Alumina Barrier Layer Research Articles

In situ spectroscopic ellipsometric study of porous alumina film dissolution

Porous alumina films have been synthesised by anodisation of high purity aluminium in 0.4 M phosphoric acid at constant current density. The dissolution process of those coatings in 2 M phosphoric acid has been investigated by in situ spectroscopic ellipsometry (SE) combined with electrochemical measurements. A sharp drop of the open current potential is observed due to film removal. The dissolution time depends on total barrier layer thickness. Those results are confirmed by SE measurements. A three layer optical model has been used to interpret SE spectra. During the dissolution process, the porous top layer has a quasi-constant thickness, whereas porosity increases significantly. The dissolution proceeds within the pores. Only the thickness of pure alumina barrier layer (upper part) decreases during the dissolution process whereas the interface barrier layer (lower part) does not change.

Investigation of Alumina Barrier Layer for FeRAM Prepared by rf Magnetron Sputtering Method

Alumina thin films as hydrogen barrier layer for FeRAM were prepared by rf magnetron sputtering method using a ceramics target and then investigated. RF power, sputtering pressure, oxygen partial pressure and so on were varied as experimental conditions. Fundamental properties of alumina thin films such as refractive index were primarily investigated. Highly oxidized films can be obtained under the condition with oxygen as a sputtering gas. Ferroelectric capacitors coated by alumina films were annealed in forming gas and also characterized in term of ferroelectric properties. Pt/PZT/Pt/Ti/SiO 2 /Si structured capacitor coated with highly oxidized alumina represented good ferroelectric properties even after the forming gas annealing.

Investigation of Alumina Barrier Layer for FeRAM Prepared by rf Magnetron Sputtering Method

Alumina thin films as hydrogen barrier layer for FeRAM were prepared by rf magnetron sputtering method using a ceramics target and then investigated. RF power, sputtering pressure, oxygen partial pressure and so on were varied as experimental conditions. Fundamental properties of alumina thin films such as refractive index were primarily investigated. Highly oxidized films can be obtained under the condition with oxygen as a sputtering gas. Ferroelectric capacitors coated by alumina films were annealed in forming gas and also characterized in term of ferroelectric properties. Pt/PZT/Pt/Ti/SiO 2 /Si structured capacitor coated with highly oxidized alumina represented good ferroelectric properties even after the forming gas annealing.

Fabrication and characterization of single layer and multi-layer anodic alumina membranes

Porous alumina films containing parallel capillary pores of uniform size were fabricated by anodically oxidizing high purity aluminum films in phosphoric acid and sulfuric acid solutions. These films were formed into membranes by post-oxidation processing that removes unoxidized aluminum as well as a barrier layer of alumina from the base of the pores. Symmetric membranes were made by oxidizing at constant current density conditions. Two layer composite membranes were made by changing current density during the oxidation process. The thickness, pore density and porosity of each membrane were predicted from the relationships between structural characteristics and processing conditions that were developed in previously reported kinetic studies of anodic oxidation of aluminum. Each membrane was then characterized using permeability measurements. The hydraulic permeability of membranes formed in phosphoric acid and the diffusive permeability of membranes formed in sulfuric acid were measured. A comparison of the measured permeability values to those predicted using the structural characteristics calculated using relationships developed in the kinetic studies shows excellent agreement. These results illustrate that porous alumina membranes can be fabricated with transport characteristics that can be predicted from the processing conditions used during membrane formation.

Ordered Two-Dimensional Nanowire Array Formation Using Self-Organized Nanoholes of Anodically Oxidized Aluminum

Self-organization of a two-dimensional array of nanoholes which were formed by anodic oxidation of aluminum was investigated quantitatively using fast Fourier transformation (FFT) analysis of scanning electron microscopy (SEM) images. The highly ordered array of nanoholes with diameters of 26 nm was obtained by two-step anodization at anodic voltage around 40 V, and oxalic acid concentration of 0.5 M. A two-dimensional ordered array of Au free standing nanowires was successfully fabricated by the deposition of Au using DC electroplating in nanoholes of aluminum oxide, by removal of the aluminum oxide barrier layer using wet chemical etching. The present method has a high efficiency to fabricate ordered nanowire array of a variety of conductive materials in a large area, and wide applications for fabricating quantum effect devices and materials would be expected.

Preparation of a tubular anodic aluminum oxide membrane

An anodic aluminum oxide tube with perforated straight pores to use as a porous membrane or as a support for a composite membrane was prepared. An aluminum oxide layer with straight micropores closed by an oxide barrier layer was formed on the surface of an aluminum tube, 45 mm long, 0.5 mm thick and 6 mm in outer diameter, by anodic oxidation in an aqueous solution of oxalic acid. The pores were opened by dissolution of the inner aluminum and the subsequent barrier layer of aluminum oxide. The tubular alumina membrane obtained was 35–40 μm thick with straight micropores of 20–50 nm, and therefore showed Knudsen permselectivity for inorganic gases. It was found that the tube could withstand at least up to 4.4 atm of transmembrane pressure.

Alumina barrier layers on LCD glass

Abstract Effective diffusion coefficients, D e , for the movement of sodium from an LCD glass into a sputtered alumina barrier layer have been determined. Secondary ion mass spectrometry analysis was used to measure sodium concentrations in 100 nm thick alumina films on soda lime glass at 520°C and for similar films on alkaline earth boroaluminosilicate glass at 650°C. Calculated values of D e are compared with extrapolated values of the diffusion coefficient, D , for sodium in polycrystalline alumina. The agreement is inconsistent. This is explained in terms of the countercurrent of hydrogen ions needed to maintain charge neutrality when a sodium ion moves out of the glass into the alumina film.

Scanning tunneling microscopy of metal surfaces in air

We have constructed a scanning tunneling microscope (STM) for operation in air. We obtained surface images of a commercial titanium (Ti) plate, a barrier layer of anodic aluminum oxide (Al 2O 3) and platinum (Pt) fine particles supported on a TiO 2/Ti plate. We found the following results: (1) The resolution of our STM is better than 10 Å in air. (2) The surface image of the barrier layer has a somewhat complicated structure compared with hexagonal cells observed by SEM. (3) The surface of Pt fine particles is flat and shows a sharp and deep cliff down to the TiO 2/Ti plate.

Discussion of “Some Evidence for Duplex Film Structuring Within the Anodic Alumina Barrier Layer” [G. A. Dorsey, Jr. (pp. 466–471, Vol. 116, No. 4)

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Closure to “Discussion of ‘Some Evidence for Duplex Film Structuring Within the Anodic Alumina Barrier Layer’ [G. A. Dorsey, Jr. (pp. 466–471, Vol. 116, No. 4)

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Some Evidence for Duplex Film Structuring Within the Anodic Alumina Barrier Layer

Direct observations of anodic barrier layer oxide, by transmission electron microscopy, provide further evidence for the duplex film structuring suggested earlier, based on infrared data. Anodic films were prepared with a boric acid electrolyte maintained at 60°C and two film layers were observed: the uppermost layer being extremely thin. Only the layer lying next to the metal (primary phase barrier layer) showed a thickness relationship with respect to forming voltage: 14.8 Aå/v. The thickness of the uppermost layer (secondary phase barrier layer) was on the order of 200Aå and was essentially independent of forming voltage. With the boric acid electrolyte employed at 90° C, a pronounced increase was found in the thickness of the uppermost layer. The thickness of the layer next to the metal surface remained consistent with the ∼14 Aå/v relationship. Infrared, coating weight, effluent gas detection, and impedance data were also obtained for these coatings and correlated with the data obtained by transmission electron microscopy.