Large-area flexible electronics based on low-temperature solution-processed oxide semiconductors

Due to their high charge carrier mobility, optical transparency and mechanical flexibility, thin-film transistors (TFTs) based on metal oxide semiconductors represent an emerging technology that offers the potential to revolutionise the next-generations of large-area electronics. This thesis focuses on the development of high-performance TFTs based on low-temperature, solution-processed metal oxide semiconductors that are compatible with inexpensive flexible plastic substrates. The first part of the dissertation describes an ultraviolet light assisted processing method suitable for room-temperature activation of ZnO nanoparticles and their application as semiconducting channels in TFTs. The impact of the semiconductor/dielectric interface on electrical performance is studied using different device configurations and dielectric surface-passivation methods. Furthermore, a nanocomposite concept is proposed in order to assist electron transport between different crystalline domains. Using this approach, TFTs with electron mobilities of ~3 cm2/Vs are demonstrated. The second part of this work explores a carbon-free, aqueous-based Zn-ammine complex route for the synthesis of polycrystalline ZnO thin-films at low temperature and their subsequent use in TFTs. Concurrently, the development of a complementary high-κ oxide dielectric system enables the demonstration of high-performance ZnO TFTs with electron mobilities >10 cm2/Vs and operation voltage down to ~1.2 V. This low-temperature aqueous chemistry is further explored using a facile n-type doping approach. Enhancement in electrical performance is attributed to the different crystallographic properties of the Al-doped ZnO layers. The final part of the thesis introduces a novel TFT concept that exploits the enhanced electron transport properties of low-dimensional polycrystalline quasi-superlattices (QSLs), consisting of sequentially spin-cast layers of In2O3, Ga2O3 and ZnO deposited at temperatures 40 cm2/Vs - an order of magnitude higher than devices based on single binary oxide layers. Based on temperature dependent electron transport and capacitance-voltage measurements, it is reasoned that the enhanced electrical performance arises from the presence of quasi two-dimensional electron gas-like systems formed at the carefully engineered oxide heterointerfaces buried within the QSLs.Open Acces

An Application of the Moving Frame Method to Integral Geometry in the Heisenberg Group

We show the fundamental theorems of curves and surfaces in the 3-dimensional Heisenberg group and find a complete set of invariants for curves and surfaces respectively. The proofs are based on Cartan's method of moving frames and Lie group theory. As an application of the main theorems, a Crofton-type formula is proved in terms of p-area which naturally arises from the variation of volume. The application makes a connection between CR geometry and integral geometry