Study On The Flexible Organic Field-effect Transistors Based On Triple Gate Dielectric Layers

The research of flexible low voltage high performance OFETs plays a vital role for flexible low power consumption devices, large area of organic electronic components and memory devices. The extensive existing research of flexible OFETs are complex with large operating voltage, the mobility of the devices are relatively low, the preparation of flexible OFETs are faced with the problems of stability in the actual circuit, such as the bias stability, thermal stability and mechanical stability etc., so the use of simple spin polymer material preparation which can realize low voltage operation and has high mobility on the stability of the flexible OFETs have great significance.Based on the early stage of the research work, we take the PET as the flexible substrate, through the analysis of different methods of the dielectric layers,the roughness of the surface and the contact angle of the dielectric layers, pentacene morphology and electrical properties of the device, we constant optimization experiments to find the optimal insulation structure. The optimal results are PMMA/PVP/PMMA as the dielectric layer, using pentacene as organic semiconductor layer which can realize flexible low voltage high performance OFETs. The device working voltage within 5V, with high mobility of 1.2 cm2/Vs, the threshold voltage is 1.3 V, ON/OFF ratio is 106, which achieved can drive low-voltage equipment. Single layer insulation device with PMMA has the problem of low mobility and instability, after the modification of PVP the devices performance was improved, while the PVP materials brings the problems of hysteresis. Three layers of dielectrics structure, the top of PMMA is hydrophobic insulating layer, insulating layer not only further reduce the roughness also improve the hydrophilicity of insulation problem, prevent the oxygen and water in air into the semiconductor layer cause the problem of device performance unstable. From the AFM, the surface of three dielectrics is very smooth with non-pinhole, the pentacene grain is the largest which corresponding the high carrier mobility. We respectively test the bias stability, thermal stability and mechanical stability of the devices. The results show that three layers of insulation device has the best bias resistance, under 5V bias effect 1200 s output current with no obvious attenuation, threshold voltage of the device changes before and after applying bias is only 0.07 V. To test the thermal stability of the device, heat temperature from 20℃ to 120℃, each temperature heat for 2 hours ensure the sufficient heat for the device. The experimental results show that three dielectrics layers device can withstand the high temperature of 100℃ for 2 hours and still has a good device performance at high temperatures, for heating the change of the electrical properties of a detailed analysis, and proposed the corresponding mechanism explains the experimental phenomena. Mechanical stability tests respectively adopt different ways of bending, vertical channel and parallel channel under the different bending maintain state let stand for 2 hours and other tests. Experiments show that the device in 1000 consecutive mechanical bending state, parallel to the vertical channel or channel bend performance basic stable, bending remain in a state of rest for 2 hours later, the threshold voltage variation within the 0.5 V, the device show good low voltage operation and operation stability. We research the three dielectrics layer flexible low voltage OFETs with good electrical performance and stability, the research provides a new method of the flexible low-voltage memory devices.