Design And Fabrication Of Novel Polymer Dielectric Materials For Application In Organic Thin Film Transistors

Organic thin film transistors（OTFTs）,as an important part of the field of microelectronics technology,shine in emerging electronics such as flexible displays,chemical/biological sensors,radio frequency identification tags,and wearable electronic devices.After several generations of efforts,the OTFTs device mobility has been obviously improved from the original 10^-5 cm²/Vs to 1 cm²/Vs,and can even rival the level of single crystal silicon.Compared with inorganic metal oxide transistors,OTFTs have not effectively solved the problems of adjusting semiconductor crystal growth and achieving low-voltage operation OTFTs.However,for the aforementioned problems,in addition to semiconductors,the surface properties and dielectric constant of the dielectric layer affect the growth of the semiconductor crystal and the operational voltage,respectively.Conventional inorganic oxide materials can achieve low-voltage operation OTFTs due to their large dielectric constants,but they have drawbacks,such as large surface roughness,high temperature processing,and poor compatibility with organic semiconductors,which make them limitated in the application of OTFTs device.Polymer-based dielectric layers are ideal candidates due to their smooth surfaces,low-temperature solution processability,and easy compatibility with organic semiconductors.Furthermore,they have excellent mechanical flexibility and can be easily tailored by molecular design and chemical synthesis,which can be easily functionalized to meet a variety of purposes.Therefore,the development and fabrication of novel functional polymer materials is of great significance for organic thin film transistors.The introduction of Chapter 1,we briefly reviewed the development history and main application areas of organic thin film transistors.At the same time,we also introduced the basic device structure of organic thin film transistors,OTFTs operation principles and semiconductor materials as well as dielectric materials.In the part 2 of this thesis,we copolymerized a monomer containing naphthyl group with 2-hydroxyethyl methacrylate（HEMA）and glycidyl methacrylate（GlyMA）in various molar ratio to obtain copolymers as functional gate dielectric layers of organic thin-film transistors.Using naphthyl-containing molecule to have similar chemical structure with pentance to adjust the grain size of semiconductor.The results indicated that as molar percentage of naphthyl-containing compound in the polymer structure increased,the density of the pentacene nucleation increased and pentacene grain size decreased,larger and more uniform pentacene grain size favored to achieve higher mobility in the OTFTs devices,the average mobility of the device is up to 0.31cm²/Vs.Therefore,our results indicated an effective strategy for the design on the insulator polymer as gate dielectric to induce larger and more uniform semiconductor grain size for improving the mobility of OTFTs devices.In the part 3 of this thesis,we designed and synthesized a alkylated terphenyl monomer and a alkylated terphenyl monomer containing a cyano group,they can copolymerize with 2-hydroxyethyl methacrylate（HEMA）and glycidyl methacrylate（GMA）to afford solution-processable polymers,which displayed high k values of 6.8and 8.6,suggesting that the introduction of cyano groups can increase the dielectric constant of polymers effectively.These copolymer materials can be easily processed into smooth and pinhole-free films by a simple solution spin-coating.At the same time,they had low surface roughness and no defects,and they also had low leakage current density and small dielectric loss tangent values,indicating that they have better insulation properties.With these novel polymer dielectric layers,VOPc/p-6P transistors were fabricated,which granted excellent charge carrier mobility of 0.52 and 0.1 cm²/Vs,current on/off ratio?10⁴.In the part 4 of this thesis,cyclic carbonates（CC）have been reported to have high dielectric constant because of high dipole moment,so we designed and synthesized a monomer containing cyclic carbonate,which copolymerized with 2-（2-methoxyethoxy）ethyl methacrylate（MEEMA）and glycidyl methacrylate（GMA）to afford solution-processable polymers.They exhibited high-k up to 7¹0 depending on the content of cyclic carbonate.These copolymer materials can be easily processed into smooth and pinhole-free films by a simple solution spin-coating,which exhibited good solvent-resistance and flexibility.Moreover,they displayed low leakage current densities,small dielectric loss and excellent dielectric properties,indicating a good application prospect in low-voltage operating OTFTs.As a result,good field-effect characteristics were achieved in our p-type C₁₀-DNTT OTFTs based present copolymers as the gat dielectrics.Further,the mobility increased with the increase of the k values of the copolymers as the gate dielectric,with the highest average mobility of 9.7 cm²/Vs at low operation voltage below than 10 V achieved in the C₁₀-DNTT OTFTs,and the C₁₀-DNTT OTFTs exhibited high on/off current ratio of about 10⁵.Our results indicates that the present copolymers have a good application prospect in the low-voltage operating OTFTs.