Walker, D E. (2013)
Improving Performance in Metal Oxide Field-effect Transistors.
Technische Universität Darmstadt
Ph.D. Thesis, Primary publication
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Item Type: | Ph.D. Thesis | ||||
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Type of entry: | Primary publication | ||||
Title: | Improving Performance in Metal Oxide Field-effect Transistors | ||||
Language: | English | ||||
Referees: | von Seggern, Prof. Heinz | ||||
Date: | 21 June 2013 | ||||
Place of Publication: | Darmstadt | ||||
Journal or Publication Title: | Improving Performance in Metal Oxide Field-effect Transistors | ||||
Date of oral examination: | 21 June 2013 | ||||
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 | ||||
Additional Information: | Date of Submission: 19.04.2013 Date of Exam: 21.06.2013 |
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Classification DDC: | 500 Science and mathematics > 500 Science 500 Science and mathematics > 530 Physics 600 Technology, medicine, applied sciences > 620 Engineering and machine engineering |
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Divisions: | 11 Department of Materials and Earth Sciences > Material Science > Electronic Materials | ||||
Date Deposited: | 18 Dec 2013 09:53 | ||||
Last Modified: | 09 Jul 2020 00:31 | ||||
URI: | https://tuprints.ulb.tu-darmstadt.de/id/eprint/3596 | ||||
PPN: | 386312028 | ||||
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