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

Abstract

Anodically oxidized, ultra-thin (d < 10 nm) aluminium films emerge as the dielectric of choice for low-cost thin film capacitors (TFCs), thin film transistors (TFTs), and bio- and chemical sensors. In this work, the dielectric properties of ultra-thin aluminium oxide films grown by anodization in aqueous solutions of citric acid (CA) have been studied. It is observed that the electrolyte strength variation from 0.1 mM to 1000 mM has virtually no influence on the chemical composition, surface morphology and the dielectric properties of the fabricated alumina films. The anodized films are very smooth having RMS area roughness around ∼5 Å. This was further improved after deposition of n-octadecyltrichlorosilane (OTS) self-assembled monolayer (SAM) to ∼4 Å. Also, the XRD and elemental analysis using EDS and XPS unambiguously confirms that the obtained oxide films are amorphous, stoichiometric Al2O3 without any carbon contamination. The fabricated Al/Al2O3/Al MIM capacitors show almost ideal capacitor characteristics from 10 Hz to 100 kHz. It has been found that the OTS coating does not only improve the capacitor frequency response further but also reduces the leakage current through the dielectric layer by passivating reactive dangling bonds on the oxide surface. As a result of the favourable properties of the anodized Al2O3/OTS films, high-performance, low threshold voltage organic thin film transistors (OTFTs) operating below 1 V are successfully demonstrated.