| The focus of this research is on integrating redox-active, organic molecules into Si-based structures to first, characterize and understand the properties of molecules; second, generate a new class of hybrid silicon/molecular devices for memory applications; and third, open a new way to develop molecular-only devices. The approach of hybrid silicon/molecular electronics is to provide a smooth transition technology by integrating molecular intrinsic scalability and properties with the vast infrastructure of traditional MOS technology. This dissertation has concentrated on the fabrication, characterization and modeling of hybrid silicon-molecular devices for memory applications.; First, specific procedures have been successfully developed for attaching redox-active, tightly-bonded, well-packed, molecular self-assembled monolayers on Si and SiO2 surfaces. The molecules can be attached on the surfaces through solution-phase or vapor-phase deposition. The molecular monolayers attached on Si and SiO2 surfaces via covalent C-O-Si bonds exhibit stable performance during electrical characterization in a well-controlled, inert environment. Molecular multilayer films have been also deposited on Si surface with very high surface coverage.; Second, an electrolyte/molecule/Si structure has been implemented for electrical characterizations to understand the molecules and their application in memory devices. The electrical characterizations include traditional cyclic voltammetry, capacitance voltage/conductance-voltage measurements, impedance spectroscopy, and MOSFET/DRAM write/erase I-V measurements.{09}A specific model based on Maxwell's equations was developed to describe and understand the kinetics of charge transport and current-voltage characteristics of the molecular capacitors. Equivalent RC circuits have been developed to understand the characterization of impedance spectroscopy and extract RC coefficients for electrolyte, molecule and Si of this structure. In addition, a possible application of electrolyte/molecule/Si capacitors in DRAM has been presented and explored.; Third, two different strategies to achieve multibit memory have been developed and optimized using the methods of attaching mixed monolayers and stacked multilayer films. Multiple redox states at well-separated, discrete gate voltages have been obtained from mixed monolayers and stacked multilayer films, which augments the advantages for memory application.; Fourth, molecular multilayer films with very high surface coverage have been achieved for application in memory devices. Metal/molecule/Si sandwich structures using molecular multilayer films were fabricated and exhibited nonvolatile electrical switching properties. A set of control experiments indicate that these switching properties are due to the interaction of metal/molecule interface instead of the redox-related processes.; In conclusion, this thesis has focused on hybrid silicon/molecular electronics and has investigated the intrinsic properties of molecules and proposed feasible ways to apply molecules in memory devices. This dissertation indicates that hybrid silicon/molecular technology may provide a smooth transition from microelectronics depending on properties of bulk materials to nanoscale electronics with molecule as the key component in circuitry. |
