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Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 159-164).

Point-of-care (POC) diagnostics presents a giant market opportunity with profound societal impact. In particular, specific detection of DNA and protein markers can be essential for early diagnosis of e.g. cancer, cardiovascular disease, infections or allergies. Today, identification of these markers often requires extensive laboratory work and hence is expensive and time consuming. Current methods for recognition and detection of specific biomolecules are mostly optics based and thus impose severe limitations as to convenience, specificity, sensitivity, parallel processing and cost reduction. Electronic sensors based on silicon nanowire field-effect transistors have been reported to be able to detect biomolecules with concentrations down to femtomolar (fM) level with high specificity. Although the reported capability needs further confirmation, the CMOS-compatible fabrication process of such sensors allows for low cost production and high density integration, which are favorable for POC applications. This thesis mainly focuses on the development of a multiplex detection platform based on silicon nanowire field-effect sensors integrated with a microfluidic system for liquid sample delivery. Extensive work was dedicated to developing a top-down fabrication process of the sensors as well as an effective passivation scheme. The operation mechanism and coupling efficiencies of different gate configurations were studied experimentally with the assistance of numerical simulation and equivalent circuits. Using pH sensing as a model system, large effort was devoted to identifying sources for false responses resulting from the instability of the inert-metal gate electrode. In addition, the drift mechanism of the sensor operating in electrolyte was addressed and a calibration model was proposed. Furthermore, protein detection experiments were performed using small-sized Affibody molecules as receptors on the gate insulator to tackle the Debye screening issue. Preliminary results showed that the directionality of the current changes in the sensors was in good agreement with the charge polarities of the proteins. Finally, a graphene-based capacitor was examined as an alternative to the nanowire device for field-effect ion sensing. Our initial attempts showed some attractive features of the capacitor sensor.

Hydrogenated amorphous silicon (a-Si:H) thin film transistors (TFTs) are used as switching elements in large area active matrix liquid crystal displays and various image sensing devices for radiation detection. The noise inherent in the a-Si:H TFTs contributes to the overall noise figure of such devices and degrades the signal to noise ratio; therefore, the noise is an important factor in the design of the devices. The noise of the a-Si:H TFTs has been studied experimentally, but the origin of the noise is not understood. <p> This work calculates the noise of the a-Si:H TFTs based on a simulation of operation of the TFTs and the hypothesis that the device noise is due to the intrinsic noise of the a-Si:H material. An a-Si:H TFT with an inverted-staggered structure has been simulated by numerically solving the fundamental transport equations for various gate and drain-source voltages. The drain-source curves derived from the simulation agree qualitatively with the experimental results: both the linear and saturated regions are observed. The low frequency noise was calculated based on the charge density distribution in the channel obtained from the simulation and the known dependence of the noise in the a-Si:H on the charge density, Hooges relation. The calculated noise power increases with the drain-source voltage and is inversely proportional to the gate voltage or the effective channel length. The curves agree qualitatively with the experimental results. The calculated noise power agrees quantitatively with the experiments when the scaling parameter in Hooges relation, , is set to . This value agrees with the experimentally determined value for a-Si:H. The results are consistent with the hypothesis that the low frequency noise in the a-Si:H TFTs is due to the material itself.

Graduation date: 1990

Hydrogenated amorphous silicon (a-Si:H) thin film transistors (TFTs) are used as switching elements in large area active matrix liquid crystal displays and various image sensing devices for radiation detection. The noise inherent in the a-Si:H TFTs contributes to the overall noise figure of such devices and degrades the signal to noise ratio; therefore, the noise is an important factor in the design of the devices. The noise of the a-Si:H TFTs has been studied experimentally, but the origin of the noise is not understood. <p> This work calculates the noise of the a-Si:H TFTs based on a simulation of operation of the TFTs and the hypothesis that the device noise is due to the intrinsic noise of the a-Si:H material. An a-Si:H TFT with an inverted-staggered structure has been simulated by numerically solving the fundamental transport equations for various gate and drain-source voltages. The drain-source curves derived from the simulation agree qualitatively with the experimental results: both the linear and saturated regions are observed. The low frequency noise was calculated based on the charge density distribution in the channel obtained from the simulation and the known dependence of the noise in the a-Si:H on the charge density, Hooges relation. The calculated noise power increases with the drain-source voltage and is inversely proportional to the gate voltage or the effective channel length. The curves agree qualitatively with the experimental results. The calculated noise power agrees quantitatively with the experiments when the scaling parameter in Hooges relation, , is set to . This value agrees with the experimentally determined value for a-Si:H. The results are consistent with the hypothesis that the low frequency noise in the a-Si:H TFTs is due to the material itself.

Thesis (Ph. D.)--University of Texas at Austin, 2001. / Vita. Includes bibliographical references. Available also from UMI/Dissertation Abstracts International.

Thesis (Ph.D.)--Tennessee Technological University, 2009. / Title from title page screen (viewed on Feb. 10, 2010). Bibliography: leaves 146-153.

Thesis (Ph. D.)--University of Texas at Austin, 2002. / Vita. Includes bibliographical references. Available also from UMI Company.

Thesis--Ph. D., University of Hong Kong, 1985.