Walker, D. E. (2013)
Improving Performance in Metal Oxide Field-effect Transistors.
Technische Universität Darmstadt
Dissertation, Erstveröffentlichung
Kurzbeschreibung (Abstract)
The work described in this thesis is concerned with increasing the mobility of inorganic, solution processed field-effect transistors, fabricated from organo-matallic precursors. Devices were fabricated by depositing the zinc oximate or indium oximate, precursor formulation onto a prefabricated substrate, consisting of a doped silicon gate electrode and silicon dioxide gate dielectric, with gold source and drain electrodes. The formulations used to fabricate the zinc oxide (ZnO) or indium-zinc oxide (IZO) active layers are optimised, for both spin coating and inkjet printing, by changing the solvents according to their Hansen solubility parameters, to result in formulations which give the best mobilities. The thicknesses of the active layers were controlled by varying the precursor concentration in the formulation and found to be a critical parameter, where the mobility of the final layer, rises, peaks, and then decreases as the active layer thickness is increased. This non-intuitive result is examined in detail by direct imaging with scanning probe microscopy techniques and extracting electron density profiles from x-ray reflection measurements. These measurements reveal full thickness variations within the film which are assumed to adversely affect charge transport. Coating additional layers to fill these defects results in a considerable increase in performance. It was found that the optimal single layer thickness was sub-optimal when coating additional layers and by coating many thin layers, films could be created with a density approaching that of bulk IZO and which exhibit a mobility up to 20 cm2/Vs. These results enable a consistent, qualitative model of layer formation to be developed explaining how the morphology of the film develops as the concentration of precursor in the initial formulation is varied. Throughout the work it was found that the environment in which the active layers were created and measured was critical to the final performance. The effects of light, oxygen exposure, electrical stress and temperature on the electrical performance are measured and the effect of oxygen on the source and drain contacts is examined via Kelvin probe force microscopy (KPFM). It is found that oxygen is critical to all aspects of the device performance, however, the effects are always reversible by annealing in the correct atmosphere, oxygen free for ZnO, or air for IZO.
Typ des Eintrags: | Dissertation | ||||
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Erschienen: | 2013 | ||||
Autor(en): | Walker, D. E. | ||||
Art des Eintrags: | Erstveröffentlichung | ||||
Titel: | Improving Performance in Metal Oxide Field-effect Transistors | ||||
Sprache: | Englisch | ||||
Referenten: | von Seggern, Prof. Heinz | ||||
Publikationsjahr: | 21 Juni 2013 | ||||
Titel der Zeitschrift, Zeitung oder Schriftenreihe: | Improving Performance in Metal Oxide Field-effect Transistors | ||||
Datum der mündlichen Prüfung: | 21 Juni 2013 | ||||
URL / URN: | http://tuprints.ulb.tu-darmstadt.de/3596 | ||||
Kurzbeschreibung (Abstract): | The work described in this thesis is concerned with increasing the mobility of inorganic, solution processed field-effect transistors, fabricated from organo-matallic precursors. Devices were fabricated by depositing the zinc oximate or indium oximate, precursor formulation onto a prefabricated substrate, consisting of a doped silicon gate electrode and silicon dioxide gate dielectric, with gold source and drain electrodes. The formulations used to fabricate the zinc oxide (ZnO) or indium-zinc oxide (IZO) active layers are optimised, for both spin coating and inkjet printing, by changing the solvents according to their Hansen solubility parameters, to result in formulations which give the best mobilities. The thicknesses of the active layers were controlled by varying the precursor concentration in the formulation and found to be a critical parameter, where the mobility of the final layer, rises, peaks, and then decreases as the active layer thickness is increased. This non-intuitive result is examined in detail by direct imaging with scanning probe microscopy techniques and extracting electron density profiles from x-ray reflection measurements. These measurements reveal full thickness variations within the film which are assumed to adversely affect charge transport. Coating additional layers to fill these defects results in a considerable increase in performance. It was found that the optimal single layer thickness was sub-optimal when coating additional layers and by coating many thin layers, films could be created with a density approaching that of bulk IZO and which exhibit a mobility up to 20 cm2/Vs. These results enable a consistent, qualitative model of layer formation to be developed explaining how the morphology of the film develops as the concentration of precursor in the initial formulation is varied. Throughout the work it was found that the environment in which the active layers were created and measured was critical to the final performance. The effects of light, oxygen exposure, electrical stress and temperature on the electrical performance are measured and the effect of oxygen on the source and drain contacts is examined via Kelvin probe force microscopy (KPFM). It is found that oxygen is critical to all aspects of the device performance, however, the effects are always reversible by annealing in the correct atmosphere, oxygen free for ZnO, or air for IZO. |
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URN: | urn:nbn:de:tuda-tuprints-35969 | ||||
Zusätzliche Informationen: | Date of Submission: 19.04.2013 Date of Exam: 21.06.2013 |
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Sachgruppe der Dewey Dezimalklassifikatin (DDC): | 500 Naturwissenschaften und Mathematik > 500 Naturwissenschaften 500 Naturwissenschaften und Mathematik > 530 Physik 600 Technik, Medizin, angewandte Wissenschaften > 620 Ingenieurwissenschaften und Maschinenbau |
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Fachbereich(e)/-gebiet(e): | 11 Fachbereich Material- und Geowissenschaften 11 Fachbereich Material- und Geowissenschaften > Materialwissenschaft 11 Fachbereich Material- und Geowissenschaften > Materialwissenschaft > Elektronische Materialeigenschaften |
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Hinterlegungsdatum: | 22 Dez 2013 20:55 | ||||
Letzte Änderung: | 01 Feb 2019 10:05 | ||||
PPN: | |||||
Referenten: | von Seggern, Prof. Heinz | ||||
Datum der mündlichen Prüfung / Verteidigung / mdl. Prüfung: | 21 Juni 2013 | ||||
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