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David Estrada Master's ThesisPDF


Title:Electrical and thermal characterization techniques for carbon nanotube transistors and networks
Author(s):Estrada, David
Advisor(s):Pop, Eric
Department / Program:Electrical and Computer Engineering
Discipline:Electrical and Computer Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Carbon Nanotube (CNT)
Electrical Thermometry
Abstract:In this study, pulsed measurement techniques to suppress hysteresis in carbon nanotube (CNT) field-effect transistor (CNTFET) transfer characteristics are demonstrated. As hysteresis is reduced, both forward and backward gate voltage sweeps move toward a common, unique central transfer characteristic that reveals the “true” device mobility. Time constants associated with environmental charge trapping, at various ambient temperatures from 80 to 453 K are extracted. Hysteresis dependence of pulsed measurements is compared under air, high-temperature, and vacuum conditions. Using such measurements we investigate the error on carrier mobility associated with mobility extractions from forward and backward DC gate voltage sweeps. A pulsed electrical breakdown technique to increase the ION/IOFF ratio of carbon nanotube random network transistors is also demonstrated. The ratio is increased by three orders of magnitude, with minimal reduction in ION (< 50%). It is shown that adsorbed water rather than oxygen promotes nanotube breakdown. Finally, the design of an electrical thermometry platform for measuring the thermal properties of nanoscale films is presented, with possible application to single-walled CNT random networks and perfectly aligned arrays. The platform is freely suspended to confine heat flow to one dimension, leading to challenging stress patterns in the constituent SiO2 membrane. Using sputtered SiO2 reduces stress by a factor of 20 and results in a “flatter,” more robust membrane for thermal measurements. Methods of incorporating CNT networks in the device fabrication process are discussed. As a calibration step, the thermal conductivity for a 320 nm freestanding thin film of RF sputtered SiO2 is found to be 0.45 Wm^-1K^-1 at 300 K, in agreement with previous measurements of thin SiO2 films on bulk Si.
Issue Date:2009
Genre:Dissertation / Thesis
Publication Status:unpublished
Date Available in IDEALS:2010-11-23

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