| Since the end of last century, organic thin-film transistors (OTFTs) based on conjugated polymers, oligomers, or other molecules have been rapidly developing as a novel alternative to more traditional, mainstream thin-film transistors (TFTs) based on inorganic materials. However, the low performance, such as low field-effect mobility and switching speed, limits the applications of OTFTs. Therefore, to enhance field-effect mobility is the main purpose in this work and the focus is the interface study between dielectric and semiconductor layers. The self-assembling or ordering of semiconductor molecules enhances the pi-orbital overlap and is the key to improvements in carrier mobility. The functional groups of dielectric materials on surface do affect the alignment and the crystal formation of semiconductor. In this study, the dielectric surface was modified to obtain preferred functional groups that promote molecular ordering of semiconductor on the dielectric surface.;Since most of the studies in OTFTs area are on silicon wafer, first, OTFTs were fabricated using heavily p-doped silicon wafers as gate electrode and thermally grown SiO2 as the dielectric. Organosilanes, (3-mercaptopropyl)triethoxysilane (MPTES) and p-tolyltrimethoxysilane (TTMS), were next used to modify the dielectric surface. Solution-processing approach was then used to deposit bis(triisopropylsilylethynyl) pentacene (TIPS) in order to form the organic semiconductor layer. For industrial application requiring large area coverage, structural flexibility, and low cost, such as printed electronics, each layer is printed on the flexible plastic substrate, so the dielectric materials have to be printable or coated simply. Thus, poly(4-vinyl phenol-co-methyl methacrylate) (PVP- co-PMMA) was used as dielectric. The useful surface modification agents studied on silicon wafer were applied on flexible substrate as well. The metal ink was screen printed on cross-linked PVP-co-PMMA to form source and drain. TIPS solution was deposited either by drop casting or rod coating. Electrical characterizations indicated that the field effect carrier mobility was enhanced by about two orders of magnitude for OTFTs fabricated on treated dielectric surface. |
