Resistive Switching Characteristics of Metal Oxide Nanostructures Based on Surface Effects and Its Application to Emerging Memory Device

Abstract

Memory is a device capable of storing and processing information. Today, conventional charge–based semiconductor memories represent computing properties based on charge trapping/detrapping phenomena. As a new memory technology, resistance memories usually rely on their distinctive high or low resistance states as the binary numbers ‘0’ and ‘1’. Since resistance is changed under application of an electrical stimulus, resistance switching memory also have been widely referred to as resistance switching RAM (ReRAM). As its lexical–semantic, until now, resistive switching phenomena usually rely on repeated electrical switching between non–volatile resistance states in an active material under the application of an electrical stimulus. To escape from the common device performance from limited controlling conditions, recent reports have explored the use of a variety of external operating parameters. In this study, as a new impetus, photon toward the electronic device is supposed to operate the resistive switching behavior and provides reliable performances. In chapter 2, to demonstrate the switch involved in an optical modulation, point defects are suggested to be an intimately connecting factor that would be influenced by optical phenomena and influences on resistive switching process. The existence of abundant surface or interface states play a crucial role in resistive switching processes by migration, oxidation and reduction via thermochemical reaction. And the surface defects also exhibit oxygen adsorption and photo–desorption property generated by capturing free electrons to from chemisorbed oxygen species From this reasons, 1D nanorods metal oxide is considered to be an effectual system to provide their resistive switching properties as a function of geometric dimensionality and surface effects. In chapter 3, 1 dimensional ZnO nanorod array is utilized to compare the resistive switching behavior in light and dark conditions. In dark condition, the difference between the two resistance states under dark conditions was relatively negligible, and only one resistance state was observed. In contrast, under illumination conditions, the bi–level resistance states of the device could be switched by opposite voltage polarities. SET and RESET voltages were measured about –1.3 V and 1.3 V, respectively, indicating that the device can be operated below 2 V. The filament–based LRS mechanism was proposed by analysis of the current (I)–voltage (V) curve fits of the data, which displayed typical Ohmic conduction. And for HRS, the conduction behavior agreed qualitatively with the trap–associated space charge limited conduction (SCLC) theory. In chapter 4, the reliable light incident angle selective resistive switching performances is provided using the association between wave characteristics of photons and 2–medium structure which is derived from superhydrophobic surface treatment. Typical resistive switching characteristics were observed upon irradiation by particular incident angle smaller than critical angle, in sharp contrast with the results obtained from a device operated with larger than critical angle. Underlying mechanism in the context of illumination angle selectivity was proposed on the basis of the fact that the chemisorbed oxygen readily affect to the formation and dissipation of conductive filament. Furthermore, to test the ambient effects on resistive switching and prove the proposed mechanism, anaerobically designed experiment was proceeded with passivation layer. With a liquid passivation layer, stable and reversible exchange was achieved between the ReRAM and WORM type characteristics, by tailoring the ambient conditions of ZnO nanorod surface. In chapter 5, within a convex curvature, the rotating or bending angle selective prototype memory cell was demonstrated with the organic–inorganic combined structure, e.g. PDMS/PDMS spacers over Au/ZnO nanowire/Au coated Polyimide system. The association of the metal oxide nanorod and polymer, which enables exclusive response with appropriate directional motion of itself to the fixed light direction. This device architecture provides advantages to interfacial property through influencing the energy band near interface so that access time has a chance to be progressed. The polymer covered type will be a more suitable structure for achieving improved endurance or retention data than that of the system in the water.