Denis Perrone

Silver nanoparticle ink technology: state of the art

Printed electronics will bring to the consumer level great breakthroughs and unique products in the near future, shifting the usual paradigm of electronic devices and circuit boards from hard boxes and rigid sheets into flexible thin layers and bringing disposable electronics, smart tags, and so on. The most promising tool to achieve the target depends upon the availability of nanotechnology-based functional inks. A certain delay in the innovation-transfer process to the market is now being observed. Nevertheless, the most widely diffused product, settled technology, and the highest sales volumes are related to the silver nanoparticle-based ink market, representing the best example of commercial nanotechnology today. This is a compact review on synthesis routes, main properties, and practical applications.

Evaluation of different PDMS interconnection solutions for silicon, Pyrex and COC microfluidic chips

One of the most crucial issues in the domain of microfluidics is the chip to world interface. This paper describes a characterization methodology of a quite common microfluidic interconnection scheme, based on polydimethylsiloxane (PDMS), applied to some of the most popular substrates (silicon, Pyrex and cyclic olefin copolymer) for microfluidic applications. Particular emphasis is given to the evaluation of leakage endurance as a function of the main geometrical parameters of the interconnections and the selected bonding technique. Oxygen plasma activation of the PDMS surface and the application of a thin PDMS interlayer demonstrated the most attractive solutions, due to the straightforward approach and limited cost. Maximum sustainable pressures in excess of 200 kPa have been achieved. Results obtained are critically discussed with the aim to outline PDMS interconnection guidelines for different microfluidic applications.

A multilevel Lab on chip platform for DNA analysis

Lab-on-chips (LOCs) are critical systems that have been introduced to speed up and reduce the cost of traditional, laborious and extensive analyses in biological and biomedical fields. These ambitious and challenging issues ask for multi-disciplinary competences that range from engineering to biology. Starting from the aim to integrate microarray technology and microfluidic devices, a complex multilevel analysis platform has been designed, fabricated and tested (All rights reserved—IT Patent number TO2009A000915). This LOC successfully manages to interface microfluidic channels with standard DNA microarray glass slides, in order to implement a complete biological protocol. Typical Micro Electro Mechanical Systems (MEMS) materials and process technologies were employed. A silicon/glass microfluidic chip and a Polydimethylsiloxane (PDMS) reaction chamber were fabricated and interfaced with a standard microarray glass slide. In order to have a high disposable system all micro-elements were passive and an external apparatus provided fluidic driving and thermal control. The major microfluidic and handling problems were investigated and innovative solutions were found. Finally, an entirely automated DNA hybridization protocol was successfully tested with a significant reduction in analysis time and reagent consumption with respect to a conventional protocol.

Synthesis of polyaniline-based inks for inkjet printed devices: Electrical characterization highlighting the effect of primary and secondary doping

Engineering applications for printed electronics demand solution processable electrically conductive materials, in the form of inks, to realize interconnections, piezoresistive pressure sensors, thermoresistive temperature sensors, and many other devices. Polyaniline is an intrinsically conductive polymer with modest electrical properties but clear advantages in terms of solubility and stability with temperature and in time. A comprehensive study, starting from its synthesis, primary doping, inkjet printing and secondary doping is presented, with the aim of elucidating the doping agent effects on its morphology, printability and electronic performance.

pH-triggered conduction of amine-functionalized single ZnO wire integrated on a customized nanogap electronic platform

The electrical conductance response of single ZnO microwire functionalized with amine-groups was tested upon an acid pH variation of a solution environment after integration on a customized gold electrode array chip. ZnO microwires were easily synthesized by hydrothermal route and chemically functionalized with aminopropyl groups. Single wires were deposited from the solution and then oriented through dielectrophoresis across eight nanogap gold electrodes on a platform single chip. Therefore, eight functionalized ZnO microwire-gold junctions were formed at the same time, and being integrated on an ad hoc electronic platform, they were ready for testing without any further treatment. Experimental and simulation studies confirmed the high pH-responsive behavior of the amine-modified ZnO-gold junctions, obtaining in a simple and reproducible way a ready-to-use device for pH detection in the acidic range. We also compared this performance to bare ZnO wires on the same electronic platform, showing the superiority in pH response of the amine-functionalized material.

