Properties Of Anodic Oxide Films Research Articles

The influence of the growth rate on the semiconductive properties of titanium anodic oxide films

The semiconductive property of the anodic oxide films on titanium formed by potential sweep oxidation at various sweep rates is investigated by AC impedance in 0.1 mol dm −3 sulfuric acid solution. The dielectric constant and donor density of the oxide films change with the sweep rate. The dielectric constant increases and the donor density decreases with increase of the sweep rate. The dependence may be interpreted by the degree of hydration of the film. The oxide film formed by the higher sweep rate is more hydrated. High content of the hydrating water or an OH − bridge in the film may introduce a relatively high dielectric constant and low donor density.

湿式法による化合物薄膜の作製・構造と物性 チタンのアノード酸化物薄膜の構造と物性

湿式法による化合物薄膜の作製・構造と物性 チタンのアノード酸化物薄膜の構造と物性

Inter–relationships between ionic transport and composition in amorphous anodic oxides

The inter–relationships of alloy composition, film composition and ionic transport for formation of amorphous anodic oxide films are addressed quantitatively through systematic study of sputter–deposited Al–Ta alloys containing up to 39 at.% Ta. The work reveals the dependence of electric field, ionic transport number, incorporation of species into the anodic film at the alloy–film interface and mobility and distribution of species within the anodic film on alloy composition. Anodic oxidation, at high current efficiency, of alloys containing 2.8, 15, 32 and 39 at.% tantalum results in formation of two–layered anodic films by migration of cations outwards and by migration of anions inwards: an outer layer, 20% or less of the total film thickness, composed of relatively pure alumina and an inner layer containing units of Al2O3 and Ta2O5 distributed relatively homogeneously. Two–layered films develop due to the slower migration rate of Ta5+ ions relative to A13+ ions in the inner layer of the growing anodic films, which changes progressively from about 0.6 for dilute alloys to about 0.9 for Al–39 at. per cent Ta. The average nm V−1 ratios, total transport numbers of cations and average Pilling–Bedworth ratios for the films change almost linearly with alloy composition between the values for anodic alumina and anodic tantala. A tantalum–enriched layer, about 1 nm thick, is formed in the Al–2.8 at.% Ta and Al–15 at.% Ta alloys just beneath the anodic film, indicating prior oxidation of aluminium in the initial stages of anodizing. In contrast, aluminium and tantalum in the alloys containing more than 30 at.% tantalum are immediately incorporated into anodic films in their alloy proportions, without development of a tantalum–enriched layer, at the available resolution. Boron species, incorporated from the electrolyte into the outer parts of the films, are immobile in films on alloys up to 15 at.% Ta but migrate outwards in other films, possibly due to the increased Lorentz field. Though the inter–relationships between film parameters and alloy composition are established for Al–Ta alloys specifically, the findings are considered to be equally relevant to amorphous anodic oxides formed on alloys and semiconductors generally.

Anodization behavior of Al, and physical and electrical characterization of its oxide films

We have investigated the physical and electrical properties of anodic oxide films treated by a variety of aqueous electrolyte solutions. All anodic oxide diodes revealed consecutive current regimes varying with bias voltage as V, V2, and Vn (n≳2) in the steady-state current-voltage characteristics. Here, the transition voltage from the V2 to Vn current regime and the voltage exponent n varied depending on the oxide forming electrolyte and the bias direction of the diodes. These electrical properties were interpreted as a space-charge-limited current modified by a distributed gap state density in space and in energy. The oxide had a double-layer structure, a layer containing an anion characteristic of each electrolyte and an anion-free layer. The anion-containing layer had a varying gap state distribution. This was due to the anion characteristics, which reduce a deep-lying gap state density and modify a tail state density. We propose two practical anodizing techniques to control the depth profile of the anion. This allows us to form an oxide with a small leakage current equivalent to an anion-free control oxide. We also show that the dielectric loss for the anion-free oxide was reduced through the formation in an organic electrolyte and was increased in an inorganic electrolyte.

