Abstract
In this thesis, we focus on improvement of ZnO-based resistive random access memory (RRAM) researches. ZnO was a main material prepared by the atomic-layer-deposition (ALD) and magnetic sputtering technique for RAM devices. In the first part, inductively coupled plasma technique (ICP), namely, remote-plasma treatment was used to ionize the water molecules in order to improve the deposition of ZnO film via the atomic layer deposition processes. The relationship between resistivity and formation mechanisms have been discussed and investigated through analyses of atomic force microscopy, photonluminescence, and absorption spectra, respectively. Findings indicate that the steric hindrance of the ligands plays an important rule for the ALD-ZnO film sample with the ICP treatment while the limited number of bonding sites will be dominant for the ALD-ZnO film without the ICP treatment owing to a decrease of the reactive sites via the ligand-exchange reaction during the dissociation process. Finally, the enhanced aspect-ratio into the anodic aluminum oxide with the better improved uniform coating of ZnO layer after the ICP treatment was demonstrated, providing an important information for a promising application in electronics based on ZnO ALD films. In the second part, a stability scheme of resistive switching devices based on ZnO films deposited by radio frequency (RF) sputtering at different oxygen pressure ratios. I-V measurements and statistical results indicate that operating stability of ZnO ReRAM devices is highly dependent of the oxygen conditions. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) of ZnO at different O2 pressure ratios were investigated to reflect influence of structure to the stable switching behaviours. In addition, PL and XPS results were measured to investigate different charge states triggered in ZnO by oxygen vacancies, which affect the stability of the switching behavior. In the final part, we combined the concept of the first and the second research to fabricate a bi-layer structure ZnO RRAM device. A non-linear behavior was observed in a small operating condition region. The results should be the solution to solve the sneak path problem in the cross-bar array RRAM application.