Design And Preparation Of Polymer Dielectrics For Flexible OFETs

As an important class of flexible electronic devices,organic field-effect transistors(OFETs)possess advantages of lightness,low-cost and easy processing,which show promising applications in electronic-skins,intelligent sensing and memory devices,etc.In addition to organic semiconductors and electrode materials,control of gate dielectrics is also vital to improve the OFET performance.Currently,one of the important issues in this field is to obtain thickness-insensitive polymer dielectrics with high capacitances for achieving low-voltage and high performance flexible OFETs.Therefore,we develop a series of polymer composite dielectric films with high capacitance,which derived from polyelectrolyte materials to reduce the operating voltages and improve device performance of flexible OFETs.The relationship between dielectric films and the OFET performance is also investigated.Then,low-voltage and highly sensitive pressure sensors are designed based on the optimized dielectrics and flexible OFET devices.The main research contents of this thesis include the following three parts:1.A series of binary polymer composite dielectric films with tunable permittivity are developed by introducing higher permittivity polyacrylic acid(PAA)into poly(methyl methacrylate)(PMMA).Compared with the pristine PMMA,the novel PMMA:PAA dielectrics can effectively improve charge mobilities of the flexible OFETs and greatly reduce the operating voltage to-5 V.Meanwhile,the flexible OFET devices show excellent bending stability under different bending radii and cycles.2.A series of novel polyelectrolyte composite dielectric films with different proportions of polyethylene glycol(PEG)and PAA are fabricated by solution processing.Then the effects of films on the performance of flexible OFETs are investigated.The optimized low-voltage OFETs with best performance can work at-0.7 V and exhibit a maximum mobility of 1.28 cm2 V-1 s-1.Compared with the pure PAA,the composite PAA:PEG films greatly enhance the dielectric properties and mechanical robustness due to the effective combination and crosslinking between PAA and PEG.As a result,the corresponding flexible OFETs achieve improved electrical properties and excellent flexibility and stability under different bending conditions.3.A new type of OFET-based pressure sensors is designed with a suspended semiconductor/dielectric/gate structure.By applying different pressures,the interface contact between the semiconductor layer and the source/drain electrodes is changed,causing a gradually increased current in response to the external pressure.Benefiting from the PAA:PEG composite dielectric and the new suspended device structure,a high sensitivity of 452.7 kPa-1 is achieved for the pressure sensors with a low-operating voltage of-0.7 V.Meanwhile,the sensors not only have fast response time and good operating stability,it can also satisfy different pressure detection ranges for practical applications by tuning the suspended gap space.