Dielectric properties of anodic oxide films on tantalum

The electrochemical behaviour of Ta-TaO x structures was investigated by impedance spectroscopy. It was shown that, after the polishing treatment, the electrode is covered by an “initial” oxide film containing tantalum monoxide, TaO, and that “electrogenerated” oxides are only composed of tantalum pentoxide, Ta 2O 5 (⩾ 97 mol%). However, the dielectric properties of the structures strongly depend on the thickness of the oxide, d ox , because of the influence of a sub-stoichiometric oxide of TaO in thin layers, in agreement with previous results obtained by XPS measurements. The variation of the reciprocal total capacitance of the oxide, C ox , with the quantity of electricity, Q a , involved in the formation of the oxide exhibits two linear parts. The breakdown of the slope of that curve is interpreted by a variation of the relative permittivity, ε r , of the oxide with its thickness: for thin films ( d ox ⩽ 19nm), ϵ r ≈ 18.5 and for thick films ( d ox > 19 nm) ϵ r ≈ 27.5.

The effect of temperature on the growth of anodic oxide film on titanium

The effect of temperature on the growth and properties of anodic oxide films on titanium has been studied by electrochemical and impedance measurements combined with solution analysis by inductively coupled plasma emission spectrometry. Under potentiostatic conditions, the current efficiency is almost close to unity in the early film growth stage, but beyond this stage, significant film dissolution occurs. The charge for l h film growth was determined from the difference between the total charge passed and the charge equivalent to titanium ions dissolved in the solution; the charge for film growth increases linearly with potential. The reciprocal capacitance of the film also has a linear dependence on potential. By using these data, the dielectric constant for the anodic film was estimated. The dielectric constant increases with temperature and the value of the dielectric constant for the film formed at 323 K or 333 K is close to that for anatase, suggesting that the anodic films formed above 323 K became crystalline.

Photoelectrochemical Properties of Anodic Oxide Film on Niobium

Photoelectrochemical properties of niobium oxide film formed by anodic oxidation in a saturated boric acid solution have been studied. The oxide film is considered as an n-type semiconductor from the polarization curves measured in 0.5 N sulfuric acid solution. Anodic photocurrent is observed when the oxide film is illuminated by an ultraviolet light while it is anodically polarized. From the spectrum of the photocurrent of the film, the band gap energy of the oxide is determined to be about 3.3 eV. When the specimen is polarized at a cathodic potential before the photocurrent measurements, the film shows an additional photoresponse for the light with longer wavelength than that corresponds to the band gap energy. This can be explained by the formation of new electron levels in the band gap by cathodic hydrogen charging

ChemInform Abstract: The Influence of Growth Rate on the Properties of Anodic Oxide Films on Titanium.

ac Impedance measurements and photocurrent spectroscopy have been used to examine the dependence on growth rate of the solid state properties of thin (<20 nm) anodic oxide films on titanium. At room temperature, the relative permittivity and defect concentration profiles in the oxide were found to depend markedly on growth rate. The effects on the photocurrent of recombination and trapping were most pronounced when the films are grown rapidly. It was found that the high defect densities associated with rapidly grown oxide films could be decresed by growing or annealing the oxide films at higher temperatures.

The influence of growth rate on the properties of anodic oxide films on titanium

ac Impedance measurements and photocurrent spectroscopy have been used to examine the dependence on growth rate of the solid state properties of thin (<20 nm) anodic oxide films on titanium. At room temperature, the relative permittivity and defect concentration profiles in the oxide were found to depend markedly on growth rate. The effects on the photocurrent of recombination and trapping were most pronounced when the films are grown rapidly. It was found that the high defect densities associated with rapidly grown oxide films could be decresed by growing or annealing the oxide films at higher temperatures.

