Andrea Nannini

Electrochemical etching in HF solution for silicon micromachining

Abstract Electrochemical etching of silicon in hydrofluoric acid (HF) solution is employed as a micromachining technique. It is demonstrated that the commonly accepted geometric constraints on the shape of electrochemically etched silicon structures can be significantly relaxed. Several new structures etched on the same n-doped silicon wafer are reported. The fabricated structures include wall arrays, hole arrays, meander-shaped structures, spiral-like walls, microtubes, micropillars, microtips and more. A simple model for the electrochemical etch process, which describes the effect of the dimension of the initial seed, the current density, and also the KOH etching time of the initial pattern on the final geometries, is detailed.

APSFET: a new, porous silicon-based gas sensing device

In this paper, a new sensing device based on a FET structure having a PoSi layer as sensing material, namely adsorption porous silicon-based FET (APSFET), is proposed. The sensing mechanism is based on an gas-induced conduction channel in the crystalline silicon under the sensing layer, a new approach with respect to previously reported PoSi sensors. The fabrication process is based on a standard silicon process. In this work, the fabrication process along with an electrical characterization of the device in presence of different organic vapors (alcohols and acids) is presented and discussed.

Analysis, simulation and relative performances of two kinds of serpentine springs

A complete set of approximate, closed-form expressions, obtained with small displacements theory, for the spring constants of two kinds of serpentine springs (classic and rotated) is presented. The expressions are proposed as a tool for rapid design of microelectromechanical structures. The two designs are also studied numerically using the finite element method (FEM): analytical calculations and FEM simulations are compared. A comparison between the performances of the two designs is also briefly presented.

Dimensional Constraints on High Aspect Ratio Silicon Microstructures Fabricated by HF Photoelectrochemical Etching

The fabrication of macropores in crystalline silicon by photoelectrochemical etching in a hydrofluoric acid electrolyte is investigated. It is shown that the dimensional constraints on the pore diameters, which, in previous literature, are considered to depend on substrate doping, can be significantly relaxed. We show that it is possible to fabricate arrays of square section macropores with sides ranging from 2 to 15 mm using the same n-doped ~2.4-4 V cm! silicon substrate. Moreover, we demonstrate that macropore arrays with pitch variation up to 100% ~8 and 16 mm! can be simultaneously grown on the same silicon sample. The same process is used to fabricate arrays of silicon walls with different spacing and pitch as well. A simple model, based on the coalescence in a single pore of multiple stable pores, is proposed to explain the experimental data.

Gas and vapour effects on the resistance fluctuation spectra of conducting polymer thin-film resistors

The effects of various vapours on the power spectrum of the resistance fluctuation of polypyrrole thin-film resistors were studied. An ultra-low noise amplifier and current source were built in order to detect the very low signal and bias the resistors. The samples were obtained by means of chemical vapour deposition on to oxidizing precursors. The method was successfully extended to n-methylpyrrole and thiophene polymerization.

Current transport in free-standing porous silicon

The electrical conduction of free‐standing porous silicon layers, obtained from n+ silicon with various anodization currents and illumination conditions, has been investigated in vacuum as a function of the temperature in the interval 300‐210 K. The two‐contact I‐V characteristic is determined by the metal/porous silicon rectifying interface, whereas, by using the four‐contact technique, a linear dependence of the current vs voltage was found. The resistance of free‐standing samples showed a thermally activated behavior, with activation energies ranging from 0.1 to 0.44 eV. It was found that the activation energy decreased if the light intensity during the anodization was reduced. Variations of activation energy were also observed if the anodization current was changed but, in this case, it was not possible to find any correlation over the parameter range investigated.

Sensing properties of polypyrrole-polytetrafluoroethylene composite thin films from granular metal-polymer precursors

Abstract A newl class of sensor-oriented composite conducting thin films was grown utilizing an original method. The technique is based on the chemical polymerization of pyrrole (PY) vapours onto an oxidizing salt pattern obtained via chlorination of a co-sputtered granular metal thin film. Time stability of the samples realized with this technological approach and their response to exposure to different atmospheres were studied; the behaviour of the material subjected to mechanical strain was also investigated.

Vapour and gas sensing by noise measurements on polymeric balanced bridge microstructures

A procedure for depositing and patterning thin polypyrrole films is described. Geometrical resolution tests are presented showing that lines with submicrometric width can be produced by means of this technique. Noise measurements performed on balanced polypyrrole thin-film microbridges are presented. The measurements are aimed to study the effects of exposure to gaseous species on the spectral density of the resistance fluctuations. The use of balanced structures permits the effects of d.c. voltage transients and drift on the measured power spectra to be reduced.

Synthesis, structural characterization and electrical properties of highly conjugated soluble poly(furan)s

Abstract The polymerization of furan by different oxidants has been studied. Particular attention has been devoted to the nature of the reaction medium in combination with FeCl 3 as oxidizing agent. The use of a polar aprotic solvent with high donicity, such as propionitrile, allows one to obtain soluble oligo(furan)s with an ordered aromatic structure and hence high conjugation degree. These products, when blended with polar polymers such as poly(ethylene- co -vinyl acetate), give rise to films with good mechanical properties which, after I 2 -doping, display electrical conductivity of several orders of magnitude higher than that reported up to date for I 2 -doped powdery and intractable poly(furan)s.

Artificial sensing skin mimicking mechanoelectrical conversion properties of human dermis

Intrinsic mechanoelectrical conversion properties of skin tissues are investigated, and their origin is suggested to originate primarily from electrokinetic phenomena (streaming potentials) operating in the dermis. Human dermis is considered in analogy to other connective tissue as a biphasic, composite material in which the extracellular fluid permeates a negatively charged gel-like matrix of glycoproteins. A synthetic analog implementing a mechanoelectrical transduction mechanism thought to operate in dermis is realized. A biomorphic tactile sensor is devised and its dynamic transduction response is theoretically and experimentally analyzed. The streaming potential artificial skin appears to be particularly suited for applications in which ideal mechanical matching with body tissues or soft touch grasp are required.<<ETX>>