Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.604202
Title: Characterization and modelling of organic thin film transistors
Author: Hong, Y.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2007
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Abstract:
This dissertation addresses, through experiments and modelling, three important aspects of organic thin-film transistor (OTFT) device physics, namely: mechanisms of gate dielectric bias stress instabilities; correlation of transfer characteristics and pseudogap density of states of the organic semiconductor; mechanisms of source and drain contact resistance. Bias stress effects were investigated for two organic insulators (OI), PVP and PMMA, by employing a Si-SiO2-OI-metal capacitor structures. In the cross-linked poly(-vinylphenol) (PVP), it is found that the bias stress effect results from the motion of ionic impurities due to the presence of remnant water. A drift diffusion model is used to describe the ion transport and the resulting bias stress effect. In poly (methyl methacrylate) (PMMA), the physical origin of bias stress effect is twofold. In short time scale, β dielectric relaxation causes a big step of flat-band shift upon the change of bias polarity. Over long time scale, hole injection from the top electrode into PMMA causes nonsaturated flat-band shift which follows the diffusion-limited thermionic emission theory. Next, the author has studied the temperature dependence of transfer characteristic of poly (9,9-dioctylfluorene-co-bithiophene) (F8T2) TFT. A model based on an exponential distribution of density of states (DOS) above a conduction level is formulated and shows a good agreement with experimental gate voltage and temperature dependence of the channel current. The method allows to estimate the trap density and correlate it with the TFT fabrication conditions. Finally, the author has examined the contact effects in Au electrode bottom-contact pentacene TFT. Combination of 2-D modelling and experiments indicates that the poor contact is due to the injection barrier between the source contact and channel. The current-voltage characteristics of the source contact are extracted from the output characteristics.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.604202  DOI: Not available
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