Fabrication and characterization of radio-frequency sensors for liquid material detection

This thesis presents a series of studies on fabrication and characterization of radio-frequency (RF) sensors. In the light of Electromagnetics and Transmission Line Theory, we designed multiple RF sensors with different detection capability emphasis and used them to detect various materials, especially liquid samples and materials in solutions such as dielectric thin films, confined liquids, red blood cells, and malarial pigments (hemozoin). Most sensors were fabricated under clean room environment following the standard process protocols. Proper process developments were also made to achieve special structures and functionalities of our novel sensors. Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) were used to inspect and control fabrication quality. The main characterization techniques we applied include on-chip interference process, RF signal cancellation, micro/nanofluidics, single cell manipulation, and electron paramagnetic resonance (EPR). Through the whole process, sensors and measurement systems have been adjusted constantly and the characterization capabilities have been optimized. Our measurements and analysis have proved that RF sensors based on transmission lines could be very powerful detection tools comparing with other approaches currently in use for chemical and biomedical materials on both bulk and molecular levels. The main strength of RF sensors resides in the fact that they are able to work cost-efficiently, non-invasively and fast without involving powerful microscopy tools. Meanwhile, they promise to provide large amount of information with high sensitivity and resolution. Further work is needed to enhance the sensors' capabilities quantitatively and expand the usage to additional applications.