The planar anodic Al2O3-ZrO2 nanocomposite capacitor dielectrics for advanced passive device integration.

The need for integrated passive devices (IPDs) emerges from the increasing consumer demand for electronic product miniaturization. Metal-insulator-metal (MIM) capacitors are vital components of IPD systems. Developing new materials and technologies is essential for advancing capacitor characteristics and co-integrating with other electronic passives. Here we present an innovative electrochemical technology joined with the sputter-deposition of Al and Zr layers to synthesize novel planar nanocomposite metal-oxide dielectrics consisting of ZrO2 nanorods self-embedded into the nanoporous Al2O3 matrix such that its pores are entirely filled with zirconium oxide. The technology is utilized in MIM capacitors characterized by modern surface and interface analysis techniques and electrical measurements. In the 95-480 nm thickness range, the best-achieved MIM device characteristics are the one-layer capacitance density of 112 nF·cm-2, the loss tangent of 4·10-3 at frequencies up to 1 MHz, the leakage current density of 40 pA·cm-2, the breakdown field strength of up to 10 MV·cm-1, the energy density of 100 J·cm-3, the quadratic voltage coefficient of capacitance of 4 ppm·V-2, and the temperature coefficient of capacitance of 480 ppm·K-1 at 293-423 K at 1 MHz. The outstanding performance, stability, and tunable capacitors' characteristics allow for their application in low-pass filters, coupling/decoupling/bypass circuits, RC oscillators, energy-storage devices, ultrafast charge/discharge units, or high-precision analog-to-digital converters. The capacitor technology based on the non-porous planar anodic-oxide dielectrics complements the electrochemical conception of IPDs that combined, until now, the anodized aluminum interconnection, microresistors, and microinductors, all co-related in one system for use in portable electronic devices.

Anodic formation and biomedical properties of hafnium-oxide nanofilms.

Hafnium dioxide (HfO2) is attracting attention for bio-related applications due to its good cytocompatibility, high density, and resistance to corrosion and mechanical damage. Here we synthesize two types of hafnium-oxide thin films on substrates via self-organized electrochemical anodization: (1) an array of hierarchically structured nanorods anchored to a thin oxide layer and (2) a microscopically flat oxide film. The nanostructured film is composed of a unique mixture of HfO2, suboxide Hf2O3, and oxide-hydroxide compound HfO2·nH2O whereas the flat film is mainly HfO2. In vitro interaction of the two films with MG-63 osteoblast-like cells and Gram-negative E. coli bacteria is studied for the first time to assess the potential of the films for biomedical application. Both films reveal good cytocompatibility and affinity for proteins, represented by fibronectin and especially albumin, which is absorbed in a nine times larger amount. The morphology and specific surface chemistry of the nanostructured film cause a two-fold enhanced antibacterial effect, better cell attachment, significantly improved proliferation of cells, five-fold rise in the cellular Young's modulus, slightly stronger production of reactive oxygen species, and formation of cell clusters. Compared with the flat film, the nanostructured one features the weakening of AFM-measured adhesion force at the cell/surface interface, probably caused by partially lifting the nanorods from the substrate due to the strong contact with cells. The present findings deepen the understanding of biological processes at the living cell/metal-oxide interface, underlying the role of surface chemistry and the impact of nanostructuring at the nanoscale.

Tuning the response of osteoblast-like cells to the porous-alumina-assisted mixed-oxide nano-mound arrays.

Nanostructuring of biomaterials is used to create an appropriate interfacial layer that promotes stable cellular adhesion, proliferation, and differentiation on orthopedic and dental implants. Here, we synthesize self-organized arrays of composite-oxide nano-mounds through anodizing Al/Ta bilayers sputtered on substrates to cover the "missing" smallest size range of 10-40 nm for structuring an advanced inorganic biomaterial-Al2 O3 -doped Ta2 O5 films. The osteoblast-like cells appear to be able to recognize the finest differences in the film nano-morphologies. In the absence of serum proteins, the adhesion and cell growth are substantially enhanced on the 20 and 40 nm nanoarrays while in complete medium the cells show better initial adhesion on the 10 nm nanoarrays. The proliferation assay reveals a significant rise in cell number on the 20 and 40 nm nanoarrays during the first 7 days. A remarkable increase in the alkaline phosphatase activity is noticed on the 40 nm nanoarray. Immunostaining of cells adhered to the nano-mound surfaces shows that the cells are well spread over all the nanostructured films with organized actin fibers. The larger surface areas and improved focal contacts are again associated with the 20 and 40 nm nanoarrays. The findings help improve compatibility of living cells with the metal-oxide nanostructured surfaces developed for tissue engineering. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1645-1654, 2018.

Multifrequency interrogation of nanostructured gas sensor arrays: a tool for analyzing response kinetics.

This paper presents a unique perspective on enhancing the physicochemical mechanisms of two distinct highly sensitive nanostructured metal oxide micro hot plate gas sensors by utilizing an innovative multifrequency interrogation method. The two types of sensors evaluated here employ an identical silicon transducer geometry but with a different morphological structure of the sensitive film. While the first sensing film consists of self-ordered tungsten oxide nanodots, limiting the response kinetics of the sensor-chemical species pair only to the reaction phenomena occurring at the sensitive film surface, the second modality is a three-dimensional array of tungsten oxide nanotubes, which in turn involves both the diffusion and adsorption of the gas during its reaction kinetics with the sensitive film itself. By utilizing the proposed multifrequency interrogation methodology, we demonstrate that the optimal temperature modulation frequencies employed for the nanotubes-based sensors to selectively detect hydrogen, carbon monoxide, ethanol, and dimethyl methyl phosphonate (DMMP) are significantly higher than those utilized for the nanodot-based sensors. This finding helps understand better the amelioration in selectivity that temperature modulation of metal oxides brings about, and, most importantly, it sets the grounds for the nanoengineering of gas-sensitive films to better exploit their practical usage.