Thermal degradation of anodic niobia on niobium and oxygen-containing niobium

Abstract

Thermal treatment of anodized niobium and oxygen-containing niobium has been carried out to elucidate the thermal degradation mechanism of niobium capacitors and to clarify the influence of oxygen dissolved in niobium on thermal degradation. The capacitance and leakage current of the anodized specimens increase with thermal treatment above 423 K in air, although the oxygen content in the substrate has no significant effect up to 523 K. At increased temperatures, the changes in capacitance and leakage current are suppressed with increasing oxygen content. The anodic film formed on the Nb-50 at% O substrate thickens significantly during thermal treatment at 623 K in air, while only a slight reduction of the thickness is evident for those on the niobium and Nb-20 at% O substrates. In contrast, vacuum thermal treatment at 623 K causes thinning of the anodic film on niobium, with evidently no change in the film thickness on the Nb-50 at% O substrate. These are interpreted in terms of oxygen diffusion from the anodic film to the substrate as well as thermal oxide growth.

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

“…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.…”

“…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. As reported in liter ature [26,27, and, Refs. therein] some oxygen dissolu tion into the underlying niobium metal occurred dur ing the annealing.…”

“…11 we report the fitted capacitance vs. potential plots according to the theory of a SC Schot tky barrier for the same frequencies previously used in M-S analysis. The fitting parameters at the different frequencies are those reported in the caption but a more detailed study of the fitting process can be found in a previous work [19,26]. By a trial and error proce dure and by imposing the constraints on the flat band potential (U fb constant at any frequency for which ψ C ≥ 3k В Т/|е|) and on ψ C : (19) (see Eq.…”

“…More detailed information both on the spatial and energy dependence of electronic DOS of a SC can be derived by fitting the admittance vs. potential plots at different frequencies as discussed in several older C SC 2 -papers for anodic niobia and anodic tungsten oxide electrodes [4,[16][17][18] and more recently for thermally aged niobia grown on sputtered metal [26]. According to the theory [16,26], owing to the more spectroscopic character of the conductance, originating in a very narrow region of the barrier around х С , it is possible from the curves plotted in Fig.…”

“…According to the theory [16,26], owing to the more spectroscopic character of the conductance, originating in a very narrow region of the barrier around х С , it is possible from the curves plotted in Fig. 12 to derive the spatial distribution of the DOS at the energy level (E F -|e|ψ C ) (fixed frequency) as a function of the distance from the metal/oxide interface.…”