Electrochemical and Optical Properties of Anodic Oxide Films on Titanium

Ellipsometric and electrochemical techniques are used to study the anodic oxidation of titanium in aqueous and nonaqueous electrolytes. Transparent oxide films with a refractive index of 2.48 grown on electropolished surfaces exhibit ideal valve‐metal behavior up to a thickness of approximately 30 nm. Beyond this thickness the refractive index and low‐frequency dielectric constant of the film both decrease, but thicknesses of 100 nm can be achieved prior to complete breakdown under suitable experimental conditions. Open‐circuit transients are used to determine the relation between the current density and the electric field in the oxide film. At an anodization current density of 325 μA/cm2 the field in the film is found to be 0.484 V/nm, and the value of B in the dependence of current density on field, , is found to be 22.1 nm/V. There is some evidence that the current is controlled by the effective field in the oxide film and hence is sensitive to field‐induced variations in the dielectric constant. Electrostriction is found to affect titanium oxide to about the same extent as other valve‐metal oxides. If the current is made cathodic prior to film breakdown, the insertion of hydrogen into the film causes the initially transparent oxide to absorb light. If the hydrogen that enters the film is assumed to be uniformly distributed, a value of 0.1 is calculated for the optical extinction coefficient when the hydrogen concentration reaches its limiting value. There is evidence that the distribution of hydrogen within the oxide film is not uniform, and that it may penetrate only the outer 10% of thicker films that have not broken down. The alteration in film structure resulting from breakdown produces marked changes in both the cathodic process and the optical behavior.

An ellipsometric investigation of nickel oxide films in alkaline solution: The multilayer film approach

The properties of anodic oxide films formed on polycrystalline nickel electrodes in alkaline solution under potentiodynamic conditions were studied by means of cyclic voltammetry and combined ellipsometry and reflectometry. The oxide film grown on a Ni surface during the potential scan between hydrogen and oxygen evolution was revealed to be optically inhomogeneous. In this paper a reliable model for two- or three-layer oxide films with different refractive indices is demonstrated. It has been found that Ni(II) oxides form a bottom thin solid state film (final thickness of about 3 nm) of n ̂ 3=2.50(±0.15) -0i (the mean value for λ=632.8 nm) composed of NiO and Ni(OH) 2 phases. At higher anodic potentials a further oxidation of Ni(II) oxides and the formation of thick layers of Ni(III) and Ni(IV) phases on top of the passive film occurs, most probably, due to a defect mechanism. The obtained values of the refractive indices are: n ̂ 2=1.41(±0.01)−0.073(±0.005)i and n ̂ 1=1.38(±0.01)−0.06(±0.01)i for oxide film layers containing socalled β-NiOOH and γ-NiOOH hydrous nickel oxide species, respectively.

An ellipsometric investigation of nickel oxide films in alkaline solution: The multilayer film approach

Abstract The properties of anodic oxide films formed on polycrystalline nickel electrodes in alkaline solution under potentiodynamic conditions were studied by means of cyclic voltammetry and combined ellipsometry and reflectometry. The oxide film grown on a Ni surface during the potential scan between hydrogen and oxygen evolution was revealed to be optically inhomogeneous. In this paper a reliable model for two- or three-layer oxide films with different refractive indices is demonstrated. It has been found that Ni(II) oxides form a bottom thin solid state film (final thickness of about 3 nm) of n 3 =2.50(±0.15) -0i (the mean value for λ=632.8 nm) composed of NiO and Ni(OH)2 phases. At higher anodic potentials a further oxidation of Ni(II) oxides and the formation of thick layers of Ni(III) and Ni(IV) phases on top of the passive film occurs, most probably, due to a defect mechanism. The obtained values of the refractive indices are: n 2 =1.41(±0.01)−0.073(±0.005)i and n 1 =1.38(±0.01)−0.06(±0.01)i for oxide film layers containing socalled β-NiOOH and γ-NiOOH hydrous nickel oxide species, respectively.

Properties of anodic oxide films prepared on nitrogen-doped tantalum films

Capacitors prepared from thin films of tantalum nitride, which has an h.c.p. structure, show various excellent electrical properties. TaN capacitors, in particular, exhibit great endurance to heat treatment and have no polarity in their anodic and cathodic leakage currents. The structure of these anodic films, their dielectric properties and their electrical conduction characteristics were studied. An anodic film formed on a nitrogen-doped tantalum film was shown to consist of two layers by analysis using the chemical etching method and by Auger electron spectroscopy. The first layer, which is situated at the oxide-electrolyte interface, has a high density and includes very little nitrogen. The second layer is porous and contains excess nitrogen.

Properties of anodic oxide films on n-type GaAs, GaAs 0.6P 0.4 and GaP

Oxide layers were grown anodically on n-type GaAs, GaAs 0.6P 0.4 and GaP using a 3% aqueous solution of tartaric acid in propylene glycol as electrolyte. The oxide films were examined by secondary ion mass spectrometry and ellipsometry before and after annealing in nitrogen at 400°C. The results show that anodic oxide films on III–V compound semiconductors are composed of several oxide layers. Capacitance-voltage measurements on metal-oxide-semiconductor diodes prepared with anodic oxides revealed electrical instabilities such as a frequency dispersion and a field-induced hyeteresis. These anomalies can be explained by imperfections of the oxide-semiconductor interface.

