Doctoral Thesis

Dielectric Properties of Thin Tantalum and Niobium Oxide Layers

Text 3.21 MB Appendix 11.57 kB Thesis 2.08 MB

Author of thesis: Ing. Inas Faisel Abuetwirat, Ph.D.

Acad. year: 2014/2015

Supervisor: doc. Ing. Karel Liedermann, CSc.

Reviewer's: prof. RNDr. Zdeněk Chobola, CSc., doc. Ing. Jaroslav Lelák, CSc.

Abstract:

Dielectric relaxation spectroscopy is one of the useful methods in studying the molecular dynamics of materials. Owing to recent developments in instrumentation and advances in measurement technique, it is possible to obtain the dispersion of dielectric permittivity in a wide frequency range and for very different materials.

The purpose of my work was to investigate dielectric relaxation spectra and conductivity of oxides of titanium, niobium, tantalum, lanthanum and hafnium for field emission cathodes. The objective of the research was to analyze the frequency and temperature behavior of these oxides, as well as their conductivity over a wide frequency and temperature range, and to attempt to determine the origin of the relaxation. As the original range of oxides has been very broad, focus was paid to tantalum (Ta) and niobium (Nb) oxides only, also with regard to their application in electrolytic capacitors.

Electrical, thermal and mechanical (processing) properties of Ta and Nb oxides have already been well established. Little is known, however, about detailed mechanisms of their dielectric relaxation.

The results acquired for Ta2O5 show a relaxation peak in the temperature and frequency range available, 187 K – 385 K, 1 Hz – 10 MHz. The loss peak frequency follows the Arrhenius law dependence with the activation energy of 0.048 eV. In conductivity spectra, Ta2O5 film exhibits a steady – state value at low frequencies and a monotonous increase at high frequencies that depends on temperature. The observed conductivity followed a slightly superlinear power law. The results acquired for Nb2O5 show a relaxation peak in a similar temperature and frequency range, 218 K – 373 K, 1 Hz – 1 MHz. The loss peak frequency follows the Arrhenius law dependence with the activation energy of 0.055 eV. For both films the relaxation peak approximately shifted toward higher temperatures with frequency (same activation energy). Niobium capacitor shows conductivity mechanism similar to tantalum capacitor.

Keywords:

Dielectric spectroscopy, dielectric relaxation, dielectric spectra, electrical conductivity, tantalum oxide, niobium oxide.

Date of defence

17.12.2014

Result of the defence

Defended (thesis was successfully defended)

znakmkaPznamka

Process of defence

Předložená disertační práce se věnuje aktuálnímu tématu – studiu dielektrických vlastností tenkých vrstev tantalu a oxidu niobu vhodných pro elektrolytické kondenzátory. Doktorandka prezentovala současný stav problematiky dielektrické relaxační spektroskopie, cíle práce a zejména vlastní přínos ke studovanému tématu. Doktorandka zodpověděla v rozpravě řadu dotazů týkajících se navržené metodiky a směrů dalšího výzkumu kvalitních tenkých vrstev pro elektrolytické kondenzátory. Komise konstatovala, že obhajoba proběhla úspěšně, a že výsledky disertace by mohly být přínosné pro další rozvoj oboru.

Language of thesis

English

Faculty

Department

Study field

Physical Electronics and Nanotechnology (PK-FEN)

Composition of Committee

prof. RNDr. Pavel Tománek, CSc. (předseda)
prof. RNDr. Vladimír Aubrecht, CSc. (člen)
prof. Ing. RNDr. Josef Šikula, DrSc. (člen)
doc. RNDr. Pavel Moravec, CSc. (člen)
prof. Ing. Karel Hájek, CSc. (člen)
Ing. Petr Jákl, Ph.D. (člen)
doc. Ing. Jaroslav Lelák, CSc. - oponent (člen)
prof. RNDr. Zdeněk Chobola, CSc. - oponent (člen)

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