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Title: Study of diodes and transistors for organic circuits
Author: Prior, Suzanne Michelle
ISNI:       0000 0004 2701 9182
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2009
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In recent times much research has been carried out regarding the use of organic materials to fabricate electronic devices, for example diodes and thin film transistors. This thesis examines the use of polymers and small molecule materials to fabricate these devices with the aim of developing a greater understanding of their operation and to provide the basis for the development of circuits. Various materials are used to fabricate Schottky diodes and the measurements enable them to be compared. Equations are developed to describe the operation of the diodes and to facilitate the modelling of circuits. Schottky diode characteristics were also studied at various temperatures. This is important since many of the materials do not conduct heat very readily and the effect of internal heating may be important. Temperature measurements also provide useful evidence of the nature of the conduction process and demonstrate the validity of the analytical work. Such models often, unintentionally, have temperature as one of the variables. Capacitance measurements were obtained for the Schottky diodes to establish how the depletion region width alters with frequency, applied voltage and doping. A series of expressions were also derived to establish the theoretical relationships between the parameters and these were checked against experimental results. The transient response of the diodes was also modelled and compared to experimental results. This was carried out at both a uniform temperature and at varying temperatures.The final chapter of the thesis moves onto polycrystalline materials as opposed to polymers. The reason for this was the higher carrier mobility. It is practically important to have a single set of equations for both disordered and polycrystalline material if they are to be modelled in design software. This part of the project was to establish how the different transport mechanisms compare and also how parameters such as Tc vary between different kinds of material. The polycrystalline experiments were completed using TFTs because diodes fabricated with polycrystalline material were not available at the time. Having completed this work it is apparent that further work could be undertaken to aid the analytical aspects of the subject. Polycrystalline diodes need to be studied and compared with disordered diodes. Assessment of the potential value of the two types, for circuit applications, is essential, particularly from the point of view of circuit performance and cost. This implies an extension of the work to flexible substrates. It would also be of use to fabricate the devices in more ideal conditions to eliminate the effects of air. A wider range of temperatures should also be used to establish how internal heating of the devices affects the results. The effect of temperature on device capacitance and measurements under pulsed inputs would go someway to describing the mechanisms involved with digital circuits.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available