| In recent years, OFET (organic field-effect transistor) has received widespreadattention because of the characteristics of simple process, low manufacturing cost,low manufacturing temperature and feasibility to be large area production with goodflexibility. At present, OFET has made great progress in performance, but it hasmany challenges to be uesed in flexible display driver and the organic integratedcircuits. The contact resistance between metal electrode and the organicsemiconductor is a key factor affecting the performance of the device. Relatedresearch shows that inserting an appropriate modified layer between the metalelectrode and the organic semiconductor can improve the interface contact qualityeffectively, and then improve the performance of the device.Firstly, an introduction of the development of OFET, research status andproblems encountered is presented in this artical. Afterwards, according to theoperating principle of a field effect transistor，the influence of electrode modificationon the performance of OFET is elucidated. Then, EuF3(Europium Fluoride) hasbeen used as the modified layer for source and drain electrodes, and its effect on theperformance of OFET is studied. The specific work and results are as follows:(1)The OFET based on CuPc was fabricated, which used the low work functionmetal Ag with EuF3modified layer to be the source and drain electrodes. The performances of the OFETs with different thicknesses of modification layer werestudied. At the same time, the contact resistancet was obtained by means of thepreparation of similar device with five kinds of different channel lengths. Resultsshowed that the contact resistance was reduced from23.65×105Ω·cm to3.86×105Ω·cm as the thickness of EuF3increased from0nm to0.6nm, which lead toan increased field-effect mobility from1.5×10-3cm2/V·s to4.65×10-3cm2/V·s. TheUPS results showed that an interfacial dipole potential was formed between thesilver electrodes and the organic semiconductor layer, which raised the surface workfunction of the source and drain electrodes and reduced the hole injection barrier,thus decreased the contact resistance and improved the hole injection efficiency.(2)The OFET based on Pentacene was also fabricated, and used the EuF3filmas a modified layer for low work function metal Ag source and drain electrodes. Theperformance of device gets the best when the thickness of EuF3modified layer is0.6nm, compared to the unmodified device, it has a six and half fold increase in thehole mobility. The results confirmed the mechanization again：an interfacial dipolepotential is formed between the silver electrodes and the organic semiconductorlayer, which raised the surface work function of the source and drain electrodes andreduced the hole injection barrier, thus improved the performance on devices.(3)The OFET based on PTCDI-C13was fabricated prepared by inserted anEuF3thin layer between metal Ag source drain electrodes and active layer.Experimental results showed that the electron mobility decreases rapidly byincreasing the thickness of EuF3layer, and when its thickness increased to0.9nm,the device has no effect current. It could be illustrated with the conclusion above, aninterfacial dipole potential is formed between the silver electrodes and the organicsemiconductor layer, which raised the surface work function of the source and drainelectrodes and enlarge the electron injection barrier, thus decreased the hole mobility,increased the threshold voltage, Influenced the performance of OFET.To summary, compared to noble metal Au, using an ultra-thin film of EuF3as amodified layer for low work function metal Ag source and drain electrodes can improve the interface quality and the hole mobility effectively, which caused anenhancement of the performance on P type OFET device. It has the profoundsignificance to reduce manufacturing cost and enhance the practical value. |
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