CuPc Micro/Nano Single-crystal Field-effect Transistors Based On Graphene Bottom Electrodes

Organic field-effect transistors (OFETs) due to the advantages of wide material sources,high integration density, compatible with the flexible substrate and the mass production, sothey have been intensively investigated. The bottom-contact configuration is one of the mainorganic device structures. Bottom electrode structure in the process of electrodes preparationand semiconductors preparation are independent, which avoid the damage in semiconductortechniques such as electron beam lithography, lithography, and suitable for the preparation ofcomplex electrodes and circuits. However, the bottom electrodes are raised on the surface ofthe substrate, when preparing the organic single-crystal devices, the raised electrode stepsmake a poor contact between semiconductor and insulating layer, affect the carriertransmission, and affected the performance of devices. Graphene is a two-dimensional singlelayer of carbon atoms arranged in a cellular structure, which has ultra-thin two-dimensionalsizes, high electrical conductivity and the very good compatibility with organic semiconductor,so the graphene undoubtedly provides a good choice for bottom-contact configuration oforganic field-effect transistors.In this thesis we use the method of the mechanical stripping to prepare the graphene,gold film mask method and oxygen plasma etching method are used to fabricate the gap ofgraphene electrode. And copper phthalocyanine (CuPc) micro/nano single crystals aresynthesized by vapor-phase transport method as the semiconductor. CuPc micro/nano singlecrystal field-effect transistors have been fabricated based on graphene bottom electrodes. Andwe measured the electrical performance of the device. The ultrathin thickness and highelectrical conductivity of the graphene, combined with its good compatibility with organicsemiconductors, produced high-performance CuPc micro/nano single crystal device withmobility at1.186cm2/V s. Due to the CuPc is photosensitive material, current increasesrapidly when it is exposed to visible light. The ratio of the optical current and dark current(ILight/IDark) is103. At the same time the device shows a good optical switch characteristic. Tothe contrast experiment, the Ion/Ioffof the photoswitch is larger than the Au top-electrodeconfiguration. This is due to (1) the very good compatibility between graphene and organicsemiconductor, a low injection barrier between graphene and organic semiconductor, whichfacilitates carrier injection and carrier collection; and (2) the bottom electrode contactstructure near the conducting channel, which facilitates the carrier collection. Top contactstructure is far away from the conducting channel and the carrier through the semiconductortwo times, which not facilitates the collection.