Integration of nanostructured titania into microsystems

This thesis describes research on a novel process to fabricate integrated nanostructured titanic (NST) features as functional components in microsystems devices. NST features were formed by oxidizing Ti films in aqueous hydrogen peroxide followed by thermal annealing. The oxidation kinetics and properties of NST formed were investigated. The process developed is compatible with current microelectronics manufacturing practices for Si and plastic substrates.; Amorphous hydrated titanic gels form when hydrogen peroxide (H2 O2) reacts with Ti. Oxidation of a blanket (unpatterned) Ti surface with hydrogen peroxide results in a titanic layer with high crack density. In this study, NST was formed by reacting pre-patterned Ti thin films with H2O2 solution. Crack elimination was achieved when exposed Ti films were below a threshold dimension. Hydrated titanic gel crystallizes into anatase after annealing at 300°C for 8 hr. Crack elimination is thought to result from stress reduction in titanic gels due to patterning.; Oxidation of Ti films occurs by nucleation and growth mechanism. During growth, oxidation of Ti films with thickness 50 nm and below proceeds at a constant rate until films are fully consumed. For Ti films with thickness 100 nm or thicker oxidation rate reduces significantly after a period of growth. This reduction is attributed to a change in mechanism controlling growth of the hydrated titania gel layer.; Functionality of NST formed and compatibility of the process with current microelectronics manufacturing practices were demonstrated by exploring three applications. First, a prototype conductometric gas sensor was fabricated that used micrometer-scale NST pad arrays as sensing elements. This sensor is capable of detecting hydrogen and oxygen gas at concentration of a few parts per million (ppm). Second, micrometer scale Au-NST interpenetrating network nanocomposite contacts in micro-switches were fabricated by infiltrating NST features with Au using electroless deposition. Third, results of cell-culture studies showed that mouse fibroblast cells exhibited enhanced initial attachment on NST relative to silicon dioxide which is commonly used in microsystems devices for biological applications.