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Discusses a study which presented an analytical model that describes the operation of a-hexathienylene thin-film-transistors (TFT). Calculation of the current-voltage characteristics of TFT; Factors considered in the use of the model; List of organic materials.

Thin polycrystalline films of perylenetetracarboxylic dianyhydride (PTCDA), an organic molecular solid, exhibits substantial anisotropies in its electronic transport properties. Only electrons transport in the directions along molecular planes, while mainly holes transport in the direction normal to molecular planes. A series of measurements on both field effect transistors with PTCDA active layers and light emitting diodes with PTCDA transport layers documents the anisotropy seen in the electronic transport in thin films of PTCDA. © 1997 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Electrolyte gated thin film transistors (TFTs) based on sol–gel processed zinc oxide (ZnO) are investigated using imidazolium-based ionic liquids (ILs), namely [bmim][BF4] and [bmim][PF6], as electrolytes. The capacitance of the ILs is determined by means of electrochemical impedance spectroscopy. The frequency dependence of the capacitance measurements indicates that the electric double layers (EDLs) form below 1 kHz. Impedance measurements are also acquired at different gate voltages and the effect of the bias is discussed in detail. The experimental data suggest that the double layer capacitance of the two ILs depends on the polarization voltage. In terms of transistor characteristics, minimum hysteresis is observed in the case of [bmim][BF4]. Being smaller in size out of the two, a higher ionic mobility is expected. Therefore, faster formation of the EDL can account for suppressed hysteresis in the I–V characteristics. The estimated capacitance was 1.17 μF cm−2 for [bmim][PF6] and 4.05 μF cm−2 for [bmim][BF4], which resulted in a TFT field-effect mobility as high as 6.0 and 1.4 cm2 V−1 s−1, respectively. Also the on–off ratio of the EG-TFT is particularly high, being 104. Moreover, transient current measurements showed that the two ILs behave differently under continuous bias stress. The effect of the metal gate electrode on the device characteristics is also investigated. Five metals of varying work functions are employed for establishing a gate/IL interface. The data do not support that there is a correlation between the threshold voltage and the work function of the metals. On the other hand, the capacitance seems to be more susceptible to changes of the metal gate. [ABSTRACT FROM AUTHOR]

Printable and flexible thin-film transistors (TFTs) have gained significant attention over the last few years thanks to their implementation in many different sectors. Beside applications in large-area electronics such as flat displays, sensors and radio frequency identification tags, these devices have been widely investigated for life sciences applications too, including label-free biosensors, systems for drug delivery and implantable platforms. This review highlights the recent advances in the field of highly performing low-cost TFT devices realized by printing or printing compatible technologies and suitable for bioelectronics applications. Novel printable materials used as semiconductors, dielectrics and electrodes as well as printing technologies useful for the realization of the elicited devices are discussed as well. Particularly attention is given to printing techniques employed for the deposition of biological materials and to methods for realizing label-free electronic biosensors. [ABSTRACT FROM AUTHOR]

A simple and time-saving wet method to endow the surface of organic semiconductor films with carboxyl functional groups is presented. A thin layer of poly(acrylic acid) (pAA) is spin-coated directly on the electronic channel of an electrolyte-gated organic FET (EGOFET) device and cross-linked by UV exposure without the need for any photo-initiator. The carboxyl functionalities are used to anchor phospholipid bilayers through the reaction with the amino-groups of phosphatidyl-ethanolamine (PE). By loading the membranes with phospholipids carrying specific functionalities, such a platform can be easily implemented with recognition elements. Here the case of biotinylated phospholipids that allow selective streptavidin electronic detection is described. The surface morphology and chemical composition are monitored using SEM and XPS, respectively, during the whole process of bio-functionalization. The electronic and sensing performance level of the EGOFET biosensing platform is also evaluated. Selective analyte (streptavidin) detection in the low pM range is achieved, this being orders of magnitude lower than the performance level obtained by the well assessed surface plasmon resonance assay reaching the nM level, at most. [ABSTRACT FROM AUTHOR]

A jellified alginate based capsule serves as biocompatible and biodegradable electrolyte system to gate an organic field-effect transistor fabricated on a flexible substrate. Such a system allows operating thiophene based polymer transistors below 0.5 V through an electrical double layer formed across an ion-permeable polymeric electrolyte. Moreover, biological macro-molecules such as glucose-oxidase and streptavidin can enter into the gating capsules that serve also as delivery system. An enzymatic bio-reaction is shown to take place in the capsule and preliminary results on the measurement of the electronic responses promise for low-cost, low-power, flexible electronic bio-sensing applications using capsule-gated organic field-effect transistors. [ABSTRACT FROM AUTHOR]

In the present study, Au-surfactant core-shell colloidal nanoparticles (NPs) with controlled dimension and composition were synthesized by sacrificial anode electrolysis. Transmission electron microscopy (TEM) revealed that Au NPs core diameter is between 8 and 12 nm, as a function of the electrosynthesis conditions. Moreover, surface spectroscopic characterization by X-ray photoelectron spectroscopy (XPS) analysis confirmed the presence of nanosized gold phase. Controlled amounts of Au NPs were then deposited electrophoretically on carbon nanotube (CNT) networked films. The resulting hybrid materials were morphologically and chemically characterized using TEM, SEM (scanning electron microscopy) and XPS analyses, which revealed the presence of nanoscale gold, and its successful deposition on CNTs. Au NP/CNT networked films were tested as active layers in a two-pole resistive NO2 sensor for sub-ppm detection in the temperature range of 100-200 °C. Au NP/CNT exhibited a p-type response with a decrease in the electrical resistance upon exposure to oxidizing NO2 gas and an increase in resistance upon exposure to reducing gases (e.g. NH3). It was also demonstrated that the sensitivity of the Au NP/CNT-based sensors depends on Au loading; therefore, the impact of the Au loading on gas sensing performance was investigated as a function of the working temperature, gas concentration and interfering gases. [ABSTRACT FROM AUTHOR]

We show that organic thin-film transistors have suitable properties for use in gas sensors. Such sensors possess sensitivity and reproducibility in recognizing a range of gaseous analytes. A wealth of opportunities for chemical recognition arise from the variety of mechanisms associated with different semiconductor-analyte interactions, the ability to vary the chemical constitution of the semiconductor end/side groups, and also the nature of the thin-film morphology. [ABSTRACT FROM AUTHOR]