All-Semiconducting Nanotube Networks: Towards High Performance Printed Nanoelectronics
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All-Semiconducting Nanotube Networks: Towards High Performance Printed Nanoelectronics N. Rouhi, D. Jain, K. Zand, and P. J. Burke Electrical Engineering and Computer Science, University of California-Irvine, Irvine, CA 92697, U.S.A. [email protected]
ABSTRACT In this work, we present progress towards devices fabrication using all semiconducting nanotubes as the starting material. Individual nanotubes are known to have intrinsic mobility of more than 10,000 cm2/V-s but using a network of nanotubes will decrease this mobility because of tube-tube screening effect and junction resistance. Here we are using solution-based deposition of purified 99% semiconducting single-walled nanotubes as the channel in field effect transistors. DC analysis of devices’ characterization shows a high mobility, more than 50 cm2/Vs, and good on/off ratio in the range of more than 103 and 104. A critical issue is the ink formulation and dependence of electronic properties on the nanotube density after deposition. In addition, the channel length also plays an important role in controlling both mobility and on/off ratio.
INTRODUCTION So far different techniques have been utilized to fabricate carbon nanotube devices. To generally categorize these methods one can separate them in two major techniques, “depositing nanotubes” and “in-situ growth of nanotubes”. Depositing nanotube from a solution has been investigated recently to find the best way of having sorted network of semiconducting nanotubes 1-3. In addition to solution enrichment, semiconducting CNTs can be preferentially placed on wafers through modification of the wafer surface. It is now well known that amine terminated silanes such as 3-aminoprolyltriethoxysilane (APTES) when attached to the substrate surface, provide far better and selective deposition of semiconducting SWNTs (Single-Walled Nanotubes) 4. Such modifications increase the adsorption of nanotubes deposited from the solution and help the uniformity of the nanotube mat as well. For this study we combined both the processes, using semiconducting enriched solution of SWNTs and APTES assisted deposition of nanotubes. In this work, we present progress towards semiconducting nanotube field effect transistors using 99% semiconducting nanotubes as the starting material (this percentage is determined using spectroscopic methods such as Raman spectroscopy). Comparing to previous works 4-6 we are getting higher mobility while using more semiconducting enriched nanotubes in our devices. Moreover, we study the effect of various gate lengths, which reveals an interesting trend between the channel length and the mobility. High mobility and very good on/off ratio was achieved showing a great improvement in the device characteristics.
EXPERIMENT Devices reported here were fabricated using a solution enriched up to 99% in semiconducting single walled carbon nanotubes (diameter range – 1.2-1.7 nm, length range 300 nm to 5 µm). These solutions were made using density gradient centrifugation process for the separation of nanotubes with dif
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