author's laboratory. Extensive measurement of Young's modulus, ,and fracture strain, , for separated films 3000Aå thick is reported as a function of environmental water vapor pressure. The fracture of these unsupported films is shown to occur by a brittle mechanism. Mechanical properties of adhering aluminum oxide films are given as a function of their thickness. These oxides were observed to fracture either at slip steps, or at right angles to the tensile axis in a regularly spaced fashion. A theory of adhering oxide fracture is discussed which accounts well for the observations. An equation which describes the spacing of regular oxide fracture cracks as a function of substrate strain ε is given in the form , where () are the initial conditions for regular fracture, is the oxide thickness, and is a constant.