NER: Carbon Nanotube Devices and Integrated Systems

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PROPOSAL NO.: 0102955PRINCIPAL INVESTIGATOR: Zhou, ChongwuINSTITUTION NAME: University of Southern CaliforniaTITLE: NER: Carbon Nanotube Devices and Integrated SystemsThis is a proposal to design, build and evaluate various novel nanotube devices andintegrated systems. Specifically I propose to make n type field effect transistors (FET),nanotube p-n junctions, and an integrated single-molecule CMOS inverter. This researchis exploratory in nature; however, if successful, will advance our understanding of thefundamental properties of nanotubes and produce practical nanoscale devices for the realworld.There has been a great deal of research into carbon nanotubes in the past few years. Ptype field effect transistors have been demonstrated consisting of semiconductivenanotubes with a silicon substrate backgate separated from the tube by a layer of SiO2.Despite the utmost interest in developing n type FETs to enable nanoscale CMOScircuits, the research effort has been hampered by lack of an effective doping method fornanotubes. I propose to demonstrate a simple, effective and reliable method toelectrostatically dope nanotubes into n type, thus paving the way for n type FETs, p-njunctions and integrated systems. This new method will employ TiO2 instead of SiO2 asthe gate dielectric. With a dielectric constant of 30 for TiO2, as compared to 3.8 for SiO2,the gate utilizing TiO2 will be seven times more effective than previously reported, andour preliminary analysis confirms that with a reasonable gate bias (~ 10 V), a nanotubecan be electrostatically doped into n type, thereby producing an n type FETs.Furthermore, carbon nanotube p-n junctions will be demonstrated with a split-gatetechnique, by depositing TiO2 onto a semiconductive nanotube contacted with source anddrain electrodes, and patterning two gate electrodes atop the TiO2, each covering half ofthe tube. By controlling these two gate biases independently, one can tune the left halftube into p type and the right half into n type, thus creating a p-n junction in between,which provides an ideal system for studying the depletion and screening in onedimension.Finally, a simple integrated system will be demonstrated by attaching an electrode to thecenter of a semiconductive nanotube in addition to the source and drain electrodes. Thiscenter electrode divides the nanotube into two segments and serves as the output of thecircuit. The silicon substrate backgate with TiO2 dielectric layer will serve as the circuitinput and be used to tune one tube segment to function as an n type FET and the othersegment as a p type FET, thereby forming the worlds first single molecule inverter.