We demonstrate patterned Al2O3 formation by post-plasma oxidation of a thin layer of aluminium (Al) film deposited by electron beam evaporator in area selective regions. The oxide quality is observed to further improve by annealing in O-2 and N-2 environment. Schottky and metal-insulator-semiconductor diodes are also fabricated to characterize its electrical behaviour. The thickness and high quality of the oxide formed is confirmed from Transmission Electron Microscope (TEM) and X-Ray Photoelectron Spectroscopy (XPS) analysis. The O-2 and N-2 annealed samples show Oxygen to Aluminium atomic ratio of similar to 1.5 confirming near-ideal stoichiometry. The energy band-gap (E-g) of the Plasma-Oxide, O-2-Annealed and N-2-Annealed estimated from energy loss spectra of O-1s are found to be 5.0, 5.5 and 6.8 eV, respectively. The valance band off-set for the corresponding oxides as estimated from low energy spectra analysis are found to be 0.8, 0.7 and 0.8 eV, respectively. The electrical characteristics also confirm improvement over the control device. The ION/IOFF ratios are observed to be 10(6), 10(10) and 10(6) for the Plasma Oxide, O-2 Annealed and N-2 Annealed oxides, respectively, as compared to 10(3) for the Control sample. The dielectric constants (epsilon(ox)) for the corresponding oxides as determined from the C-V characteristics are found to be 5.3, 8.5 and 8.7, respectively.