Alessandra Caboni

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.

Organic-based sensor for chemical detection in aqueous solution

We present a flexible, pentacene-based field-effect device, for the detection of chemical species in aqueous solution. The sensor consists in a double-gate transistor, where the detection is achieved by exploiting the charge sensing capabilities of the floating-gate terminal. To provide the pH-sensitivity, the floating gate is functionalized with thioamine groups as such groups protonize proportionally to the concentration of H3O+ ions in solution. With respect to the existing organic-based devices for pH monitoring, our sensor does not require a counterelectrode and the organic semiconductor is not affected by the contact with the monitored solution.

Flexible Organic Thin-Film Transistors for pH Monitoring

A novel freestanding flexible device based on an organic field effect transistor (OFET), able to detect pH changes in chemical solutions thanks to a functionalized floating-gate, was realized and successfully tested. The device is assembled on a flexible film (Mylar), which acts at the same time as gate insulator and as mechanical support for the whole structure. On one side of the foil a control gate and drain/source contacts are photolithographically patterned, and a pentacene active layer deposited; on the opposite side a gold floating gate is defined. The sensor performs the detection of the chemical species placed over the probe area by detecting the associated electric charge: the structure, basically, works as a floating-gate transistor whose threshold voltage is modulated by the surface charge due to the solution under investigation. By properly functionalizing the floating gate surface, sensitivity to different species and the detection of different reactions can be achieved, with the same sensor. In this work we present its application as ion-sensitive device. pH sensitivity is achieved by functionalizing the sensing surface with thio-aminic groups as such groups protonate proportionally to the concentration of H3O+ ions in the solution. Such a structure does not require a counter-electrode as the OFET is biased through a control gate. Moreover, the working mechanism is independent of the choice of semiconductor, gate or dielectric material, since the OFET is insulated from the solution. The application as DNA sensor is currently under investigation as well.

Producing Smart Sensing Films by Means of Organic Field Effect Transistors

We have fabricated the first example of totally flexible field effect device for chemical detection based on an organic field effect transistor (OFET) made by pentacene films grown on flexible plastic structures. The ion sensitivity is achieved by employing a thin Mylar foil as gate dielectric. A sensitivity of the device to the pH of the electrolyte solution has been observed A similar structure can be used also for detecting mechanical deformations on flexible surfaces. Thanks to the flexibility of the substrate and the low cost of the employed technology, these devices open the way for the production of flexible chemical and strain gauge sensors that can be employed in a variety of innovative applications such as wearable electronics, e-textiles, new man-machine interfaces

A CMOS Biocompatible Charge Detector for Biosensing Applications

A solid-state CMOS device capable of detecting the changes of electric charge caused by a chemical or biological reaction is presented. The device is fully compatible with a standard CMOS process. Biocompatibility is obtained by the passivation of the active area with a layer of alumina obtained with a simple, low-cost, and reliable process. A test chip hosting 80 sensors has been realized and characterized showing the detection capabilities of the novel sensor. The reusability of the device by stripping of the alumina layer was proved.

Integration of a microfluidic flow cell on a CMOS biosensor for DNA detection

This paper describes the fabrication technique for the realization a microfluidic flow cell to be integrated on a CMOS biosensor for DNA hybridization detection. The main element of the microfluidic system is made in polydimethylsiloxane (PDMS) elastomer and takes up an area of 5 mm2. PDMS is cast against a silicon master patterned by deep reactive ion etching (DRIE) and then bonded on the chip by means of oxygen plasma activation. The micro channels patterned in the flow cell are connected with capillary tubes that can be easily interconnected to a common syringe.

Organic field-effect based sensors for body parameters monitoring

In this paper we propose totally flexible organic field effect transistors (OFETs) assembled on plastic films as sensors for physiological parameters monitoring. In the first part, mechanical sensors for pressure and bending detection are presented and some biomedical sensing applications are illustrated. 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 is observed. In the second part, 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 3D bending of a flexible surface and/or for detecting pH of sweat. Robot skin and wearable electronics seem to be promising applications for this emerging technology.

A flexible floating-gate organic thin-film transistor for detection of chemical species

A novel free-standing flexible OFET able to detect pH changes in chemical solutions thanks to a functionalized floating-gate has been realized and successfully tested. The structure includes a control gate on one side of a Mylar foil (on which gold drain/source contacts are photolithographically patterned and a pentacene active layer deposited) and a gold floating-gate on the opposite side of the foil. The floating-gate is functionalized with thio-aminic groups and represents the active area of the device as such groups protonize proportionally to the concentration of H3O+ ions in the solution. Consequently, the control-capacitor and the charge immobilized on the active area concurrently set the actual gate voltage drop on the transistor insulating layer, thus modulating the drain current. Such a structure does not require a counter-electrode and insulates the OFET from the solution, thus the working mechanism is independent of the choice of semiconductor, gate or dielectric material.