Piero Cosseddu

Towards the textile transistor: Assembly and characterization of an organic field effect transistor with a cylindrical geometry

Cylindrical organic field effect transistors have been obtained starting from a metallic fiber used in textile processes. The metal core of the yarn, covered with a thin polyimide layer, is the gate of the structure. A top-contact device can be obtained by depositing a layer of organic semiconductor followed by the deposition of source and drain top contacts, made by metals or conductive polymers, deposited by evaporation or soft lithography. Thanks to the flexibility of the structure and the low cost of technologies, this device is a meaningful step towards innovative applications of textile electronics.

Tetracene light-emitting transistors on flexible plastic substrates

We report on organic light-emitting (field-effect) transistors (LETs) fabricated on a flexible and transparent plastic foil (Mylar), acting both as substrate and gate dielectric. The foil is patterned on one side with bottom-contact gold source and drain electrodes, while a thin film of gold is evaporated on the opposite side of the foil to form the gate electrode. A vacuum sublimed tetracene film is employed as an active layer for charge transport and light emission. Atomic force microscopy shows that tetracene films have a good adhesion on Mylar and exhibit a granular structure. The transistor shows unipolar p-type behavior with mobilities typically of 5×10−4cm2∕Vs. Drain-source current and electroluminescence have been simultaneously measured. Provided a suitable gate bias is applied, light emission occurs at drain-source voltages (Vds) above saturation. LETs on plastic substrates could open the way to flexible devices combining the switching function of a transistor and the light emission.

Ultralow Voltage, OTFT‐Based Sensor for Label‐Free DNA Detection

An organic ultralow voltage field effect transistor for DNA hybridization detection is presented. The transduction mechanism is based on a field-effect modulation due to the electrical charge of the oligonucleotides, so label-free detection can be performed. The device shows a sub-nanometer detection limit and unprecedented selectivity with respect to single nucleotide polymorphism.

Soft lithography fabrication of all-organic bottom-contact and top-contact field effect transistors

All-organic field effect transistors on flexible plastic substrates have been fabricated. A thin Mylar® foil acts both as substrate and gate dielectric. The contacts have been fabricated with poly(ethylene-dioxythiophene)/polystyrene sulfonate (PEDT/PSS) by means of soft lithography. The active layer (pentacene) is vacuum sublimed on the prepatterned film in case of bottom-contact devices or, in case of top-contact devices, the active layer sublimation is made in advance. On the opposite side of the foil, a thin PEDT/PSS film, acting as gate electrode, is spin coated. The comparison between top-contact and bottom-contact devices shows interesting characteristics as a marked difference in the ID versus VD curve that can be mainly attributed to a different quality of PEDT/PSS-semiconductor contact. The flexibility of the obtained structure and the easy scalability of the technological process open the way for economic production of high resolution organic devices.

Ultra-low voltage, organic thin film transistors fabricated on plastic substrates by a highly reproducible process

Organic thin film transistors have been fabricated on plastic substrates using a combination of two ultrathin insulating films, namely a 6 nm Al2O3 film (grown by UV-Ozone treatment of a pre-deposited aluminium film) and a 25 nm parylene C film deposited by vapour phase, as gate dielectric. They show a very low leakage current density, around 2 × 10−9 A/cm2, and, most importantly, can be operated at voltages below 1 V. We demonstrate that this low-cost technique is highly reproducible and represents a step forward for the routine fabrication of ultra-low voltage plastic electronics.

Piezoelectric Polymer Transducer Arrays for Flexible Tactile Sensors

The paper focuses on the manufacturing technology of modular components for large-area tactile sensors, which are made of arrays of polyvinylidene fluoride (PVDF) piezoelectric polymer taxels integrated on flexible PCBs. PVDF transducers were chosen for the high electromechanical transduction frequency bandwidth (up to 1 kHz for the given application). Patterned electrodes were inkjet printed on the PVDF film. Experimental tests on skin module prototypes demonstrate the feasibility of the proposed approach and reveal the potentiality to build large area flexible and conformable robotic skin.

Active Devices Based on Organic Semiconductors for Wearable Applications

Plastic electronics is an enabling technology for obtaining active (transistor based) electronic circuits on flexible and/or nonplanar surfaces. For these reasons, it appears as a perfect candidate to promote future developments of wearable electronics toward the concept of fabrics and garments made by functional (in this case, active electronic) yarns. In this paper, a panoramic view of recent achievements and future perspectives is given.

An organic transistor-based system for reference-less electrophysiological monitoring of excitable cells

In the last four decades, substantial advances have been done in the understanding of the electrical behavior of excitable cells. From the introduction in the early 70s of the Ion Sensitive Field Effect Transistor (ISFET), a lot of effort has been put in the development of more and more performing transistor-based devices to reliably interface electrogenic cells such as, for example, cardiac myocytes and neurons. However, depending on the type of application, the electronic devices used to this aim face several problems like the intrinsic rigidity of the materials (associated with foreign body rejection reactions), lack of transparency and the presence of a reference electrode. Here, an innovative system based on a novel kind of organic thin film transistor (OTFT), called organic charge modulated FET (OCMFET), is proposed as a flexible, transparent, reference-less transducer of the electrical activity of electrogenic cells. The exploitation of organic electronics in interfacing the living matters will open up new perspectives in the electrophysiological field allowing us to head toward a modern era of flexible, reference-less, and low cost probes with high-spatial and high-temporal resolution for a new generation of in-vitro and in-vivo monitoring platforms.

Organic light-emitting transistors using concentric source/drain electrodes on a molecular adhesion layer

Bottom-contact tetracene light-emitting transistors employing a mercaptosilane derivative self-assembled monolayer as adhesive between gold concentric interdigitated source/drain electrodes and SiO2 gate dielectric are described. Devices that employ the mercaptosilane adhesive have a higher mobility and electroluminescence compared to those employing a standard metallic adhesive. This is rationalized in terms of the large, well interconnected grains found in tetracene films deposited on substrates using the mercaptosilane adhesive. Our work represents a step forward in the understanding of physical processes at semiconductor/metal and semiconductor/dielectric interfaces in organic devices.

Strain Sensitivity and Transport Properties in Organic Field-Effect Transistors

We present the electromechanical characterization of organic field-effect transistors (OFETs) fabricated with different organic semiconductors. Pentacene- and poly(3-hexylthiophene-2,5-diyl) (P3HT)-based OFETs have been investigated as strain sensors, and a clear correlation between the structural and morphological properties of the active layer with the device sensitivity has been observed. The highly disordered structure of polymeric films, as P3HT, confirmed by morphological and structural investigations, gives rise to a dramatic reduction of the device response to mechanical stimuli. Nevertheless, an unambiguous, fast, and reproducible response has been obtained also for this material, which, being solution processible, represents a valuable solution for the fabrication of low-cost pressure sensors for a variety of innovative applications.