Laura Basiricò

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.

A deeper insight into the operation regime of all-polymeric electrochemical transistors

All-Organic Electrochemical Transistors (OECTs) realized by employing Poly(3,4-EthyleneDiOxyThiophene) doped with Poly(Styrene Sulfonate) as conductive polymer show a dependence of their behavior on the gate to channel area ratio. This peculiarity has been investigated and the working mechanism has been explained in view of the behavior of the ionic component of the device. In particular, taking into account the current theory of OECT behavior, we have focused our attention on the role of the gate, trying to clarify if these devices may be considered as working in Faradaic or capacitive regime.

Direct X-ray photoconversion in flexible organic thin film devices operated below 1 V

The application of organic electronic materials for the detection of ionizing radiations is very appealing thanks to their mechanical flexibility, low-cost and simple processing in comparison to their inorganic counterpart. In this work we investigate the direct X-ray photoconversion process in organic thin film photoconductors. The devices are realized by drop casting solution-processed bis-(triisopropylsilylethynyl)pentacene (TIPS-pentacene) onto flexible plastic substrates patterned with metal electrodes; they exhibit a strong sensitivity to X-rays despite the low X-ray photon absorption typical of low-Z organic materials. We propose a model, based on the accumulation of photogenerated charges and photoconductive gain, able to describe the magnitude as well as the dynamics of the X-ray-induced photocurrent. This finding allows us to fabricate and test a flexible 2 × 2 pixelated X-ray detector operating at 0.2 V, with gain and sensitivity up to 4.7 × 104 and 77,000 nC mGy−1 cm−3, respectively.

Inkjet printed arrays of pressure sensors based on all-organic field effect transistors

In this paper we propose totally flexible organic field effect transistors (OFETs) assembled on plastic films as sensors for mechanical variables. First mechanical sensors for pressure and bending detection are presented. A sharp and reversible sensitivity of the output current of the device to an elastic deformation induced by means of a mechanical stimulus on the device channel has been observed and suggested the idea of employing arrays of such sensors for detecting the deformation applied onto a planar surface. Second the possibility of using similar devices for bio- and chemo-detection is described. By exploiting the properties of the basic structure, the device can be combined with any kind of substrate to detect for instance the pressure applied by people walking or standing on a functionalized carpet. This emerging technology seems to be promising for applications in the field of remote and non invasive monitoring of elderly and disabled people.

Organic bendable and stretchable field effect devices for sensing applications

In this paper we propose a detailed investigation on the electrical response of Organic Field Effect Transistors (OFETs) assembled on flexible plastic substrates to mechanical deformations. We will demonstrate that, by applying a surface deformation by an external mechanical stimulus we are inducing morphological and structural changes in the organic semiconductor, giving rise to a marked, reproducible and reversible variation of the device output current. We will show how the intrinsic properties of the employed active layers play a crucial role in determining the final sensitivity to the mechanical deformation. Finally we will also demonstrate that the fabricated flexible system can be successfully employed for different applications that go from the detection of bio-mechanical parameters (joints motion, breath rate, etc.) in the wearable electronics field, to tactile transduction for the realization of artificial “robot skins”.

Space environment effects on flexible, low-voltage organic thin film transistors

Organic electronic devices fabricated on flexible substrates are promising candidates for applications in environments where flexible, lightweight, and radiation hard materials are required. In this work, device parameters such as threshold voltage, charge mobility, and trap density of 13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene)-based organic thin-film transistors (OTFTs) have been monitored for performing electrical measurements before and after irradiation by high-energy protons. The observed reduction of charge carrier mobility following irradiation can be only partially ascribed to the increased trap density. Indeed, we used other techniques to identify additional effects induced by proton irradiation in such devices. Atomic force microscopy reveals morphological defects occurring in the organic dielectric layer induced by the impinging protons, which, in turn, induce a strain on the TIPS-pentacene crystallites lying above. The effects of this strain are investigated by density functional theory simulations of two model structures, which describe the TIPS-pentacene crystalline films at equilibrium and under strain. The two different density of states distributions in the valence band have been correlated with the photocurrent spectra acquired before and after proton irradiation. We conclude that the degradation of the dielectric layer and the organic semiconductor sensitivity to strain are the two main phenomena responsible for the reduction of OTFT mobility after proton irradiation.