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

Abstract

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 (10−4–104 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.

The planar anodic Al 2 O 3 -ZrO 2 nanocomposite capacitor dielectrics for advanced passive device integration

“…Immediately following the anodizing, the re-anodizing was carried out via a high-speed potentiodynamic polarization (10 V·s −1 ) to a higher voltage selected from a range of 80–320 V. Upon attaining the desired voltage value, the voltage was stabilized for 5 min to ensure uniform oxide growth across the whole sample surface. This combination of electrical and electrolytic conditions for processing the Al/Zr bilayer was justified in the previous work [ 27 ]. The samples were then thoroughly washed with Milli-Q® ultrapure water, dried in a cool nitrogen stream, and placed in an oven preheated to 393 K for 1 h to fully desorb the moisture from the alumina nanopores.…”

“…Typically, the PAA-assisted anodic-oxide nanostructures are deep-located inside the pores, such that the upper volume of pores remains free from the underlying metal oxide [ 35 ]. Some deep-located oxides (Ta 2 O 5 [ 39 ], HfO 2 [ 40 ], and ZrO 2 [ 27 ]) behave as nearly ideal dielectrics when measured by electrochemical impedance spectroscopy in solution. Such PAA-inbuilt films are advantageous for electrolytic capacitors as the empty pores above the oxide nanocolumns serve as a spacer and collector for a liquid or gel-like electrolyte [ 27 , 40 ].…”

“…Some deep-located oxides (Ta 2 O 5 [ 39 ], HfO 2 [ 40 ], and ZrO 2 [ 27 ]) behave as nearly ideal dielectrics when measured by electrochemical impedance spectroscopy in solution. Such PAA-inbuilt films are advantageous for electrolytic capacitors as the empty pores above the oxide nanocolumns serve as a spacer and collector for a liquid or gel-like electrolyte [ 27 , 40 ]. However, a planar non-porous anodic oxide film is required for MIM capacitor fabrication.…”

“…For the first time, the films have been integrated as the high- k nanocomposite dielectric in on-chip MIM microdevices. The choice of material was motivated by the generally attractive dielectric properties of both ZrO 2 and Al 2 O 3 , complemented by the enhanced properties of the Al 2 O 3 –ZrO 2 dielectrics utilized in an experimental electrolytic capacitor design [ 27 ]. The anodic films and test MIM devices have been examined by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray microdiffraction (XRD), electrochemical impedance spectroscopy, and electrical/dielectric measurements in a frequency range of 10 −2 –10 6 Hz at temperatures ranging 293–523 K. An array of integral capacitors utilizing the new dielectrics has been modeled in pursuit of creating the missing technology to complement the anodizing conception of passive device integration for PEDs.…”

Anodizing of Hydrogenated Titanium and Zirconium Films

“…Anodic oxide films of aluminum (Al) and other valve metals (Ta, Nb, Ti, Hf, Zr, and W) are promising materials for electronic technology [1][2][3][4][5][6]; therefore, electrochemical behavior was investigated [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]. At the same time, under certain conditions, all these metals (Al [22], Ta [23], Nb [24], Ti [25], Hf [26], Zr [27], W [28], and others [29]) absorb significant amounts of hydrogen, and the volume of the absorbed hydrogen is several orders of magnitude larger than the volume of the metal.…”