The Performances Of Field Effect Transistors Based On Metamaterials

Metamaterials are artificial materials in a sense, which does not exist in nature, aredesigned and controlled artificially, with the special performances. Their nature and functionsdepend on their internal structures primarily rather than the materials themselves. With thedevelopment of materials technology, the concept of materials has been changed from rawmaterials previously into materials, in which the structures were controlled on a certainpresently. Poly（3- hexyl polythiophene） （P3HT） is a excellent organic semiconductor material,the AIBN was added in the solution of P3HT to modify the P3HT and improve itsperformance. The semiconductor materials such as single-walled carbon nanotubes （SWNT）which has tubular structure and molybdenum disulfide （MoS2） which has layered structure,we separated the SWNT and exfoliated the MoS2repectively to abtain the metamaterials inwhich the structure was changed as we expected. We study the three materials and apply theminto the fabrications of FETs in our work:（1） Poly（3- hexyl polythiophene） （P3HT） is a traditional organic semiconductor materialwith high mobility and good stability. We can modify the P3HT and change its structure. Weadded the free radical initiator azodiisobutyronitrile （AIBN） into the P3HT with certainconcentration, the P3HT with AIBN device exhibited a better field effect characteristiccompared to that of the P3HT without AIBN device. The current on/off ratio （Ion/off） wasincreased from 1.5×101to 1.56×10², the mobility was increased from 0.002 cm²/Vs to 0.04cm²/Vs in the same device. The effect of AIBN reduce the P3HT film surface roughness andmake the film smoother for the carrier to transmit, improving the performance of the device.（2） The single-walled carbon nanotubes （SWNTs） are mixed by tubes with differentchiralities which mainly consists of conducting nanotubes （m-SWNTs） and semiconductingnanotubes （s-SWNTs）. A selective removal of the m-SWNTs with small diameters from theSWNTs by using HNO3/H2SO4mixed solution has been adopted. Moreover, as a proof totestify the separation result, the OFETs were fabricated based on the P3HT, untreated SWNTsand s-SWNTs mixed with P3HT, respectively. From the analysis of devices outputperformance, it could be found that the P3HT/SWNTs device did not present any field effectcharacteristic, but the P3HT/s-SWNTs device exhibited a better field effect characteristiccompared to that of the P3HT device in which the P3HT acted as a bridge. The current on/offratio （Ion/off） was increased from 1.38×10²to 5.52×10², the threshold voltage （Vt） was alsoincreased from -28V to -22V and the mobility was increased from 3×10^-3cm²/Vs to 5×10^-3cm²/Vs in the same device.（3） Inorganic graphene analogues （IGAs） such as MoS2have been attracting rapidlyincreasing attention in recent years with a sandwich structure. The layers loosely bound toeach other via weak van der Waals while the interactions combine with strong covalent.Bulk MoS2is a semiconducting material with an indirect bandgap while single-layer MoS2is a direct gap semiconducting material with high mobility. Intercalation and exfoliation ofMoS2were done in two steps. We characterized the properties of single-layered MoS2byXRD, TEM and SEM. As a proof of concept, a single-layered MoS2-based FET device isfabricated, The current on/off ratio （Ion/off） was 3.2×10³cm²/Vs and the mobility was 4.65cm²/Vs.