Using Silane Molecules For Self-assembly In Organic Thin-film Transistors

Organic thin-film field-effect transistors (OTFTs) are considered to be the key component in next-generation flexible displays which demand prompt response and extreme portability and flexibility. Many hard-to-achieve characteristics in inorganic display manufacturing can easily be achieved with these organic counterparts, including low temperature processing, compatibility with inkjet printing, and versatility in chemical structure design. Therefore, OTFTs recently generated a serious level of interest in the civilian and defense industry. While there are many promising OTFTs materials available, lack of surface compatibility with a gate insulator or dielectric support (mainly silicon oxides) makes their applications in future high-end devices questionable. In this thesis, we focus our attention on the interface between the organic semiconductor materials and the inorganic support.In the first part of the thesis, we chose two organosilane molecules (with a formula of R-SiX3, where R is an alkyl group and X for OEt) to study their thin film self-assembly behavior. We found hierarchical buckling features by annealing a water-rich lamellar structure. This multistacked structure is a direct self-assembly from aminopropyltriethoxysilane, which the polar amine groups promoted the absorption of a large amount of water. We found the resulting soft structures are good candidates to allow the formation of a complex buckling along surface normal. Revealed cauliflower-like, hierarchical patterns are modeled by considering rigid columns standing on a soft substrate. This has helped us understanding the complex buckling problem in a triple-element system. In return, the hierarchical structures demonstrated could find applications in nanofabrication and enrich emerging fields like flexible electronics or optics.The second part of the thesis was focused on using self-assembled thin films of organosilane for OTFTs. Top-contact N-type OTFTs based on PTCDI-C8 (N,N'-dioctyl-Perylene-3,4,9,10-tetracarboxylic acid diimide) was prepared using monolayer coated silicon oxides as the gate insulator and silver as the drain and source electrodes. The PTCDI-C8 thin film as the most important part of OTFT was deposited on substrate by vacuum thermal evaporation. Our initial results showed that the self-assembled polar films played an active role in promoting carrier mobility and the on-off current ratio, as well as reducing the threshold voltage for OTFTs. We assign such an improvement to the organic/inorganic hybrid monolayer, which reduced the surface mismatch between the inorganic insulator (SiOx) and organic semiconductor film (PTCDI-C8). Furthermore, this result suggests that carrier density in OTFTs could be regulated by designing an interface layer of self-assembling capability.