Basic Research On Electrical Contact Based On Ti And Ni In Organic Field-effect Transistor

In recent years,organic electronics has attracted great interest for its unique features like large are,flexible,environmentally friendly,and low cost.With the extensive research,as the fundamental building block of many applications,organic field-effect transistor(OFET)has demonstrated amazing potential in a variety of applications such as flexible displays and sensors.However,due to the lack of suitable doping approach for organic semiconductor,it is difficult to make good ohimic contact between the contact electrodes and the organic semiconductor.This limits the efficiency of charge injection,in particular for N-type OFETs,and thus leds to high contact resistance seriously hindering further development.Upon the above context,this thesis takes titanium metal(Ti)and nickle(Ni)as examples to study the electrical contacts of N-type OFETs.The content is described as follows:(1)Using Ti,Ni and gold(Au)as contact electrodes,N-type OFETs with top-gate,bottomcontact structure were prepared by solution process.Then,we performed electrical characterizations and and investigated the underlying mechanism.Our experimental results showed that,compared with the counparts with Au contact,the N-type OFETs using Ti or Ni as the source and drain electrodes not only effectively reduced the fabrication cost but also improved the contact properties.The contact resistance was reduced,effectively improving the relevant device performance.(2)Taking Ti and Ni as examples,the influence of the contact electrode’s thicknesses on N-type OFETs with top-gate,bottom-contact strcutures was studied.The devices were prepared by despositing Ti and Ni at different thicknesses,and then the corresponding electrical characterizations were carried out.Our experimental results showed that,for top-gate,bottom-contact device,the best performance was observed as the contact electrode’s thickness was 50 nm.Besides,as the thickness of the electrode increased,the morphology of the semiconductor film was affected by the electrode,and the contact properties degraded.(3)Taking Ti,Ni and Au as examples,the influence of contact electrodes on the environmental stability of N-type polymer OFETs was studied.Our experimental results showed that water and oxygen in air were the key factors responsible for device degradation,among which the Ni-contacted devices showed the best air stability and could maintain stable,unipolar electrical characteristics.For Au-contact OFET,in contrast,exhibited very poor air stability and the bipolar electrical characteristics became more pronounced upon exposure to air.Besides,although the Ti-contacted devices maintained stable unipolar electrical characteristics,they were extremely unstable in air;after5 days of air exposure,the devices almost could not function any more.