Growth of anodic oxide films on oxygen-containing niobium

Habazaki, H.; Ogasawara, T.; Konno, Hidetaka; Shimizu, K.; Asami, K.; Saito, Kan; Nagata, Shinji; Skeldon, P.; Thompson, G.E.

doi:10.1016/j.electacta.2005.03.011

Cited by 30 publications

(31 citation statements)

References 17 publications

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“…These films were anodized at a constant current density of 50 A m -2 in 0.1 mol dm -3 ammo nium pentaborate (ABE) electrolyte at 293 K, the potential being kept constant for 1 h at 50 V. After anodizing, specimens were heat treated in vacuum (5 × 10 -6 -10 -5 Torr) at 523 K for 1 h. A detailed study on the influence of thermal treatment in vacuum on morphological, compositional and electrical proper ties of anodic niobia films here investigated, has been reported in Refs. [25,26]. For this work it is necessary to mention that, according to the Transmission Elec tron Micrograph of ultramicrotomed sections as well as to the Glow Discharge Optical Emission Spectros copy (GDOES) analysis of the investigated film [26], the thickness of the aged Nb 2 O 5 before and after ther mal treatment was about 160 nm.…”

Section: Methodsmentioning

confidence: 99%

“…The deposited nio bium had a bcc structure with a [100] preferred orien tation [25]. These films were anodized at a constant current density of 50 A m -2 in 0.1 mol dm -3 ammo nium pentaborate (ABE) electrolyte at 293 K, the potential being kept constant for 1 h at 50 V. After anodizing, specimens were heat treated in vacuum (5 × 10 -6 -10 -5 Torr) at 523 K for 1 h. A detailed study on the influence of thermal treatment in vacuum on morphological, compositional and electrical proper ties of anodic niobia films here investigated, has been reported in Refs.…”

Section: Methodsmentioning

confidence: 99%

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A critical assessment of the Mott-Schottky analysis for the characterisation of passive film-electrolyte junctions

et al. 2010

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Abstract-The widespread use of the Mott-Schottky plots to characterize the energetics of passive film/electrolyte junction is critically reviewed in order to point out the limitation of such approach in describ ing the electronic properties of passive film as well in deriving the correct location of the characteristic energy levels of the junction. The frequency dependency of M-S plots frequently observed in the experimental data gathered in a sufficiently large range of frequency is extensively discussed for a relatively thick (160 nm) ther mally aged amorphous niobia (α Nb 2 O 5 ) film immersed in electrolytic solution. The relatively simple equiv alent electrical circuit describing an ideally blocking behaviour of the junction allows a direct comparison of the experimental data analysis based on the use of Mott-Schottky or amorphous semiconductor Schottky barrier interpretative models. Moreover the theoretical simulations of the M-S plots based on the theory of crystalline semiconductor suggest an electronic structure of the investigated passive film containing a distri bution of localized electronic states deep lying in energy in agreement with the model of amorphous semi conductor Schottky barrier.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

A critical assessment of the Mott-Schottky analysis for the characterisation of passive film-electrolyte junctions

et al. 2010

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“…However, there is a positive empirical correlation between  ox and  (Figure 1). Valve metals such as aluminum, [7][8][9][10][11][12][13] niobium, [14][15][16][17][18] and titanium [19][20][21][22][23][24][25] were alloyed in order to control the properties of anodic oxide films and improve their dielectric properties. The general trend in amorphous anodic oxide films is that their properties on binary valve metal alloys-including the relative permittivity and formation ratio-are the compositional averages of the respective alloy-constituting metals.…”

Section: Introductionmentioning

confidence: 99%

Enhanced Capacitance of Composite Anodic ZrO₂ Films Comprising High Permittivity Oxide Nanocrystals and Highly Resistive Amorphous Oxide Matrix

Habazaki

Koyama

Aoki

et al. 2011

ACS Appl. Mater. Interfaces

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Anodic oxide films with nanocrystalline tetragonal ZrO 2 precipitated in an amorphous oxide matrix were formed on Zr-Si and Zr-Al alloys and had significantly enhanced capacitance in comparison with those formed on zirconium metal. The capacitance enhancement was associated with the formation of a high-temperature stable tetragonal ZrO 2 phase with high relative permittivity as well as increased ionic resistivity, which reduces the thickness of anodic oxide films at a certain formation voltage. However, 2 there is a general empirical trend that single-phase materials with higher permittivity have lower ionic resistivity. This study presents a novel material design based on a nanocrystalline-amorphous composite anodic oxide film for capacitor applications.

