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Exploring Properties of Suspended ZnO Nanowire FET

This study delves into the characteristics of suspended ZnO nanowire field-effect transistors, focusing on gas and chemical sensing applications, optoelectronics, micro-lasers, and NW synthesis. Techniques for improving electrical contacts and experimental sensor results are discussed, with future objectives outlined. The advantages and objectives of ZnO nanowires are explored, along with synthesis methods and fabrication processes. The study also touches upon nanowire properties under scanning probe microscopy, highlighting electrical properties and surface potential results.

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Exploring Properties of Suspended ZnO Nanowire FET

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  1. Properties of Suspended ZnO Nanowire Field-Effect Transistor Scott Cromar Mentor: Jia Grace Lu University of California, Irvine 31 August 2006

  2. Wide & direct bandgap semiconductor (Eg=3.35 eV) Field effect transistors (FETs) Gas & chemical sensing Optoelectronics & Micro-lasers NW Synthesis Suspended ZnO NW FET fabrication Electrical contact improvement techniques Sensing experiment results Next step ZnO Nanowires (NWs) Advantages Objectives Fan, Z.; Lu, J.G. "Zinc Oxide Nanostructures: Synthesis and Properties." Journal of Nanoscience and Nanotechnology 5 (2005): 1561-1573.

  3. Nanowire Synthesis O2 O2 Catalyst Zn Au catalyst ZnO nanowire Vapor Trapping Chemical Vapor Deposition (CVD) • Absorbs Zn • Vapor • Au-Zn Alloy • Supersaturation • Nucleation • 1D Crystal Structure • ZnO Nanowire • Au Catalyst • 700 °C Chang, P.-C.; Fan, Z.; Wang, D.; Tseng, W.-T.; Chiou, W. -A.; Hong, J.; Lu, J. G. “ZnO nanowires synthesized by vapor trapping CVD method.” Chem. Mater. 16 (2004): 5133-5137

  4. Nanowire Synthesis Furnace Diameter = 30-100 nm O2 Gas Flow Zn Vapor Zn Powder Quartz Vial Quartz Tube Si Chip

  5. Nanowire Synthesis

  6. Sonicate NW chip in isopropanol Drop solution on pattern, Ti/Au contact Search for device w/ optical microscope ZnO NW FET Fabrication

  7. ZnO NW FET Fabrication Nanowire (Channel) Source Drain Gate Ti/Au SiO2 Vds P++Si Vg

  8. ZnO NW FET Fabrication

  9. Annealing 300 - 700 °C, 30 min. Metal deposition w/ Focused Ion Beam Improve Contact

  10. Gas Sensing Depletion Region NW Channel Source Drain Gate • NWs have high surface-volume ratio • Suspended NW have more surface area than nonsuspended • Gas molecules on metal-oxide surface alter the electronic properties by chemisorption Fan, Z.; Lu, J. G. “Chemical sensing with ZnO nanowire field-effect transistor.” IEEE Transactions on Nanotechnology 5 (2006): 393-396.

  11. Gas Sensing Results • Sensitivity: • Nonsuspended: 90% • Suspended: 10% I-Vds curve for various concentrations of NO2 Conductance of NW exposed to 1000 ppm CO2 Ggas= Transconductance on gas exposure G0 = Trasconductance in inert environment

  12. Next Step • Further investigate the intrinsic properties of suspended ZnO NWs • More gas sensing • Gating characteristics • Mechanical & electrical properties w/ SPM • Identify device applications

  13. Acknowledgements • Professor Jia Grace Lu • CJ Chien • Joseph Fan • IM-SURE staff • Carl Zeiss Inc. (SEM use) • Funding through NSF

  14. Scanning Probe Microscopy (SPM) Scanning Surface Potential Microscopy (SSPM) Surface Potential Results F = electrostatic force dC/dz = derivative of the tip-sample capacitance Vac = magnitude signal applied tip Vtip – Vsample = potential difference between tip and sample Fan, Z.; Lu, J. G. “Electrical properties of ZnO nanowire field effect transistors characterized with scanning probes.” Applied Physics Letters 86 (2005): 032111.

  15. Surface Potential Results Surface Topology Surface Potential

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