In Organic Thin Film Transistors (OTFTs), the performance is profoundly affected by organic semiconductor crystal formation or organic structure ordering. As it is known, the ability of conjugated molecules to transport charge due to the p-orbital overlap of neighboring molecules provides their semiconducting and conducting properties. The self-assembling or ordering of these molecules enhances this p-orbital overlap and is the key to improvements in carrier mobility. Since the semiconductor materials are deposited on dielectric layer, the surface chemical and mechanical properties of dielectric materials do affect the alignment and the crystal formation of semiconductor. In this work, we present methods about dielectric surface modification to obtain preferred functional group and promote semiconductor ordering on dielectric surface.

OTFTs were made on heavily doped silicon wafer and the thermally grown SiO₂ was modified by organosilanes which have different functional groups, such as –SH, -C₆H₅. Those functional groups help the assembling of semiconductor molecular on dielectric surface. A field effect carrier mobility of 0.01 cm²/V•s was obtained for OTFTs with solution processable bis(triisopropylsilylethynyl) (TIPS) pentacene. X-ray photoelectron spectroscopy was used to characterize the chemical composition of modified dielectric surface. More ordered semiconductor crystal structure was shown by atomic force microscopy after surface treatment.