Organic field-effect transistors on novel renewable substrates
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With the increasing awareness of environmental impact from electronic waste and increasing demand for flexible electronic devices, novel substrates with both biodegradability and flexibility have been studied in various fields. To develop such electronic devices, organic electronic technology has attracted attention because of its low process temperature at a range of 60 to 100 °C which is compatible with substrates having these two features. Among organic electronic devices, organic field-effect transistors (OFETs) are an important building block because transistors can implement circuits to integrate with other organic electronic devices such as organic light-emitting diodes (OLEDs) and organic photovoltaics (OPVs). This dissertation reports solution-processed high-performance top-gate OFETs with operational and environmental stability on novel renewable substrates. The first achievement is demonstrating top-gate OFETs with a bilayer CYTOP/Al2O3 gate dielectric on environmentally friendly renewable cellulose nanocrystal (CNC):glycerol substrates. OFETs were fabricated on water soluble CNC:glycerol substrates with a protection layer of Al2O3 by atomic layer deposition. OFETs with that protection layer have better operational and environmental stability compared to that of OFETs on bare CNC:glycerol substrates. The second achievement is reducing contact resistance of top-gate OFETs. By depositing 1.5 nm of Mo(tfd)3 on source/drain electrodes, contact resistance can be 0.25 of that from contact electrodes using the conventional PFBT treatment. The third achievement is developing a nanolaminate structure comprised of Al2O3 and HfO2 to replace Al2O3 in the gate dielectric bilayer in top-gate OFETs to improve their environmental stability while achieving comparable operational stability. OFETs with a modified gate dielectric have comparable electrical properties, operational stability, and environmental stability compared to that of OFETs with CYTOP/Al2O3; furthermore, OFETs with a modified gate dielectric are functioning after storing in hot water at 95 °C for up to 1 h that is much longer than that of OFETs with the original bilayer gate dielectric. The last achievement is presenting top-gate OFETs with modified gate dielectric and reduced contact resistance on cellulose-based paper substrates. OFETs on this type of paper can achieve comparable electrical properties, operational stability, and bending characteristics by the proper choice of a buffer layer coated on top of the paper substrate. In this dissertation, the development of OFETs on novel substrates have been described, and the future study is suggested.