Preparation of Tantalum Anodic Oxide Film in Citric Acid Solution - Evidence and Effects of Citrate Anion Incorporation

Abstract

ABSTRACT:Tantalum anodic oxide film was prepared in citric acid solution of various concentrations and the prepared Ta anodic oxide film was characterized by various electrochemical techniques and X-ray photoelectron spectroscopy (XPS). The prepared Ta anodic oxide film showed typical n-type semiconducting properties and the dielectric properties were strongly dependent on the citric acid concentration. The variation of electrochemical and electronic properties was explained in terms of electrolyte anion incorporation into the anodic oxide film, which was supported by XPS measurements.

Ultra-thin anodized aluminium dielectric films: the effect of citric acid concentration and low-voltage electronic applications

“…The analysis of the recorded spectra confirms that there is virtually no difference in the composition of both types of films. No traces of carbon in the anodized films of aluminium presented here is in strong contrast to the citric acid anodized tantalum films reported previously where incorporation of citric acid anion was observed (20). It is also crucial to note here that the peaks appeared on EDS spectra for the elements sodium (Na), calcium (Ca), and silicon (Si) originates from the used glass substrates.…”

“…It is shown that the chemical structure, surface morphology and the dielectric properties of the Al2O3 layers are not affected by the variation of citric acid concentrations from 0.1 to 1000 mM. This finding is in a strong contrast with the recently reported anodized aluminium and tantalum films where it was shown that electrolyte byproducts are incorporated into barrier-type anodic coatings (20,21). The chemical composition and stoichiometry of the anodized Al films are studied using EDS and XPS, respectively.…”

Low-Voltage Electrowetting on Dielectrics Integrated and Investigated with Electrical Impedance Spectroscopy (LV-EWOD-EIS)

“…The slope of the linear fitting yields a layer growth coefficient of (1.94 ± 0.05) nm/V. This value is comparable with the result reported by Kim et al 75 for a 22-nm-thick anodic Ta 2 O 5 layer prepared in a citric acid solution at 10 V. In comparison with the Ta 2 O 5 layers anodized at higher voltages (30 -50 V), the Ta 2 O 5 layer anodized at the lowest voltage (20 V) shows an outlier behavior concerning its thickness (Figure 4.5). On one hand, its mean value deviates most from the linear dependence of the layer thickness on the voltage.…”

“…A promising material for the main dielectric layer is anodic tantalum pentoxide (Ta 2 O 5 ). Its relative permittivity (* $ = 25.3 -29.5) [74][75][76][77] is much higher in comparison with the commonly used dielectrics, such as silicon oxide (* $ = 3.9) [78][79] and silicon nitride (* $ = 7.5) 73 . Besides its high relative permittivity, Ta 2 O 5 features high breakdown strength (4 -6.61 MV/cm) 76,[80][81] and low pin-hole density 70,82 .…”

“…However, most of the techniques require expensive equipment with vacuum condition or high temperature to obtain a low-defect smooth oxide layer. In comparison, anodic oxidation (anodization) 75,[89][90] is a low-cost and promising fabrication method: anodic Ta 2 O 5 thin layers can possess a higher film density (8.01 g/cm 3 ) 90 than those obtained with other preparation methods 83 , higher relative permittivity (values listed above) and better layer quality (e.g. negligible pin-holes) 70 than those produced by sputtering (* $ = 20 -23) 71,91 .…”