Simulation, Synthesis and Characterization of Multi-Phase Functional Materials for Emerging Computing Device Applications

This doctoral dissertation focuses on multi-phase functional materials for the emerging computing hardware application by exploring phase-change materials and multifunctional oxide thin films. Phase-change materials is an important class of multi-phase functional materials that transit between polycrystalline and amorphous phases based on Joule heating. Although they have been widely studied to advance emerging nonvolatile memory technology (e.g., phase-change memory) for many decades, there are several challenges that still need to be overcome. In this work, both simulative and experimental approaches are employed to investigate the effect of dry etching on the nanoscale phase-change memory device performance and to further engineer the physical characteristics of phase-change alloys for adoption in far-reaching high-temperature applications, respectively. Multi-functional oxide thin films and their application in the computing hardware are also studied in this research. Owing to their unique multi-functionalities such as piezoelectricity and memristive switching, perovskite oxides possess the potential to create the low-power, high-performance logic device. It is proposed that piezoelectric and memristive oxide layers can be vertically stacked to create an epitaxial heterostructure, which is key to implement stress-induced conductivity modulation in the channel layer of electrostrictive field-effect transistor. Chapter 1 provides an overview of the state-of-the-art nonvolatile memory and steep-slope devices that can form a useful part of the emerging computing hardware. Chapter 2 presents the finite-element (COMSOL) simulation study on the nanoscale phase-change memory device that employs GST (Ge2Sb2Te5) as the switching layer. In this simulation, two scenarios of dry etching are emulated to provide a guideline on the device manufacturing design. Chapter 3 studies the multi-functional perovskite oxide materials to discuss the novel steep-slope device concept. Chapter 4 investigates a wide range of phase-change materials for high-temperature applications. Finally, Chapter 5 summarizes the key findings of this research on multi-phase functional materials and related computing devices.