| The research work presented in this thesis focuses on three topics: (1) studies of several critical aspects of nanoimprint lithography (NIL), including methods of mold pressing, air bubble defects, and dynamic behaviors of liquid resist flow; (2) applications of NIL to the fabrication of novel nanofluidic devices, which can be used for real-time DNA detection; and (3) additional applications of structured stamps or templates in the direct engineering of functional materials. Based upon these topics, the thesis is divided into three parts.; The first part describes recent studies of critical techniques of NIL. First, a novel imprint approach using electrostatic force was developed to pattern spin-on resists in ambient environment. Using this Electrostatic Force-Assisted NIL (EFAN) approach, highly uniform imprints over a 4" diameter wafer area and sub-0.5 mum overlay precision were obtained using very simple equipment. Second, another important method for performing step-and-repeat imprint in the atmosphere, dispensing-based NIL, still suffers from air bubble defects formed by feature pinning and the circling of residual air by the merge of multiple resist droplets. However, it was found that the tiny bubbles can be completely absorbed by the liquid resist. The effects of several key parameters, such as bubble size, imprinting pressure, resist viscosity and solubility, and residual layer thickness, on the air dissolution rate were studied experimentally and theoretically. Their impact to the yield and throughput of NIL was also analyzed. Third, a novel method was developed for filling liquid resists into the air gap between the structured mold and the substrate. The method is assisted by dielectrophoresis, caused by electrohydrodynamic force.; The second part describes the applications of NIL to making nanofluidic channel devices and device integration. First, a novel imprint-based method was developed to fabricate precisely positioned single nanofluidic channels of uniform channel width (11 to 50 nm) and over-1.5-centimeter-length. These are essential to developing innovative bio/chemical sensors (e.g. a real-time DNA analyzer). The continuity through the whole channel length was verified by flowing fluorescent dye-contained water, stretching and transporting DNA strands, and measuring ionic current. Afterwards, additional device units were integrated inside a single nanofluidic channel to fabricate a novel real-time, label-free DNA detector. In this DNA detector, a long nanofluidic channel stretches a DNA strand, and a nanogap detector (with a gap as small as 9 nm) inside the channel measures the electrical conduction perpendicular to the DNA backbone as it moves through the gap. Electrical signals were observed and associated with 1.1 kilobase-pair (kbp) double-stranded (ds) DNA molecules passing through a sub-13 nm gap in the nanogap detectors.; The third part addresses an additional application of structured templates or stamps in engineering the functional material - graphenes. We use structured stamps to cut and exfoliate graphene islands from a graphite substrate, and then transfer-print the islands from the stamp into the device active-areas on a substrate. The placement accuracy is potentially nanometers. The process can be repeated to cover all device active-areas over an entire wafer. Transistors fabricated from the printed graphenes exhibit excellent performance. |
