Synthesis and characterization of Sol-Gel derived ZnO thin Films for memristive Applications

The sol-gel route is a versatile wet chemistry method suitable for the preparation of multi-layer thin films with defined thickness and surface roughness. In this thesis work, sol-gel derived undoped and doped ZnO multi-layers were prepared by spin coating technique on different substrates for a memristive application. The curing and annealing conditions for the ZnO films were adjusted based on the study performed on the ZnO xerogel powders, and taking into account the thermal stability of the engineered substrate used as a bottom electrode for the fabrication of the memristive building block. Chemical, structural and morphological features of the samples were investigated by complementary techniques including electron microscopy, Fourier transform infrared spectroscopy, micro-Raman, X-ray photoelectron spectroscopy and X-ray diffraction analysis. The combined characterization techniques assessed that uniform, dense and flawless films were obtained on the platinum substrate, i.e. the bottom electrode of the memristive cell. In particular, Al-doping was found to significantly affect the surface morphology, grain sizes and overall porosity of the films. According to the electrical measurements performed on undoped and Al-doped ZnO thin films sandwiched between Pt/Ti/SiO2 bottom electrode and different top electrodes including Ag and Pt-dishes, the selected fabrication conditions were suitable for fulfilling the requirements of active layers for the memristive development. The modification approach exploited toward the improvement of the memristive switching performances resulted in memristive responses with low compliance current in absence of electroforming steps. Furthermore, the resistance values at high resistance and low resistance states were reduced in the case of Al-doped films compared to the results obtained from undoped ZnO thin films.