Study On Organic Field-efeect Transistor Gas Sensors Based On Silk Fibroin

Organic field-effect transistors(OFETs), also called organic thin-film transistors, are a kind of organic electronic devices, which are developed on the basis of inorganic field-effect transistors(FETs). The OFET devices, with several advantages such as lower power consumption, less weight, and smaller size, have attracted great interests and concerns of worldwide scientific researchers since they were reported for the first time. At present, the OFETs, whose performance have approached or even exceeded the level of a-Si:H FETs, are expected to be widely used in organic light-emitting diode displays and large scale integrated circuit. With the development of organic sensitive materials, OFETs could also be applied in the detection of chemical analytes and gases.In this work, OFETs with the “bottom-gate” and “top-contact” configuration were fabricated by using poly(methyl methacrylate)(PMMA) and silk fibroin(SF) as the dielectric layer, and pentacene as the active layer. PMMA/SF and pentacene thin films were deposited onto a tin indium oxide(ITO) glass substrate by spin coating and vacuum evaporation, respectively. The electrical characteristics and the nitrogen dioxide(NO2) gas sensing characteristics of the OFETs were investigated and its mechanism was in further discussion. Besides, the survey reveals that the transistor performance is dependent on the process conditions to a certain extent.1. OFET NO2 gas sensors consisted of SF dielectric layer were studied. Pentacene OFETs with PMMA, SF and PMMA/SF bilayer dielectrics were fabricated. Compared to those based on single PMMA or SF dielectric devices, the OFETs with PMMA/SF bilayer dielectric exhibited the optimal electrical characteristics. Then, the gas sensing characteristics of the OFETs with PMMA/SF bilayer dielectric were studied. The results showed that PMMA/SF based OFETs exhibited a good level of performance particularly in terms of response speed and response rate when exposed to NO2 gas at room temperature, with an ultralow detect limitation of 10 ppm. Meanwhile, the morphology of the dielectric layer and the crystalline state of the active layer were studied by means of atomic force microscopy(AFM). The AFM results indicated that the performance enhancement was mainly attributed to the large surface area and porous structure of SF thin film and the strong interaction between amidogen/hydroxyl and NO2 molecules.2. The influence of solvent-vapor-assisted annealing on the SF based OFETs was also studied. After the high performance OFETs based on PMMA/SF bilayer dielectric were prepared, the method of annealing was optimized to enhance the electrical characteristics of SF based OFET. The results showed that assisted annealed by ethanol before thermal annealing, the OFETs with PMMA/SF bilayer dielectric formed a less interface trap density and a low contact resistance, leading to higher field-effect mobility. In addition, the results described above indicated that the interaction between amidogen/hydroxyl and NO2 molecules played the most important role on the enhancement of gas sensing performance.In summary, the OFET NO2 gas sensors based on silk fibroin were studied to lay a foundation for the application of biological materials to OFET gas sensors.