Solution Processed Metal-Oxides for Thin Film Applications

Antoniou, Giorgos and Adamopoulos, George (2024) Solution Processed Metal-Oxides for Thin Film Applications. PhD thesis, Lancaster University.

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Abstract

Transparent electronics is a new technology that troubled scientists the recent years and focuses on designing and implementing invisible to the eye circuitry. Metal oxides constitute the best candidates due to their high optical transparency and excellent electrical characteristics. One can easily say that is the most important discovery in the field during the last years, enabling transparent electronic technology to evolve even more and is expected to dominate the post-silicon era. This thesis focuses on the investigation of structural, morphological and electrical properties of different metal oxides and their implementation in TFTs. Spray pyrolysis was used for the fabrication of those metal oxides, a low-cost, large-scale technique. The dielectric properties of zirconium oxide doped with yttrium oxide nanoparticles were investigated, exhibiting high dielectric constant (27), wide optical band gap (5.85 eV) and low current leakages (0.3 nA/cm2). Zirconium oxide was doped with different amounts of yttrium oxide, fully stabilising it at a cubic structure at an yttrium concentration of 5 mol %. Solution-processed In2O3-based TFTs were fabricated, showing excellent TFT characteristics, i.e. high electron mobility (38 cm2/Vs), very low threshold voltage (0.3 V) and large on/off ratio (107). Furthermore, the stability of spray coated In2O3 doped with tungsten TFTs was investigated, employing equally spray coated yttrium oxide gate dielectrics. In2O3 doped tungsten MOSFETs had practically no effect on the band gap, but the Urbach tail energy increased up at higher W content. In addition, at increased W amount, the TFT performance is decreased. At In2O3:W 0.1 at %, the TFT stability is significantly improved, compared to the un-doped ones. This can be determined by the insignificant change of the subthreshold swing, threshold voltage and electron mobilities. ii | P a g e Lastly, the ferroelectric properties of Bismuth Ferrite were investigated. Hysteresis loops due to polarisation were investigated for the bismuth ferrite films, exhibiting remanent polarisation of 60 μC/cm2 and a distorted hysteresis loop due to high current leakages of the film. Aluminium oxide films were spray coated on the bismuth ferrite films to compensate for the high current leakage. Hysteresis due to polarisation was saturated, increasing the remanet polarisation to 170 μC/cm2.