Basic Research On Electrical Contacts Based On Rare Earth Metals

In recent years,organic field effect transistor(OFET)have attracted extensive attention owing to their excellent flexibility,simple process,low cost and the fact that they can be fabricated at relatively low temperatures.Although OFET has made great progress in performance,it still faces many challenges in large-scale applications such as flexible display drivers and organic integrated circuits.The contact resistance caused by the interface between metal electrodes and organic semiconductors is one of the most important factors affecting device performance.Due to the lack of suitable contact electrodes,it is difficult to form good Ohm contact between electrodes and organic semiconductors,especially the low efficiency of electron injection for N-type OFET,leading to high contact resistance and poor stability and thus severely limiting its further development for large-scale applications.Based on the above background,this paper briefly introduces the research background and the significance of organic field-effect transistors,the current research situation,application prospect,physical basis,etc.,and selects scandium(Sc),a rare earth metal,as the main research object to study the electrical contact of N-type OFET.(1)Using scandium(Sc)and Au(Au)as contact electrodes,the effects of different materials on electrical properties of top-gate,bottom-contact OFETs were studied.The N-type OFET was prepared by means of a series of tests and analysis of electrical properties and the working mechanism behind it was studied.Compared with traditional Au electrode,using rare earth metal Sc as the source and drain electrodes for N-type OFET can not only reduce the cost but also improve the electrical contact,thus reducing the contact resistance and improving the device performance.(2)The effect of different electrode thicknesses on top-gate,bottom-contact OFETs was studied.By adjusting the thickness of Sc contact electrode,the N-type OFET was prepared by magnetron sputtering and electron beam evaporation,and its electrical properties were systematically tested and analyzed.The experimental results show that the optimum device performance can be obtained when electrode thickness is 50 nm,regardless of the electrode deposition method.In addition,as electrode thickness increases or decreases from 50 nm,the electrical contact performance of the device starts to decline.(3)To study the effect of different electrode deposition methods on device performance.The Ntype OFET was prepared by magnetron sputtering and electron beam evaporation,respectively,and its electrical properties were tested.According to the experimental results,there is a significant difference between the two methods: magnetron sputtering can optimize metal-semiconductor contact and improve the effect of charge injection and subsequently the charge transport.However,compared with electron beam evaporation,the device has obvious disadvantage in terms of mobility,on-off ratio,and threshold voltage.(4)Finally,the effect of annealing of organic semiconductor layer on device performance was investigated under different electrode deposition methods.The experiment used N2200,a commonly used organic semiconductor,to compare rapid annealing at high temperature(200 ° C-20 min)with slow annealing at low temperature(120 ° C-2 h)under the same conditions.It could be concluded that regardless of electrode deposition,when N2200 was annealed at low temperature(120 ° C-2 h),the device performed best in terms of mobility,threshold voltage,subthreshold swing,on-off ratio and contact resistance.