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Etude des transistors à effet de champ organiques : réalisation d'OFETs ambipolaires et étude des mécanismes d'injection dans les OFETs verticaux

Abstract : Organic Field Effect Transistors (OFETs) is increasingly attractive thanks to the possibility of producing lighter components at lower cost and on flexible substrates. Being able to couple a light emission function to a transistor function makes its use more interesting. This is the case with display applications, where the pixels are produced by an active matrix technology of organic light-emitting diodes (AMOLED). Having a light-emitting OFET makes possible to combine an OFET with an organic light-emitting diode (OLED) and thus simplifying the design, the manufacturing steps as well as increasing the lifetime of pixels. During this thesis, the study and manufacture of light-emitting OFETs were carried out using two approaches. The first one is based on the study of ambipolar OFETs based on N, N'-ditridecyl-3,4,9,10-perylenetetracarboxylic diimide (PTCDI-C13), an n-type semiconductor, and pentacene, a p-type semiconductor. This study constitutes the first step in obtaining electroluminescent OFETs. The fabrication and characterization of these ambipolar OFETs were performed for the first time in the laboratory's research team. A study of their structure was carried out to find the ideal parameters to obtain a balanced charge transport. The optimized structure is a bilayer structure with a pentacene thickness of 8 nm and a PTCDI-C13 thickness of 20 nm. The addition of an emitting layer between the two semiconductors failed to achieve light emission due to excessive charges trapping. However, this study has opened up new perspectives for future work on ambipolar OFETs. The second approach to study light-emitting OFETs is more innovative thanks to the change of the structure from a classic planar structure to a vertical one. This structure has the advantage of being able to easily integrate an OLED structure and has a homogeneous light emission over a large area. The operating principle is totally different from conventional OFETs: here, the current modulation is no longer done by controlling the conductivity in a semiconductor channel, but by controlling the injection of charges at the source electrode. The study of this structure made it possible to obtain luminous organic transistors. Then, the study of charge injection mechanisms allowed us to understand more deeply the operating principe of these transistors. Several materials have been tested as the source electrode: gold, silver, aluminum and ITO (Indium Tin Oxide). This study allowed us to determine the injection mechanism involved, namely the injection of charges by the modulation of the tunnel effect thanks to the band bending induced by the gate effect in the semiconductor layer close to the interface. It has also been identified that the quality of the source electrode/semiconductor interface plays a major role since poor interface quality leads to a drastic decrease in performance.
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Marjorie Morvan. Etude des transistors à effet de champ organiques : réalisation d'OFETs ambipolaires et étude des mécanismes d'injection dans les OFETs verticaux. Micro et nanotechnologies/Microélectronique. Université Paul Sabatier - Toulouse III, 2020. Français. ⟨NNT : 2020TOU30175⟩. ⟨tel-03184818⟩

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