Study On The Surface Modiifcation Of Organic Field-effect Transistors

With the rapid development of information technology, displays, electronic paper,RF trademarks and other products have been into people’s vision. Remarkabledevelopment of the transistors has been achieved since the past half century. Duringsupermarket shopping, without having to queue, the total amount of the cost can bequickly displayed only by pushing a shopping cart directly and walking through thedetector; collapsible displays could be folded at any angle, which greatly saves space;miniaturized smart phones do carry easily; these wonderful scenes indicate that thetransistors are facing another revolution: organic field-effect transistors （OFET）transit from the traditional inorganic semiconductor transistors. The biggest differencebetween inorganic field-effect transistors and organic field-effect transistors is that theorganic transistors adopt organic semiconductors as the active layer material.Compared with inorganic field-effect transistors, organic transistors show prominentadvantages, and the research on the OFET is in full swing. The latest explorationabout the novel organic semiconductor materials has made rapid progress. However,relatively speaking, there is only a little bit the research in terms of the interfacialproperties of OFET. Therefore, this article is mainly focused on the study of theimpact of the OFET insulating layer, that is to say, the interface modification, on thedevice performance. Specific studies are as follows:First, the article briefly described the progress and the significance of the research,the OFET applications and current research hotspots. The device structures, theorganic semiconductor materials, the electrode materials, and the insulating layermaterials were summarized. Then, the basic working principle of the OFET wasintroduced. The conductivity type of the organic semiconductor, the electrical modeland corresponding main parameters of the OFET were expounded further. Moreover,semiconductor growth theory, the effect of the surface energy and the roughness ofthe insulation layer on the device performance were exhibited, which was used for thetheoretical basis of the experiment.Then, we fabricated high-performance OFET devices and the effect of the OTS-modified layer on the device performance was studied. Experimental resultsshowed that the modification with OTS resulted in a higher degree of ordering of theorganic semiconductor thin film, and flatter surface morphology, and thus the mobilityrate increased a lot. The superior insulating properties of OTS layer lead to theincrease of the switching ratio by about three orders of magnitude. We also had depthstudy of the influence of the fast annealing way on the OFET performance, and foundthat quality of the pentacene thin film could be greatly improved by adopting fast wayof annealing, and fast annealing method would further reduce surface trap density, sothe mobility increased, while the threshold voltage decreased.We also selected three polymers （PMMA, PS, PVP） to modify SiO₂insulatinglayer. The experimental results showed that after the modification by polymers,orderly and surface morphology of the organic semiconductor thin film had not beensignificantly improved, so we calculated the maximum trap density of variousinsulating layer, which presented that maximum trap densities were reduced bypolymer modification, and thus the mobility increased a lot. Polymers’ superiorinsulation also made the on/off rations raise up to about106. Furthermore, fastannealing method was possible to obtain the highest degree of order and lowestroughness, and therefore the pentacene film properties could be further optimized. So,fast annealing method was possible to further reduce the density of the surface trap,decrease the threshold voltage, and finally improve mobility. Meanwhile, from theaspect of the dipole electric field, the analysis about the reason why PVP modifiedlayer obtained OFET lowest threshold voltage was conducted. It was speculated thePVP dipole electric field generated a surface potential, whose effect was equivalent toapply a negative gate voltage to the gate, so the threshold voltage decreased.Finally, we summarized this paper work, and, combining with the current researchprogress discussed the OFET development trends and prospects.