Development of a Flexible Lead-Free Piezoelectric Transducer for Health Monitoring in the Space Environment

In this work we report on the fabrication process for the development of a flexible piezopolymeric transducer for health monitoring applications, based on lead-free, piezoelectric zinc oxide (ZnO) thin films. All the selected materials are compatible with the space environment and were deposited by the RF magnetron sputtering technique at room temperature, in view of preserving the total flexibility of the structures, which is an important requirement to guarantee coupling with cylindrical fuel tanks whose integrity we want to monitor. The overall transducer architecture was made of a c-axis-oriented ZnO thin film coupled to a pair of flexible Polyimide foils coated with gold (Au) electrodes. The fabrication process started with the deposition of the bottom electrode on Polyimide foils. The ZnO thin film and the top electrode were then deposited onto the Au/Polyimide substrates. Both the electrodes and ZnO layer were properly patterned by wet-chemical etching and optical lithography. The assembly of the final structure was then obtained by gluing the upper and lower Polyimide foils with an epoxy resin capable of guaranteeing low outgassing levels, as well as adequate thermal and electrical insulation of the transducers. The piezoelectric behavior of the prototypes was confirmed and evaluated by measuring the mechanical displacement induced from the application of an external voltage.

Ionic liquid-enhanced soft resistive switching devices

Resistive switching phenomena are of paramount importance in the area of memory devices. In the present study, we have fabricated a simple resistive switching device using a solution processable nanocomposite based on silver nitrate and poly(vinylidene fluoride-hexafluoropropylene). The change in resistance is ascribed to an initial ionic conduction, followed by a non-continuous field induced filament formation. The switching device fabricated with the above-mentioned active matrix displayed a volatile switching behavior. The addition of room temperature ionic liquid plays a fundamental role in triggering permanent memory and reducing the set voltage range up to ten-fold. The change in switching behavior with respect to the applied voltage bias and compliance level set during electrical characterization was studied thoroughly. The present work also gives a glimpse into the importance of device architecture on resistive switching phenomena.

Low-temperature atomic layer deposition of TiO2 thin layers for the processing of memristive devices

Atomic layer deposition (ALD) represents one of the most fundamental techniques capable of satisfying the strict technological requirements imposed by the rapidly evolving electronic components industry. The actual scaling trend is rapidly leading to the fabrication of nanoscaled devices able to overcome limits of the present microelectronic technology, of which the memristor is one of the principal candidates. Since their development in 2008, TiO2 thin film memristors have been identified as the future technology for resistive random access memories because of their numerous advantages in producing dense, low power-consuming, three-dimensional memory stacks. The typical features of ALD, such as self-limiting and conformal deposition without line-of-sight requirements, are strong assets for fabricating these nanosized devices. This work focuses on the realization of memristors based on low-temperature ALD TiO2 thin films. In this process, the oxide layer was directly grown on a polymeric photoresist, thus...

4H-SiC Schottky Barrier Diodes Using Mo-, Ti- and Ni-Based Contacts

We have studied different Schottky and ohmic contacts on 4H-SiC with the aim to obtain Schottky barrier diodes (SBDs) capable to operate at high temperatures, frequencies and power densities for long periods of time, and showing low power losses. The control of the Schottky barrier plays an important role in minimizing the power loss of a SBD, and the metal-semiconductor interface properties strongly affect the overall performances of such a device. Schottky contacts were deposited using Ni, Ti, Ti/Al, Mo and Mo/Al layers, and the annealing treatments have been performed up to 600 °C using a rapid thermal annealing process (RTA). Ohmic contacts have been deposited on the wafer backside using Ti/Al or Ti/Ni/Ag layers. The Schottky diodes have been characterized by means of standard current-voltage (I-V) and capacitance-voltage (C-V) techniques. Schottky diodes with Mo and Mo/Al barriers show a lower barrier height and better overall performances in forward polarization when compared to the Ti- and Ni-based contacts.

Biorecognition in Organic Field Effect Transistors Biosensors: The Role of the Density of States of the Organic Semiconductor

Biorecognition is a central event in biological processes in the living systems that is also widely exploited in technological and health applications. We demonstrate that the Electrolyte Gated Organic Field Effect Transistor (EGOFET) is an ultrasensitive and specific device that allows us to quantitatively assess the thermodynamics of biomolecular recognition between a human antibody and its antigen, namely, the inflammatory cytokine TNFα at the solid/liquid interface. The EGOFET biosensor exhibits a superexponential response at TNFα concentration below 1 nM with a minimum detection level of 100 pM. The sensitivity of the device depends on the analyte concentration, reaching a maximum in the range of clinically relevant TNFα concentrations when the EGOFET is operated in the subthreshold regime. At concentrations greater than 1 nM the response scales linearly with the concentration. The sensitivity and the dynamic range are both modulated by the gate voltage. These results are explained by establishing the correlation between the sensitivity and the density of states (DOS) of the organic semiconductor. Then, the superexponential response arises from the energy-dependence of the tail of the DOS of the HOMO level. From the gate voltage-dependent response, we extract the binding constant, as well as the changes of the surface charge and the effective capacitance accompanying biorecognition at the electrode surface. Finally, we demonstrate the detection of TNFα in human-plasma derived samples as an example for point-of-care application.