A Rutherford Backscattering Analysis of Anodic Tantalum‐Titanium Oxides

Abstract

Sputtered tantalum‐titanium alloy thin films have been anodized in 0.01% aqueous citric acid, and the atom distribution, stoichiometry, and thickness determined by Rutherford backscattering analysis and stylus measurement. The anodic oxide film consists of a uniform amorphous mixture of Ta2O5 and TiO2 with about 3% of the oxide at the electrolyte interface consisting of almost pure TiO2 . During anodization a small fraction of the titanium dissolves in the electrolyte. The apparent growth constant of the anodic oxide on Ta0.49Ti0.51 films is 1.88±0.02 normalnm/V . The density of the oxide is determined as false(5.9±0.2false)×103 normalkg/m3 . From aqueous contact capacitance measurements, the dielectric constant of the alloy anodic oxide is 24.7±0.9 .

Dielectric and mechanical properties of anodic films in the Ta–Ti system

“…The occurrence of two-layered films on Ta-Ti alloys, agreeing with an earlier study of a relatively concentrated alloy, 12 is typical of anodizing alloys when one of the cation species migrates more rapidly than the other through the film. 21 Similar to the present case, the more mobile species is usually associated with the lower single metal-oxygen bond energy; the respective values for Ti 4C -O and Ta 5C -O bonds are 319 and 347 kJ mol 1 .…”

“…6,26 The values for the present alloy films determined by TEM are in the approximate range 1.6-1.9 nm V 1 , which is consistent with previous observations of intermediate ratios for binary anodic oxides. 27 Previous work using RBS on alloys containing ¾50 at.% Ti reported a formation ratio of 1.88 nm V 1 for films grown in citric acid solution, 12 similar to the ratio found here for the Ta-40 at.% Ti alloy. The thickness of the titania layer was estimated as being 3% of the film thickness, 12 which is less than the relative thickness of ¾7% found by TEM for the latter alloy.…”

“…27 Previous work using RBS on alloys containing ¾50 at.% Ti reported a formation ratio of 1.88 nm V 1 for films grown in citric acid solution, 12 similar to the ratio found here for the Ta-40 at.% Ti alloy. The thickness of the titania layer was estimated as being 3% of the film thickness, 12 which is less than the relative thickness of ¾7% found by TEM for the latter alloy.…”

Influence of silicon on the growth of barrier-type anodic films on titanium

“…In growing anodic films with an amorphous structure on a range of valve metals, including aluminium [16], niobium [17], tantalum [18][19][20] and titanium [8,9], silicon species are known to be immobile. Thus, transport numbers of cations and anions during film growth can be determined from the distribution of silicon species, which act as marker species.…”

Growth and field crystallization of anodic films on Ta–Nb alloys

“…The change in band gap energy of "mixed oxide" with composition is also of fundamental interest [22]. Anodizing of tantalum alloys has been investigated for improving the dielectric properties of anodic Ta 2 O 5 , which is extensively used as a dielectric in the capacitor industry, as well as for increased understanding of the growth mechanism of anodic oxides [23][24][25][26][27][28][29][30][31]. Anodic Nb 2 O 5 formed on niobium is also a promising dielectric for capacitor applications due to the high dielectric constant (ε ox =42) compared with anodic Ta 2 O 5 (ε ox =27) [32,33].…”