Study On The Design, Preparation And Performance Of Novel Dielectric Polymers For Organic Thin Film Transistors

The integration of organic electronics has created a “smarter” world, which is of great interest for use in electronic papers1, flexible RFID tags, bioelectronics and intelligent textiles. As one of the basic elements for organic logic circuit, the organic thin-film transistors(OTFTs) have been widely studied due to their unique advantages such as light-weight, low-cost, solution-processable and flexibility. Over the past two decades, the charge carrier mobility of OTFTs has approached to the level of amorphous silicon devices. However, compared with inorganic silicon devices, OTFTs has a poor stability and relatively high a threshold voltage, which can lead to higher power consumption in the application. So it is very important to develop the novel insulation polymer materials with superior performance to solve such problem.In the first chapter of this paper, we reviewed the development history and application of OTFTs, expounded the device structure of OTFTs and the basic way of working and introduced the semiconductor layer material and dielectric layer material of OTFTs.In the second chapter of this paper, we designed and synthesized organic/inorganic hybrid dielectric material containing novel silicon nanoparticles and polymer material. The novel silica nanoparticles have excellent dispersion. And the silica nanoparticles with organic groups on their surface can react with the polymers by using chemical bonds. A novel high-k, flexible, and solution-processable organic/inorganic hybrid dielectric material was obtained by mixing the silicon nanoparticles with polyacrylate polymer. With the organic/inorganic hybrid dielectric material as dielectric layer, the p-6P/VOPc OTFTs exhibit low operating voltages and excellent field-effect mobility(0.7 cm2/Vs).In the third chapter of this paper, we designed and synthesized a series of monomers with biphenyl structure. The novel monomers can be copolymerized with 2-hydroxyethyl methacrylate(HEMA) and glycidyl methacrylate(GMA) to form a high-k, flexible, and solution-processable polymer. With the novel polymer as dielectric layer, the p-6P and VOPc OTFTs exhibit low operating voltages(-10 V,-3 V and +3 V, respectively) and excellent field-effect mobility(0.15 cm2/Vs, 0.8 cm2/Vs and 0.5 cm2/Vs, respectively). Although the capacitance of the polymer films do not achieve an excellent level compared with inorganic films and ultrathin films(400 nF/cm2), the OTFTs with the polymer films as dielectric layer exhibit low operating voltages and excellent field-effect mobility. The results demonstrate that the excellent compatibility between polymer films and organic semiconductors provide a large effective capacitance in OTFTs, which is beneficial for operating voltages. At the same time, the introduction of cyano group can effectively increase the dielectric constant of polymer.In the fourth chapter of this paper, we designed and synthesized a novel monomer containing anthracene and olefin groups to determine the relationship between the grain sizes of semiconductor and electron mobility. This monomer can copolymerize with 2-hydroxyethyl methacrylate(HEMA) and glycidyl methacrylate(GMA) to form a solution-processable polymer. In this polymer, the anthracene group possesses a similar structure with organic semiconductor materials, such as pentacene, and can provide crystal nucleus for semiconductor. We synthesized four similar structure polymers by adjusting the mole ratio of novel monomers in structure. Bi-layer dielectric layer(plasma-enhanced chemical vapor deposition SiNx film layer and polymer layer) was used to fabricate bottom-gate top-contact pentacene TFTs to obtain good insulation. With increasing novel monomer content, the dielectric layer can provide substantial crystal nucleus for organic semiconductor and then change the grain sizes of pentacene. Owing to the similar surface performance of these polymer dielectric layers, the relationship between the grain sizes of pentacene semiconductor and field-effect mobility(0.7 cm2/Vs) is concluded under a single variable.