Development and Characterization of Flexible Double-Gate Organic Transistors for Sensing Applications

Organic electronics is the starting point of a new kind of technology that’s gained a lot of interest in the latest decades of the 20th century and continues now in the 21st century. The possibility to realize flexible devices in a large area gives this field of research a particular interest, since it opens the doors to a multitude of new possible applications. Particular interest has been given to the possible biological and biomedical aspects of such technology, thanks to the possibility to realize flexible devices that could fit inside clothes and adhere to the body, to acquire data with more precision. Conformable devices, realized using ultra-thin substrates, have been employed for artificial skin, a logical consequence of the flexibility properties of such materials. Effects of deformation are discussed and analysed, since integrity of devices is paramount to the effectiveness of this technology. Since its invention, a multitude of transistor architecture have been proposed and explored, to always find new or better solutions to problems and, with the discovery of conduction properties, flexibility, as well as durability and reliability, gained importance when designing a new device. One architecture in particular garnered attention in the scientific scope and is explored and studied in a lot of different configurations, possibilities of use, and advantages that offers. The double-gate architecture, both in inorganic and organic electronics, is vastly used and studied, as it presents itself as a platform for the realization of versatile devices, from circuitry to sensing. As a matter of fact, as will also be presented in this thesis, this architecture has multiple advantages, such as the possibility to tune the threshold voltage, allowing to design circuits realized with a number of devices that all have the same working point. Moreover, the top gate of these structures can be used as a sensing platform, effectively realizing a sensor for mechanical quantities such as temperature and force; ideally, therefore, when properly tuned and characterized, they could be employed for the realization of artificial skin, granting fundamental capabilities to those who lost them. Alternatively, it can be properly functionalized for the recognition of biological species, effectively becoming a biosensor. Of course, when considering these, biocompatibility of materials is a primary property that material must have. The main target of this PhD research activities is to report a thorough study on the aforementioned architecture, with a focus on its multiple beneficial aspects, and investigate the mechanical properties of organic semiconductors. One of the benefits of using such architecture is to tackle a problem that afflicts organic electronics, the degradation of the active layer, that thanks to its self-encapsulating nature, double-gates effectively counter. After a brief introduction about flexible electronics in chapter 1, a state of the art on organic electronics specifically regarding the double gate architecture is presented in chapter 2. Materials and methods, as well as the instrument used, are described in the relative section of chapter 3. Chapter 4 delves into the description of the fabrication and optimization process followed to realize the double gate structure. The mechanical characterization of the devices as temperature and force sensors, both separately and in multimodal mode is reported in chapter 5. Finally, effects of mechanical deformation on different semiconductor are reported in chapter 6, as well as a preliminary characterization of strain sensors. In conclusion, a summary of the results obtained is reported.