Reassessment of degradation mechanisms in anodic tantalum oxide capacitors under high electric fields

Su, Xin; Viste, Mark; Hossick-Schott, Joachim; Yang, Lei; Sheldon, Brian W.

doi:10.1007/s10853-014-8656-7

Cited by 2 publications

(3 citation statements)

References 26 publications

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“…For capacitor application of Ta and Nb, a main effort has been directed to reduce the oxygen impurity in Ta and Nb, since the oxygen impurity often induce the crystallization of amorphous anodic oxides [44,45]. For Ta and niobium, crystallization is detrimental because of the increase in the leakage current and enhanced bias dependence of the capacitance [46][47][48]. In contrast, the findings in the present study demonstrate that the oxygen incorporation must be promoted for capacitor application of the Zr-Ti alloy.…”

Section: Resultsmentioning

confidence: 99%

Highly increased capacitance and thermal stability of anodic oxide films on oxygen-incorporated Zr-Ti alloy

Habazaki

Kobayashi

Tsuji

et al. 2017

J Solid State Electrochem

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Heat treatment of Zr-24 at% Ti alloy with barrier-type dielectric anodic oxide films was conducted at 473 K in air to examine the thermal stability of the dielectric oxide films for possible electrolytic capacitor application. The anodic oxide film was formed by anodizing of the alloy at 50 V for 30 min in 0.1 mol dm-3 ammonium pentaborate electrolyte. The anodic oxide film of 125 nm thickness was crystalline, containing both monoclinic and tetragonal ZrO 2 phase. It was found that marked thickening of the oxide film with generation of cracks occurred during heat treatment at 473 K. Thus, the dielectric loss was largely increased along with the capacitance increase. In contrast, the anodic oxide film formed on the oxygen-incorporated alloy remained uniform and no significant increase in dielectric loss was observed even after the heat treatment. The capacitance of the anodic film became as high as 4.8 mF m-2 , which was nearly twice that on Ta. The high capacitance was associated with the preferential formation of tetragonal ZrO 2 phase in the anodic oxide film on the oxygen-incorporated alloy. Findings indicated that the oxygen-incorporated Zr-Ti alloy is a promising novel material for capacitor application.

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Section: Resultsmentioning

confidence: 99%

Highly increased capacitance and thermal stability of anodic oxide films on oxygen-incorporated Zr-Ti alloy

Habazaki

Kobayashi

Tsuji

et al. 2017

J Solid State Electrochem

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“…Anodization was controlled using a DC power supply (Kepco BHK1000-0.2MG) with an output current of 0.3 mA. The target potential of the power supply was set to 85 V in order to obtain an ATO with a thickness of 135 nm (assuming an anodization rate of 1.6 nm/Volt 27,28 ). High surface area samples were produced by pressing 7.5 g of commercial tantalum powder with a capacitance-voltage per gram rating of 12000 uF · V/g to a press density of about 6 g/cm 3 .…”

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

In-Situ Stress Measurement during Heat Treatment of Amorphous Tantalum Oxide

Viste

Hossick-Schott

et al. 2015

ECS J. Solid State Sci. Technol.

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Heat treatment is known to improve the electrical and mechanical properties of amorphous tantalum oxide (ATO) in tantalum capacitor anodes. In-situ, multi-beam optical stress sensor (MOSS) measurements were performed on the ATO / tantalum system during heat-treatment in air and vacuum. Thermal desorption mass spectroscopy was also used to monitor species desorbing from the oxide during heating in vacuum. In addition, scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to characterize the heat-treated samples. The results suggest that the ATO/Ta system undergoes changes as a function of annealing temperature and atmosphere. At temperatures below ∼400 • C, the main effects are oxide dehydration and densification, indicated by a net compressive stress. After heat-treatment at temperatures above 400 • C in air, the net stress becomes increasingly compressive with increasing temperature. Oxide growth due to oxygen uptake is the likely cause for the compressive stress. In vacuum, the net stress remains tensile even after heat-treating at high temperatures above 400 • C. Dehydration and the formation of a high density of oxygen vacancies at the metal-oxide interface during heat-treatment are the likely causes for the net tensile stress-thickness. Tantalum capacitors are widely used in various electrical systems.1-3 Amorphous tantalum oxide (ATO) serves as the dielectric. The use of tantalum capacitors in high reliability applications generated intensive research on the electrical properties of the ATO, specifically on phenomena related to dielectric breakdown in high electric fields.3-7 Oxide defects such as interstitial oxygen ions and oxygen vacancies can significantly influence electrical and mechanical properties of ATO. [8][9][10] Heat treatment below the crystallization temperature of ATO is known to improve its electrical properties. 11-15However, some of the details of the oxide transformation and structural change of ATO during heat treating below its crystallization temperature remain unclear.14, [16][17][18][19][20] Temperature and atmosphere are the main parameters controlling the oxide transformation. Specifically, it is known that heating the as-grown, amorphous ATO to high temperatures around will result in the formation of crystallization oxide. 13,21,22 Phase transformations and reactions in solids are typically accompanied by volume changes that can induce stresses when the material is subjected to a mechanical constraint. In Ta capacitors, this occurs because the ATO dielectric is constrained by the underlying Ta metal. In-situ stress measurements have been previously employed to explore the details of phase transformations and reactions in thin solid films. 3,18,[23][24][25] In our recent work, this approach has been used to study the amorphous-to-crystalline phase transition in ATO under high electrical fields.3,26 For example, compressive stress of 0.06 GPa was generated in the ATO along with morphological changes that lead to cracking in the dielectric. 26 In the present stud...

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Reassessment of degradation mechanisms in anodic tantalum oxide capacitors under high electric fields

Cited by 2 publications

References 26 publications

Highly increased capacitance and thermal stability of anodic oxide films on oxygen-incorporated Zr-Ti alloy

Highly increased capacitance and thermal stability of anodic oxide films on oxygen-incorporated Zr-Ti alloy

In-Situ Stress Measurement during Heat Treatment of Amorphous Tantalum Oxide

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