Study Of Thiophene DPP Polymer Semiconductor Materials And The Performance Of OTFT Devices

In recent years,the research of organic thin film transistor(OTFT)has developed rapidly,but in practical applications,there are still many problems,such as low mobility,high working voltage,large sub threshold swing,etc.Therefore,based on a new type of thiophene DPP(diketopyrrolopyrrole)polymer semiconductor material,we analyzed the influence and mechanism of the molecular structure of the polymer material on the performance of the OTFT devices.The effects of preparation process and different insulating materials on the performance of organic thin film transistors are analyzed by different solvent systems and different preparation processes.The specific research contents are as follows:(1)The influence of molecular structure of polymer semiconductor materials on the performance of OTFT devicesBased on the new thiophene DPP polymer semiconductor materials provided by Corning,we studied the influence mechanism of the I type straight side chain structure and the Y type bifurcate side chain structure on the semiconductor properties.Found that the Y type bifurcate chain structure can improve the solubility of the polymer material and make it better dispersed in the solvent system,while the I type direct chain structure is beneficial to the enhancement of the ?-? accumulation between the polymer molecules and the increase of the crystalline density of the polymer.In addition,the side chain structure also affects the structure of the polymer conjugate surface,the crystallization orientation of the polymer and the molecular weight of the synthetic materials,which will further affect the semiconductor properties of the polymer materials.The relevant analysis pointed out the direction of design and synthesis of high performance polymer semiconductors.(2)Effects of solvent system and preparation process on the performance of organic thin film transistorsNew thiophene polymer thin film transistors are prepared on the substrate of heavily doped silicon wafers with thermally grown silicon dioxide insulating layer.The effect of polymer semiconductor solvent and annealing process on the performance of the OTFT device were studied in detail,and then the related mechanisms in the process were discussed.The mechanisms of surface self-assembly and the effect of surface modification on the performance of SiO2 insulating layer were studied.Finally the optimized mobility of the polymer thin film transistors was>2 cm2V-1s-1,and the current switch ratio was>107,which was in the forefront level of the same type materials.The study provides a reference for the preparation of high performance organic thin film transistors.(3)Study on properties of epoxy resin SU8 photoresist insulating layerWhen OTFT devices prepared on the silicon dioxide insulating layer,surface modification is necessary to reduce the surface energy and then achieve good device performance.Meanwhile polymer insulation materials have better compatibility with polymer semiconductors,and good device performance can be achieved without modification.SU8 photoresist has been widely used in the field of MEMS,however,there are few reports on the application of insulating layer in thin film transistors.Therefore,the possibility of SU8 photoresist be used as the gate insulating layer in thin film transistors was explored.By changing the solvent ratio of SU8 photoresist,it can keep the properties of the photoresist,while the film thickness can be reduced to a suitable range for the thin film transistors.Through the analysis and optimize of the preparation process of SU8 insulating layer,it can bear 100V without breakdown,and the leakage current density was about 0.5 nA/cm2@1 MV/cm,the insulation performance was in the forefront level of polymer insulations reported.The graphical process of SU8 insulating layer was studied to keep the photoresist characteristics in order to facilitate the practical application.OTFT devices were prepared based on SU8 insulating layer,without modification,the mobility of the device can reach 0.9 cm2V-1s-1,further more,the flexible OTFT devices possessed good electrical and mechanical properties.(4)Study on the properties of high k material zirconia insulating layerAiming at the problems of high working voltage and large subthreshold swing of OTFT devices fabricated on low k insulating materials,a high k material insulation layer based on zirconium oxide was developed.By introducing new ligands oleic acid,the problem of poor film formation was solved.The zirconium oxide film prepared by UV light annealing and thermal annealing was compared.The mechanism of the leakage current density and dielectric constant of zirconia film were analyzed,which indicates the direction of improving the related properties of zirconia thin film.On the basis of this study,the surface defects of zirconia film are further reduced by O2 plasma treatment,and its insulation performance and thermal stability were improved.The dielectric constant of the insulating layer is further improved by adding titanium element in the film,and the dielectric constant of the film can be adjusted by controlling the proportion of titanium,which meets the needs of different applications.Finally,high performance zirconia insulating film was prepared by UV light low temperature annealing process.Based on this,we successfully fabricated organic thin film transistors with low working voltage and low subthreshold swing.