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- Dzwilewski, Andrzej, 1979-
(author)
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Photo-polymerization as a tool for engineering the active material in organic field-effect transistors
- 2009
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Doctoral thesis (other academic/artistic)abstract
- The emergence of organic semiconductors is exciting since it promises to open up for straightforward and low-cost fabrication of a wide range of efficient and novel electronic devices. However, in order for this promise to become reality it is critical that new and functional fabrication techniques are developed. This thesis demonstrates the conceptualization, development, realization and implementation of a particularly straightforward and scalable fabrication process: the photo-induced and resist-free imprint patterning technique.Initial experiments revealed that some members of a group of carbon-cage molecular semiconductors – termed fullerenes – can be photochemically modified into dimeric or polymeric structures during exposure to laser light, and, importantly, that the exposed fullerene material retains its good electron-transport property while its solubility in common organic solvents is drastically lowered. With this information at hand, it was possible to design and create well-defined patterns in a solution-deposited fullerene film by exposing selected film areas to laser light and then developing the entire film in a tuned developer solution. An electronically active fullerene pattern emerges at the locations defined by the incident laser beam, and the patterning technique was successfully utilized for the fabrication of arrays of efficient field-effect transistors.In a later stage, the capacity of the photo-induced and resist-free imprint technique was demonstrated to encompass the fabrication of ubiquitous and useful CMOS circuits. These are based on a combination of p-type and n-type transistors, and a blend between a p-type organic semiconductor and an n-type fullerene compound was designed so that the latter dominated. By solution-depositing the blend film on an array of transistor structures, exposing selected transistors to laser light, and then developing the entire transistor array in a developer solution, it was possible to establish a desired combination of (non-exposed) p-type transistors and (exposed) n-type transistors. We finally utilized this combination of transistors for the fabrication of a CMOS circuit in the form of well a-functional organic inverter stage.
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| 2. |
- Jakobsson, Fredrik Lars Emil, 1974-
(author)
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Charge transport modulation in organic electronic diodes
- 2008
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Doctoral thesis (other academic/artistic)abstract
- Since the discovery of conducting polymers three decades ago the field of organic electronics has evolved rapidly. Organic light emitting diodes have already reached the consumer market, while organic solar cells and transistors are rapidly maturing. One of the great benefits with this class of materials is that they can be processed from solution. This enables several very cheap production methods, such as printing and spin coating, and opens up the possibility to use unconventional substrates, such as flexible plastic foils and paper. Another great benefit is the possibility of tailoring the molecules through carefully controlled synthesis, resulting in a multitude of different functionalities.This thesis reports how charge transport can be altered in solid-state organic electronic devices, with specific focus on memory applications. The first six chapters give a brief review of the field of solid-state organic electronics, with focus on electronic properties, resistance switch mechanisms and systems. Paper 1 and 3 treat Rose Bengal switch devices in detail – how to improve these devices for use in cross-point arrays as well as the origin of the switch effect. Paper 2 investigates how the work function of a conducting polymer can be modified to allow for better electron injection into an organic light emitting diode. The aim of the work in papers 4 and 5 is to understand the behavior of switchable charge trap devices based on blends of photochromic molecules and organic semiconductors. With this in mind, charge transport in the presence of traps is investigated in paper 4 and photochromic molecules is investigated using quantum chemical methods in paper 5.
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| 3. |
- Larsson, Oscar, 1978-
(author)
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Polyelectrolyte-Based Capacitors and Transistors
- 2011
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Doctoral thesis (other academic/artistic)abstract
- Polymers are very attractive materials that can be tailored for specific needs and functionalities. Based on their chemical structure, they can for instance be made electrically insulating or semiconducting with specific mechanical properties. Polymers are often processable from a solution, which enables the use of conventional low-cost and high-volume manufacturing techniques to print electronic devices onto flexible substrates. A multitude of polymer-based electronic and electrochemical devices and sensors have been developed, of which some already has reached the consumer market.This thesis focuses on polarization characteristics in polyelectrolyte-based capacitor structures and their role in sensors, transistors and supercapacitors. The fate of the ions in these capacitor structures, within the polyelectrolyte and at the interfaces between the polyelectrolyte and various electronic conductors (a metal, a semiconducting polymer or a network of carbon nanotubes), is of outermost importance for the device function. The humidity-dependent polarization characteristics in a polyelectrolyte capacitor are used as the sensing probe for wireless readout of a passively operated humidity sensor circuit. This sensor circuit can be integrated into a printable low-cost passive sensor label. By varying the humidity level, limitations and possibilities are identified for polyelectrolyte-gated organic field-effect transistors. Further, the effect of the ionic conductivity is investigated for polyelectrolyte-based supercapacitors. Finally, by using an ordinary electrolyte instead of a polyelectrolyte and a high-surface area (supercapacitor) gate electrode, the device mechanisms proposed for electrolyte-gated organic transistors are unified.
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