Effect Of The Contact Resistance On The Performance Of Organic Field Effect Transistors

Organic field-effect transistors (OFETs) have received widely attention recently due totheir great advantages such as simple preparation, good flexibility, low cost, suitable for lowtemperature and large-scale manufacturing, and their potential applications in organicelectronics. With the development of OFETs, they have almost reached the performance levelof amorphous silicon. The performance improvement OFETs lead to the wide application inmany fields, such as the flexible display drivers, the smart cards, the identification cards, thedetectors, the electronic packagings, the electronic newspapers and etc. In general, theperformance of OFET was affected by the contact resistance between the source/drainelectrode and organic semiconductor layer. For the improvement and the wider applications ofOFETs device, we modified device performance by inserting metal oxide between electrodesand organic semiconductor layer and improved device performance according to theory model,which is of great significance not only for science but also for practical application.Firstly, this work simply summarized the recent advances and existing problems ofOFETs. Secondly, we introduced various organic materials and common structures in OFETsfabrication. Finally, the carrier injection and transport mechanisms theory were demonstratedin this thesis. Based on the trend and problem of OFETs, we fabricated device with metaloxide buffer layer between small molecule active layer and electrodes and studied theinfluence of contact resistance on the device performance. Moreover, we also investigated thecontact resistance between aluminum and C60or PCBM in OFETs. The specific contents areorganized as follows:(1) The pentacene-based OFETs with thin transition metal oxide (WO3) layer betweenpentacene and source/drain electrodes (Al) were fabricated. The indium tin oxide(ITO) andPMMA functioned as gate electrode and insulating layer respectively. We studied theinfluence of the different WO3layer thicknesses on OFET performance. Compared with thedevices without WO3layer, the insertion of WO3layer result in the interface electric dipolereduction, the injection barrier modification and depinning effect, which contributed to theperformance enhancement of OFETs.(2)The pentacene-based OFETs with thin transition metal oxide (MoO3) layer betweenpentacene and source/drain electrodes (Al) were fabricated. The indium tin oxide(ITO) andPMMA functioned as the gate electrode and insulating layer, respectively. We studied theinfluence of different MoO3layer thicknesses on OFET performance. As a result of electrontunneling effect and energy level match, the insertion of MoO3result in the injection barriermodification, which leads to the performance improventment of OFETs. (3) The OFETs with organic semiconductor material C60and PCBM as active layerwere fabricated. The indium tin oxide(ITO), PVA and Al functioned as the gate electrode,insulating layer and drain/source electrodes respectively. We studied the performance ofPCBM and C60OFETs with different PVA concentrations. In addition, the Maxwell-Wagnermodel was applied to analyze the contact resistance in devices.