Internal stress evolution during field-induced crystallization of anodic tantalum oxide

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

doi:10.1016/j.electacta.2012.07.035

Cited by 15 publications

(20 citation statements)

References 18 publications

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“…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 . Subsequently, the samples were sintered at 1550…”

Section: Methodsmentioning

confidence: 99%

“…3,26 The same technique has been used here to study internal stresses generated in ATO films during the annealing. Here, this approach is implemented in a high temperature vacuum system.…”

Section: Methodsmentioning

confidence: 99%

“…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 study, this approach is used to examine stress evolution in the ATO during heat treatments.…”

mentioning

confidence: 99%

“…[1][2][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.…”

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confidence: 99%

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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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Section: Methodsmentioning

confidence: 99%

“…3,26 The same technique has been used here to study internal stresses generated in ATO films during the annealing. Here, this approach is implemented in a high temperature vacuum system.…”

Section: Methodsmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

See 2 more Smart Citations

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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“…The amorphous tantalum oxide (ATO) formed electrochemically is the dielectric layer in these capacitors [1][2][3][4][5][6][7][8]. The degradation of ATO's dielectric properties upon prolonged exposure to high electric field stress has been the focus of a large number of prior investigations [1,3,5,[9][10][11][12][13][14][15][16][17].…”

Section: Introductionmentioning

confidence: 99%

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

Viste

Hossick-Schott

et al. 2014

J Mater Sci

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High-voltage Ta capacitors have broad applications in various electric systems. Anodically grown, amorphous tantalum oxide (ATO) serves as the dielectric in these capacitors. A detailed understanding of the behavior of ATO exposed to high electric fields is highly desirable and is reflected in a number of prior investigations into this subject. In the conventional view, the electric field promotes the growth of crystalline oxide, which is electrically more conductive and thus leads to the degradation of the dielectric. This interpretation is re-examined using several advanced characterization techniques. The results indicate that oxidation of the ATO and underlying Ta occurs preferentially at specific locations. Subsequent crystallization at these sites was only observed in specimens where this enhanced oxidation led to cracking in the ATO. The results with different Ta materials indicate that these cracks are more prevalent with rougher surfaces. The reported sequence of mechanisms that leads to crystallization provides new insight that can potentially be employed to improve the reliability and stability of Ta capacitors.

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Major Degradation Mechanisms

Freeman¹

2021

Tantalum and Niobium-Based Capacitors

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Internal stress evolution during field-induced crystallization of anodic tantalum oxide

Cited by 15 publications

References 18 publications

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

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

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

Major Degradation Mechanisms

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