Percorrer por autor "Medeiros, M. C. R."
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- All-inkjet printed organic transistors: Dielectric surface passivation techniques for improved operational stability and lifetimePublication . Gomes, Henrique L.; Medeiros, M. C. R.; Villani, F.; Canudo, J. M.; Loffredo, F.; Miscioscia, R.; Martinez-Domingo, Carme; Ramon, Eloi; Sowade, Enrico; Mitra, K. Y.We report about the use of a printed pentafluorothiophenol layer on top of the dielectric surface as a passivation coating to improve the operational stability of all-ink-jet printed transistors. Transistors with bottom-gate structure were fabricated using cross-linked poly-4-vinylphenol (c-PVP) as dielectric layer and an ink formulation of an amorphous triarylamine polymer as semiconductor. The resulting TFTs had low turn-on voltage (Vth < |5 V|) and a mobility ≈0.1 cm2/(V s). A comparison of identically fabricated transistors shows that devices with coated dielectric have a higher operational stability than those using bare c-PVP. This conclusion is supported by a quantitative study of the threshold voltage shift with time under continuous operation. Long exposure to the ambient atmosphere causes an increase in the threshold voltage strongly dependent on the used semiconducting ink formulation.
- Gate-bias stress in amorphous oxide semiconductors thin-film transistorsPublication . Lopes, M. E.; Gomes, Henrique L.; Medeiros, M. C. R.; Barquinha, P.; Pereira, L. M. C.; Fortunato, E.; Martins, R.; Ferreira, I.A quantitative study of the dynamics of threshold-voltage shifts with time in gallium-indium zinc oxide amorphous thin-film transistors is presented using standard analysis based on the stretched exponential relaxation. For devices using thermal silicon oxide as gate dielectric, the relaxation time is 3 105 s at room temperature with activation energy of 0.68 eV. These transistors approach the stability of the amorphous silicon transistors. The threshold voltage shift is faster after water vapor exposure suggesting that the origin of this instability is charge trapping at residual-water-related trap sites.
- Inkjet-printed organic electronics: Operational stability and reliability issuesPublication . Medeiros, M. C. R.; Martinez Domingo, C.; Ramon, E.; Negrier, A. T.; Sowade, E.; Mitra, K. Y.; Baumann, R. R.; McCulloch, I.; Carrabina, J.; Gomes, Henrique L.The operational stability of all-inkjet printed transistors is reported. At room temperature the threshold voltage shifts following a stretched exponential with a relaxation time τ=1×103 s. Two distinct trap sites active in different temperature ranges, one at 200-250 K and other above 310 K cause the electrical instability. Both types of traps capture holes and can be fast neutralized by photogenerated electrons. Optically induced detrapping currents confirm the differences in trap signature. It is proposed, that the traps have a common physical origin related to water. © The Electrochemical Society.