Most Popular Books by Jen Wang

Optically transparent, wide bandgap metal oxide semiconductors are a promising candidate for large-area electronics technologies that require lightweight, temperature-sensitive flexible substrates. Because these thin films retain relatively high carrier mobilities even in an amorphous state, metal oxide-based field effect transistors (FETs) can be processed at near-room temperatures. Compared to amorphous silicon FETs, which are the dominant technology used in display backplanes, metal oxide FETs have been demonstrated with higher charge carrier mobilities, higher current densities, and faster response performance. In this thesis we present a low-temperature ('1000C), scalable, fully lithographic process for top-gate, bottom-contact amorphous zinc indium oxide FETs using parylene, a room-temperature-deposited CVD polymer, as gate dielectric. Electrical characteristics were compared for FETs of varying device dimensions (W, L) using a standard set of extracted device parameters. We show in both simulation and experiment that the FET threshold voltage can be modified by varying the channel thickness alone, without requiring the additional complexity of multiple channel materials or different dopings. The baseline lithographic process was further developed to enable the integration of FETs of different channel thicknesses, and hence threshold voltages, on a single substrate. The availability of FETs with different threshold voltages allows the implementation of enhancement-depletion (E/D) logic circuits that have faster speeds and smaller device areas than single-VT topologies. Using the two-VT lithographic process, we fabricated integrated E/D inverters that operate at VDD as low as 3V with gains > 20 and symmetric noise margins ~1.2V. Furthermore, we demonstrated integrated 11-stage and 21-stage E/D ring oscillators that operated rail-to-rail at VDD= 3V and maintained oscillation for VDD as low as 1.7V. These results demonstrate the potential for low VDD metal oxide-based integrated circuits fabricated in a low temperature budget, fully lithographic process for large-area transparent electronics.

Improvement of manufacturing productivity is dependent on the successful automation of manufacturing processes, the success of which is based in turn upon the availability of information which describes the state of manufacturing operations. Acoustic Emission (AE) signals related to the cutting process and tool wear have been recently applied to monitor manufacturing processes, and various AE parameters can be used to provide process information. For example, when cutting tools become worn, AE energy generated at the interface of tool flank and work piece increases. This study is thus an experimental investigation of the AE spectrums representing AE signals energy distribution to determine the possibility of extracting useful parameters to provide on-line information about drilled-hole quality and drill-bit wear. An experiment conducted using a radial-arm drilling machine was employed to collect on-line AE drilling process spectrums, yielding eight indicator parameters. Drill wear states were measured using a machine vision system. Assessment of the drilled hole quality was based on tolerances established in Geometric Dimensioning and Tolerancing (GD & T). Correlations among drill wear, drilled-hole quality measurements, and the AE spectrum indicator parameters were examined by regression analysis. A forward-stepwise variable selection procedure was used to select the best-fit regression model for each drilled hole quality measurement associated with the set of one AE parameter raised to different powers. According to quality measurements, drilled holes were categorized as either "acceptable" or "unacceptable" holes, using cluster analysis with a group-averaging method. The usage of AE parameters to decide to which group a drilled hole belonged was also examined. From the experimental evidence, it was observed that there are strong relationships between AE parameters and drill-wear state and the quality measurements of drilled holes. AE parameters could be useful predictor variables to provide information to controller/operators to evaluate current drilling processes. Based on the status information of drill wear and the quality measurements, drilling processes can be adjusted accordingly.