The Growth, Composition, and Functional Properties of Self-Organized Nanostructured ZrO2-Al2O3 Anodic Films for Advanced Dielectric Applications

An aluminum-on-zirconium bilayer is anodized in oxalic acid solution to transform the Al layer into porous anodic alumina (PAA); this is followed by the PAA-assisted re-anodizing of the Zr underlayer at voltages 40-280 V. The process results in an array of amorphous ZrO2 nanocolumns, 45-330 nm long, partly filling the PAA pores and anchored to a continuous bottom oxide layer under the pores, 20-130 nm thick, comprising a ZrO1.8 spongelike sublayer superimposed on a ZrO1.5 compact sublayer. The thicknesses of the nanostructured and bottom oxides increase linearly with re-anodizing voltage, disclosing a low film formation ratio of 1.65 nm V-1, which is impossible with anodic ZrO2. The amorphous ZrO2 nanocolumns embedded in the highly resistive amorphous PAA matrix combined with the laminated bottom oxide reveal a nearly ideal dielectric performance in a wide frequency range (10(-4)-10(4) Hz) complemented by the low leakage currents and high breakdown voltages (up to 280 V). The film permittivity may be tuned, from 11 to 20, by combining the anodizing and pore-widening techniques. The advantageous architecture, fabrication approach, and functional properties of the films allow the design of a prototype of an emerging hybrid polymer electrolytic microcapacitor for on-chip integration.