Anodic aluminum oxide processing, characterization and application to DNA hybridization electrical detection

Metal oxides have recently come under study thanks to their physical and electrical properties for different applications such as MOS devices, i.e. substituting the silicon oxide with a high-k material, or as MIM (Metal Insulator Metal) capacitors, to increase capacitance per unit area and circuit integration. One oxide of interest in this field is aluminum oxide since it features good electrical insulation and high dielectric constant. In-depth studies are presented here on the use of non-porous anodic Al2O3. Major physical and electrical parameters have been obtained, i.e. dielectric constant, stress, deformation, resistance, surface quality. Constant, low anodizing current density results in a denser oxide, with a thickness of around 100 nm. Performances such as capacitance, breakdown voltage, etc. can be improved when compared to other Al2O3 obtained by other methods. Results are also comparable to other high-k oxides. Fair performance is maintained for temperature raised up to 200°C, which opens new possible applications. Its mechanical and physical properties make it candidate in biological and MEMS devices. DNA re-association or hybridization is the underlining principle of DNA sensors. Different electrical Al structures protected by a thin anodic Al2O3 are tested. Interdigitated capacitors, the most promising electrical structure, were selected and process characterization performed. Three electrical extraction procedures are performed on the same device lying on a passivated silicon substrate: inter-electrodes capacitance, the self-resonance frequency, and the equivalent MOS capacitance between the short-circuited electrodes and the substrate. This study is the first of its kind to open the way for correlation studies and noise reduction techniques based on multiple electrical measurements of the same DNA hybridization event. The hybridization of concentrations as low as 50 pM target DNA has been successfully electrically detected using silver enhancement over gold nano-particles labeled DNA.