1,309 research outputs found
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Two-Dimensional, Individually-Addressable Nanostructure Arrays
Full text linkAbstractTwo-Dimensional, Individually-Addressable Nanostructure ArraysbyChu-Yeu Peter YangDoctor of Philosophy in Mechanical EngineeringUniversity of California, BerkeleyProfessor Liwei Lin, Chair Assembly and integration of vertically-oriented, one-dimensional nanostructures into a two-dimensional array platform has been demonstrated. This 2D architecture is realized using top-down semiconductor and microelectro-mechanical system (MEMS) processes as well as bottom-up catalyst-assisted 1D nanostructure synthesis methods. Two prototype demonstrations include: (1) a 15×12 carbon nanotube (CNT) array and (2) a 2×5 ZnO nanowire array systems. Arrays based on CNT structures have been developed to verify the feasibility of the 2D architecture using vertically-oriented nanostructures. A trench process is conducted by dry etching into a silicon substrate. A CNT growth process follows to fill the trenches while top electrodes are defined by metallization with a shadow mask. Measurement results show that the average resistance value from the 15×12 CNT electrodes with a contact area of 500×400 um^2 was several tens of ohms. To get a better understanding for the electrical characteristics of the as-fabricated CNT structures, a single 1 um-long CNT sample with measured diameter of 30 nm was attached to two nanoprobes inside a scanning electron microscope. Its resistivity was characterized as 0.056 ohm-m and the overall resistance value of the CNT nodes in the 2D array was estimated at 41 ohms;. This result correlates well with measured resistance values from the CNT nodes, suggesting that there are successful electrical connections between the top and bottom electrodes through the CNT bundles. Individual-addressability of the 2D architecture has been enabled by replacing the metallic CNTs with semiconducting ZnO nanowires and creating rectifying, Schottky diodes at the array nodes. A 2×5 array featuring asymmetric bottom platinum-nZnO Schottky junctions and top nZnO-titanium/gold ohmic contacts was fabricated. ZnO nanowires were first synthesized atop of metal electrodes on a silicon substrate. After applying spin-on-glass, the tips of the nanowires were exposed by plasma etching and top metal electrodes were deposited. The I-V characteristics of a 150×500 um^2 node under forward and reverse biases with and without a 40 um-wide UV laser beam were tested. It is found that a photogenerated current is detectable from the 2D array with an estimated responsivity of 3×10^-4 A/W. Moving the laser beam to neighboring nodes did not result in an increased current from the interrogated node, demonstrating the individual-addressability of the 2D ZnO nanowire array and its capability for discrete pattern recognition as a UV photodetector. This marks the first successful demonstration of vertically integrating ZnO nanowires into an individually-addressable 2D array for possible ultrahigh-density applications in nanoelectronic memory, information displays, photodetectors, and nano-lithography
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Metal Oxides for Solid State Electronics: Transparent Electrodes, Photoanodes and Transistors
Full text linkAbstractMetal Oxide for Solid State Electronics: Transparent Electrodes, Photoanodes and TransistorsbyHyun Sung ParkDoctor of Philosophy in Engineering - Mechanical Engineering University of California, BerkeleyProfessor Liwei Lin, ChairMetal oxides have unique characteristics for a variety of modern applications such as thin films and nano-structured materials in optoelectronic devices and renewable energy productions. In this dissertation, three different metal oxides are developed: solution processed antimony doped tin oxide (ATO) thin films for transparent electrodes; high aspect-ratio ZnO nanowires with ALD (Atomic Layer Deposition) TiO2 for stabilizations as photo-anodes; and spin-coated SnO2 films for TFTs (Thin Film Transistors) in the applications of display devices.In the first part of this dissertation, solution processed ATO electrodes show high conductivity (~21000 S/m) and optical transparency (~95%) suitable for the state-of-art optoelectronic devices such as displays, solar cells, and smart windows. The high quality thin films are made by the low-cost solution-based process with multiple spin-coating steps using sol-gel precursors. In order to obtain better electrical and optical performances, a parametric study has been performed on four key processing parameters: doping concentration, film thickness, ambient gases and temperatures. Studies on the film surface morphology using scanning electron microscopy together with electrical, and optical characterizations elucidate the dominant factors for the conductivity and transmittance of the films. Further examinations under X-ray photoelectron spectroscopy reveal the required annealing temperature to form Sb+5 species in the Sn+4 lattices. It is found that improved mechanical flexibility is achieved and the elastic modulus of 35GPa is obtained by using the nano-indentation test. A 3D finite element analysis shows ATO films can resist 4x more deformation than those of commercial vacuum-processed indium tin oxide (ITO) films under the four-point bending simulations.The high aspect-ratio and vertically ordered ZnO nanowires as long as 10μm in length and 50nm in the cross-sectional width are constructed by using a hydrothermal process. A conformal TiO2 film of 40nm in thickness is deposited afterwards by ALD to stabilize the ZnO nanowires in a solar-powered hydrogen gas harvester. Two key innovations have been achieved using the favorable geometry and high quality nanowires in this work: (1) improved stability over bare ZnO nanowires during the photocatalytic reactions, and (2) excellent low bias voltages.In the work of using SnO2 films to make TFTs for display devices, a multiple spin coating is developed in order to obtain better gate modulation properties. The effects of annealing condition on the electrical performances and the surface morphologies of TFTs have been investigated. Experimentally, a value of 6.3cm2/Vs of the extracted field effect mobility for solution processed SnO2 TFTs has been achieved and this value is 6x higher than that of a-Si:H TFTs
A closed-form approach for frequency tunable comb resonators with curved finger contour
No full textFrequency tunable comb resonators have been successfully designed and demonstrated based on a closed-form approach of a curved comb finger contour. Experimentally, the resonant frequency of a laterally driven comb resonator with 186 pairs of curved finger contour has been reduced by 55% from the initial frequency of 19 kHz under a bias voltage of 150 V The corresponding effective stiffness has been decreased by 80% from the initial value of 2.64 N/m. This closed-form design approach could be extended to microsystems based on electrostatic comb-shape structures such as microaccelerometers, microgyroscopes, and micromechanical filters. (c) 2007 Elsevier B.V. All rights reserved
Surface micromachined diaphragm pressure sensors with optimized piezoresistive sensing resistors
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