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“…12 The XRD pattern of the Nb-50 atom % O films reveals only the broad peak of an amorphous structure, while following vacuum annealing films are transformed to crystalline NbO with a NaCl-type cubic structure ͑Fig. 1͒.…”

Section: Methodsmentioning

confidence: 99%

Suppression of Field Crystallization of Anodic Niobia by Oxygen

Habazaki

Ogasawara

Konno

et al. 2006

J. Electrochem. Soc.

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Solid-solution Nb-O films containing up to 50 atom % oxygen, prepared by magnetron sputtering, were used to investigate the influence of the oxygen on field crystallization during anodizing at 100 V in 0.1 mol dm −3 ammonium pentaborate electrolyte at 333 K. The findings reveal that field crystallization is hindered dramatically by addition of 20 atom % oxygen to the substrate, while no crystallization occurs for a Nb-50 atom % O substrate. Prior thermal treatment accelerates field crystallization of niobium, but not the Nb-50 atom % O substrate. The thermal treatment is considered to promote generation of precursor sites for crystal nucleation. However, sufficient oxygen in the substrate may restrict precursor development and/or reduce the compressive stresses in the amorphous anodic niobia that can facilitate crystal growth. Niobium is a potential alternative material to tantalum for electrolytic capacitors due to its many attractive properties 1 and its relatively high natural abundance. However, niobium capacitors are more susceptible to field crystallization during both growth of the anodic oxide dielectric and packaging of capacitors. Field crystallization in niobium and tantalum leads to degradation of the initial amorphous oxide, involving cracking and peeling due to growth of crystalline oxide, 2 which increases the leakage current. The effects are enhanced at increased anodizing temperatures and forming voltages.2-4 Inclusions 5,6 and roughness, especially convex surfaces, of the substrate assist crystal nucleation. 7,8 Recent studies using flat, inclusion-free, magnetron-sputtered niobium suggested nucleation is associated with precursor sites in the original, air-formed film, while incorporation of foreign species from the electrolyte or from the substrate at precursor regions can hinder nucleation.9 Other investigations indicate an enhanced susceptibility to field crystallization due to oxygen impurity in the substrate. 5,10,6,11 Oxide precipitates, possibly at grain boundaries, may be involved, although the detailed processes are not well understood. Here, the influence of oxygen in the substrate is examined on field crystallization of the anodic niobia. ExperimentalNiobium and Nb-͑20 and 50͒ atom % O films were deposited by sputtering 99.9% niobium in either argon or a mixture of argon and oxygen at ϳ0.1 Pa using magnetron sputtering enhanced with a radio frequency plasma source to increase the plasma density. Three types of flat substrate were employed: glass plates, silicon wafers, and electropolished and anodized aluminum sheets. Subsequent thermal treatment of the deposited films, either in air at 523-623 K for 1.8 ks or in vacuum ͑ϳ10−5 Pa͒ at 923 K, was employed selectively. Structures of the deposits were determined by X-ray diffraction ͑XRD͒ ͑Rigaku RINT 2000͒ using Cu K␣ radiation, with patterns obtained in an ␣−2 ͑␣ = 1°͒ mode.The films were anodized at 50 A m −2 to 100 V with current decay in stirred 0.1 mol dm −3 ammonium pentaborate electrolyte at 333 K. A platinum sheet was used as a...

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Growth of anodic oxide films on oxygen-containing niobium

Cited by 30 publications

References 17 publications

A critical assessment of the Mott-Schottky analysis for the characterisation of passive film-electrolyte junctions

A critical assessment of the Mott-Schottky analysis for the characterisation of passive film-electrolyte junctions

Enhanced Capacitance of Composite Anodic ZrO₂ Films Comprising High Permittivity Oxide Nanocrystals and Highly Resistive Amorphous Oxide Matrix

Suppression of Field Crystallization of Anodic Niobia by Oxygen

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Growth of anodic oxide films on oxygen-containing niobium

Cited by 30 publications

References 17 publications

A critical assessment of the Mott-Schottky analysis for the characterisation of passive film-electrolyte junctions

A critical assessment of the Mott-Schottky analysis for the characterisation of passive film-electrolyte junctions

Enhanced Capacitance of Composite Anodic ZrO2 Films Comprising High Permittivity Oxide Nanocrystals and Highly Resistive Amorphous Oxide Matrix

Suppression of Field Crystallization of Anodic Niobia by Oxygen

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Enhanced Capacitance of Composite Anodic ZrO₂ Films Comprising High Permittivity Oxide Nanocrystals and Highly Resistive Amorphous Oxide Matrix