Nano-resonators for high resolution mass detection

Zachary James Davis

    Research output: Book/ReportPh.D. thesis

    184 Downloads (Pure)

    Abstract

    Cantilever based sensors have been demonstrated to be a very flexible and wide ranging micro-electro mechanical system (MEMS). Compared to static mode, dynamic mode operation of cantilever based systems are able to measure both stress and pure mass changes of the cantilever. Furthermore, by reducing the dimensions of the sensor to the nanometer scale, the sensor can become faster, cheaper and more sensitive.

    The goal of this Ph.D. project has been to design, fabricate and characterize a cantilever based mass sensor. The design of the device is based on electrostatic actuation of a laterally vibrating cantilever and the readout is based on measuring capacitance changes between the vibrating cantilever and a static parallel electrode. Furthermore, the width of the cantilever is to be reduced to the submicrometer scale in order to increase the mass sensitivity and spatial resolution.

    In order to facilitate with the design a model of the capacitive based device has been developed. This model is based on SPICE and is able to simulate both the mechanical and electrical behavior of the device. It was found through simulations that the capacitive readout of the device is only possible if the parasitic capacitances are very low, due to the sub-micron dimensions of the cantilever device. This lead to the integration of the mass sensor with CMOS technology. By integrating the mechanical device with CMOS circuitry, the parasitic capacitances are reduced enough to achieve capacitive readout. Furthermore, the CMOS can be used to increase the functionality of the sensor.

    It was decided that, as a first attempt, the fabrication of the cantilever will be a post processing module using one of the CMOS poly-Si layers. A post processing
    sequence for fabricating 500nm wide laterally vibrating cantilevers on CMOS circuitry was developed. Furthermore, fabrication of cantilevers that have been defined by laser and E-beam lithography has been successful. In addition, singlecrystal Si and Al, non-integrated cantilevers, have been fabricated using atomic force microscopy (AFM) and UV lithography respectively.

    Non-electrical characterization has been performed on poly-Si test cantilever in and out of vacuum in order to determine the sensor performance. Furthermore, electrical characterization of a CMOS integrated cantilever has also been performed.

    Mass measurements have been performed using vertically vibrating Al cantilevers. The measurements have been performed in vacuum using the SEM detector signal as a readout for the cantilever. Electron beam induced deposition (EBID) was used to deposit carbon on the apex of the cantilever.
    Original languageEnglish
    Place of PublicationKgs. Lyngby, Denmark
    PublisherTechnical University of Denmark
    Number of pages150
    ISBN (Print)87-89935-58-6
    Publication statusPublished - Jun 2003

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