C < Sub > 60 < / Sub > Base Research Of Organic Thin Film Transistor Performance Improvement

Organic thin film transistors （OTFTs） are of great interest owing to theirinexpensive price, light weight and mechanical flexibility for radio-frequencyidentification tags, sensors, and backplanes of active matrix displays. In this thesis,fullerene (C₆₀) was been chosen as active material to fabricate n-channel OTFTs, ourmain purpose is improving device performance and obtaining high field-effect mobility.We modified two interfaces at gate dielectric/semiconductor and source/drain （S/D）electrodes/semiconductor, and based on these modifications we designed a new devicestructure, which obtained high device mobility. Specific work is as following:1. The dielectric/semiconductor interface modification. An ultrathin pentacenebuffer layer was inserted between the polymer dielectric and C₆₀active layer. Devicewith a pentacene buffer layer obtained a mobility of4.22cm²/Vs, which was nearly16times larger than the mobility of corresponding devices without pentacene buffer layer（0.27cm²/Vs）. Atomic force microscopy （AFM） and X-ray diffraction patterns （XRD）were taken to investigate the surface morphology of C₆₀films with and without apentacene buffer layer. Results showed that polycrystalline structure is much moreintense and grain size is larger from C₆₀film with a pentacene buffer layer. Larger grainsize of C₆₀means a smaller number of trap states in the band gap, therefor increase offilm grain size is believed to be the main reason for the improved electron mobilityobtained.2. The electrodes/semiconductor interface modification. High-work-function （WF）stable metal silver （Ag） was chosen as S/D electrodes, but between the Fermi level ofAg and the LUMO level of C₆₀there was a high energy barrier. To improve electroninjection, a LiF buffer layer was inserted between Ag electrodes and C₆₀active layer.The relationship between field-effect mobility and the thickness of the LiF layer wasinvestigated. With an optimal LiF layer thickness of1nm, a field-effect mobility of5.07cm²/Vs was obtained, which was85%higher than that of the corresponding device withsingle Ag electrodes. This can be explained by energy level alignment between S/D electrodes and active layer, and also carrier tunneling by the thin LiF layer.3. New dual-conductible channel structure. C₆₀active layer was been inserted withan electron-blocking layer, which divided one conductible channel into two channels.Field-effect mobility up to6.56cm²/Vs was obtained from an optimizeddual-conductible channel device. AFM was taken to investigate the surface morphologyof upper C₆₀films and we explained the formation of two channels. At last wecontrasted and analyzed device performance after changing thickness and material ofthe electron-blocking layer.