The Heat-Treatment of Anodic Oxide Films on Tantalum

Abstract

Dielectric measurements have been made on tantalum which has been anodically oxidized in aqueous phosphoric acid of various concentrations and then heated in air. The resulting dielectric consists of a highly conducting portion adjacent to the tantalum and an outer, nonconducting portion. This structure is interpreted in terms of the distribution of phosphorus incorporated into the oxide and its effect on the diffusion of oxygen during heat‐treatment.

Mechanism of formation and growth of sunflower-shaped imperfections in anodic oxide films on niobium

“…Therefore, if niobium capacitors are used, the size could be smaller than that of tantalum capacitors for the same performance. However, anodic oxide films on niobium have dielectric properties that are unsuitable for capacitors: (i) there are increases in capacitance and leakage current by heat treatment [2][3][4][5][6][7][8][9][10][11][12], and (ii) there is a bias voltage dependence of the capacitance [11][12][13][14][15][16][17][18]. A previous investigation reported that these properties are caused by imperfections in the anodic oxide films, which are grown by heat treatment [10] or by potentiostatic anodizing [13].…”

Anodically formed oxide films on niobium: Microstructural and electrical properties

“…34,35 This analysis resulted in calculated donor densities ranging from 8 × 10 18 /cm 3 for as-anodized samples to 2 × 10 18 /cm 3 for oxidized and annealed samples. 36 The described electrical response of as-anodized and annealed niobium anode capacitor samples is in contrast with the early work of Smyth et al 20,[37][38][39][40] who examined the effect of elevated temperatures on the electrical performance of the Ta/Ta 2 O 5 -and Nb/Nb 2 O 5 -systems in detail. During their comprehensive studies they were able to demonstrate that the temperature dependence of the capacitance of as-formed Nb 2 O 5 films is much higher than for the comparable tantalum case.…”

“…Since the specific conductivity of 18 wt% H 2 SO 4 is significant high, any influence of the measuring electrolyte conductivity on capacitance measurements can be excluded. 20 The measurements were performed at f = 120 Hz with bias voltages ranging from−0.5 V to 15 V. All measured capacitances C meas. were transformed into specific charge values Q according to Q = C meas ·U ox .…”

“…One possible explanation of these contrary results might be due to thermally induced physical damage within the samples investigated by Smyth et al since in ref. [20] it was mentioned that physical damage might be localized at the edge of the samples. Moreover, capacitor-grade niobium powders were not available that time.…”

“…[15][16][17][18][19] One drawback of Nb-based capacitors which is often referred to in the literature is the pronounced temperature sensitivity of the Nb 2 O 5 film. [20][21][22][23] Since the fabrication process of solid electrolyte capacitors with MnO 2 cathode comprises several production steps at elevated temperatures, the comprehensive understanding of the influence of heat treatments on the electrical properties of nanoscale Nb 2 O 5 layers on niobium is essential.…”