Inorganic p-channel thin-film transistors using CuO nanoparticles

This study focuses on the integration of copper oxide nanoparticles forming inorganic p-channel thin-film transistors (TFTs). The used CuO nanoparticles have a diameter of 25-55 nm and are dispersed in a water-based solution providing the opportunity of low-cost and large-scale integration processes. First investigations were realized using an inverted coplanar TFT architecture due to the low chemical and physical stresses the semiconductor has to withstand. Therefore, a gate electrode consisting of 50 nm aluminum followed by 7 nm titanium was integrated on a Si/SiO2 substrate. As gate dielectric a high-k organic-inorganic nanocomposite was deposited by spin-coating resulting in a layer thickness of 150- 180 nm. For the drain and source electrodes gold and nickel were examined. For both metallizations the influence of an electrode treatment with a self-assembling monolayer (2,3,4,5,6 Pentafluorothiophenol, PFBT) was investigated. The gate metallization as well as the drain/source electrodes were evaporated via e-beam and structured by photolithography followed by wet-etching processes and lift-off technique, respectively. In the last step, the CuO nanoparticle layer was applied by doctor blade process followed by evaporating the solvent in a convection oven under ambient conditions. The maximum temperature during the integration process was 115°C so that a compatibility to glass and foil substrates is given. The influence of the drain/source material on the electrical characteristics was explored as well as the impact of the electrode treatment. Besides single TFTs inorganic inverter circuits in complementary technique were analyzed.