Optical properties of anodic oxide films on GaAs by ellipsometry

Optical properties of anodic oxide films on GaAs by ellipsometry

The Mechanical Properties of Anodic Oxides and their Influence on Fatigue Behaviour of Aluminium Alloys

Studies have been made on certain properties of anodic oxide films on aluminium: modulus and fracture strains. The effect of the films on substrate fatigue behaviour has also been studied. The tech...

Properties of Anodic Oxide Films Formed in the Anodization of Silicon Nitride

The anodization of silicon nitride films on silicon has been characterized using ellipsometry. Calculations made indicate that the sensitivity of ellipsometry to the anodization depends on the initial silicon nitride thickness. Ellipsometry data obtained during stepwise anodization are consistent with a model of two layers on silicon where the anodic oxide layer grows at the expense of the silicon nitride. The thickness ratio of oxide produced to silicon nitride used falls within ±0.25 of the theoretically expected value, 1.81, and depends to some extent on anodization conditions. The refractive index and growth properties of the oxide are similar to those of anodic oxides of silicon. Stepwise etchback studies on the oxide give results which are consistent with the anodization data and which indicate an abrupt silicon nitride‐anodic oxide interface.

Defect photoconductivity of anodic Ta2 O5 films

Photoconductive properties of anodic oxide films grown on β-Ta films have been measured at room temperature as a function of incident wavelength between 1000 and 500 nm (1.2–2.5 eV). Analysis of the spectral response of photoconductivity on thick (5200 Å) and thin (800 Å) oxides indicates the presence of a defect conduction band edge energetically at 1.5 eV below the oxide conduction band.

陽極酸化による金属心酸化物被覆印刷配線板の研究

A study was made on a method of preparing a printed Wiring board clad with metal core oxidation. Mechanisms of rectification and breakdown were investigated for preventing rectification, lowering of electrical resistivity, and breakdown of anodic oxide film under high humidity. The sealing with boiling water or high pressure steam and anodic re-oxidation in 3wt% ammonium borate bath were conducted in order to improve the electric properties of anodic oxide film formed in 10wt% H2SO4 bath.The results obtained were as follows.(1) It was considered that the rectification, the lowering of electrical resistivity, and the breakdown of the film under high humidity were due to the interactions between adsorbed water and impurities contained in its micro-porous structure.(2) The rectification of film decreased by sealing with boiling water, and its breakdown voltage increased to 500V or higher by sealing with high pressure steam of 3 or 6kg/cm2.(3) The electrical resistivity was improved up to 5×1012 Ω cm by anodic re-oxidation in 3wt% ammonium borate and sealing with high pressure steam.(4) Insulation and wiring were successful by using selective anodic oxidation method.

Electrical Properties of Anodic Oxide Films of Ta, Nb, Zr, Ti, W, and V Formed by the Ion‐Cathode Method

Amorphous oxide films have been grown on Zr, Ti, W, Ta, Nb, and V by ionized gas anodization using the ion cathode as a source of negative ions. Films were grown on each metal at constant current to 175V followed by constant voltage for about 4 hr. Several electrical and optical properties were measured for the anodic films produced on these refractory metals. Resistivities of the anodic oxide films on Zr, Ti, W, Ta, Nb, and V ranged from 1014 to 1017 ohm‐cm. Breakdown voltages with the refractory metal positive (gold contact negative) were of the order of 31V to 111V. Film capacitances for these metals varied between 0.031 and 0.050 µf/cm2, and the dissipation factors averaged 0.015 for all the oxides except V which was 0.062. Thicknesses and refractive indices were obtained by ellipsometry for anodic films on Ta and Nb. Film thicknesses were respectively 0.61µ and 0.57µ for Ta and Nb whereas the refractive indices were 2.1 and 2.0. Dielectric constants calculated from capacitance measurements for these anodic films were 22 and 28, respectively. The properties of films prepared by the ion cathode method are compared with those produced by plasma and solution methods reported by others.