ABSTRACT

C60 fullerene nanowhiskers (FNWs) have been investigated for electronics device applications. Nanofabrication for C60 FNWs has been developed for device manufacturing based on simple synthesis and semiconductor microprocessing of C60. Several kinds of disadvantages, including carrier suppression, were overcome under the control of the device structure. Electrical transport is explained and the device working characteristics of the field-effect transistor are also discussed. Fullerene Nanowhiskers Edited by Kun’ichi Miyazawa Copyright © 2012 Pan Stanford Publishing Pte. Ltd. www.panstanford.com

15.1 INTRODUCTIONThere is much interest in nanostructured carbon materials for electronics device applications, since organic thin-film field-effect transistors (FETs) have been widely investigated from the perspective of developing near-future device applications.1 Especially, the practical performance of C60 fullerene and carbon nanotubes should be tested in standard device components, such as FETs, as tentative device elements in practical circuits. The important criteria for the performance of such FETs are commonly considered to be a field-effect electron mobility of 1 cm2/(V s) or more and an on/off ratio of the order of 106. In the case of the well-known organic semiconductor, a penthacene mobility of 1.5 cm2/(V s) was achieved using one monolayer based on a SiO2 surface treatment technique. However, such FETs show only p-type character in their operation. In C60 fullerenes, the thin film FET performance is n-type in character but the mobility is relatively low, while a higher mobility has been reported recently.2 Therefore, improved performance of n-type C60 FETs is highly desired. An additional difficulty for this system is that the n-type behavior of C60 FETs is very sensitive to oxygen or ambient atmosphere, since the conductance quickly decreases by several orders due to oxygen adsorption in air. Consequently, usual device operation is achieved only for C60 FETs under vacuum. It is considered that the absorbed oxygen generates deep trap centers and suppresses carrier transport in C60 thin films. By covering the FET with a protective layer, such as a thin insulating layer of alumina, one can prevent carrier suppression in C60 thin films.3 Especially, the alumina covering can also be used for a gate insulator with a large dielectric constant in order to obtain good electric breakdown properties; however, special handling and processing of alumina is needed.Also there exist a few problems that arise in the practical application of C60 fullerenes and involve the use of nanofabrication processes based on electron-beam (E-B) lithography. On exposure of an E-B on C60, its surface gets damaged and its resistance largely increases. Several preparation processes performed before and after E-B lithography clearly affect the electrical quality of C60 layers.