CNT as a Sensor Platform

CNT as a Sensor Platform

Amir Fathi (Urmia University, Iran) and Mina Hassanzadazar (Urmia University, Iran)
DOI: 10.4018/978-1-5225-0736-9.ch001
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Abstract

One of the most important drawbacks which caused the Silicon based technologies to their technical limitations is the instability of their products at nano-level. On the other side, carbon based materials such as carbon nanotube (CNT) as alternative materials have been involved in scientific efforts. Some of the important advantages of CNTs over silicon components are high mechanical strength, high sensing capability and large surface-to-volume ratio. Many researches have been presented using CNT as a sensing material in various applications to improve the sensor characteristics. In this chapter, the platform of CNT sensors such as transistor-based sensors, chemiresistors, chemicapacitance and resonator sensors are discussed in detail. Using CNT as a sensor platform although has great advantages; it does not have sufficient sensor reliability. Some of these technical challenges of CNT-based sensors including Schottky contact formation and non-selective synthesization have also been pointed out in the chapter.
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Introduction

Carbon nanotubes (CNTs) can be assumed as a single layer graphene rolled up in the cylindrical form as illustrated in Figure 1 (Dresselhaus, Dresselhaus, & Eklund, 1996). CNTs, especially single-walled carbon nanotubes (SWCNTs), are considered undertaking materials for next generation of electronic applications.

Figure 1.

Carbon nanotubes structure as a rolled up graphene

The strength and flexibility of CNTs are the key factors which make them eligible to control other nanoscale compounds. These factors suggest they will have an important role in nanotechnology engineering. During the recent years, they have drawn the attention of IC designers because of their unique electrical properties (Lu & Chen, 2005). Owing to their specific configuration and their special electronic properties (Lu, 2005; Wei, 2001; Treacy, 1996; Zhang, 2004; Hone, 2000), CNTs have been highly considered for the development of new generation of gas and biosensors. Different sensing approaches have been reported to increase the speed and accuracy of sensors using CNTs.

The most currently-used structure among all sensor platforms is transistor-based sensors using CNTs as conducting channels (Martel, 1998; Kong, 2000; Someya, 2003; Collins, 2000). Although CNT-based nanosensors have great advantages but they meet many limitations, such as sometimes low sensitivity, long recovery time and low selectivity (Modi, Koratkar, Lass, Wei & Ajayan, 2003). Several techniques are reported to overcome these limitations to provide fast, stable and analyte-specific sensors. However, the methods still fail to suggest a commercial successful CNT-based sensor design for various applications. In this chapter, the CNT sensors platform, the design hurdles, advantages and some applications of the sensors are demonstrated in detail.

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Background

A misunderstanding in the origination of CNTs is caused by an editorial written by Monthioux and Kuznetsov (2006). But several unrivaled CNT properties have been found and reported from the standpoint of electrical and elastic modulus, respectively. In the near future, they are expected to play a dominant role in the designation of many nano-material based devices (Yu et al., 2000). A large percentage of research literature ascribes graphitic carbon as the origin of hollow, nanometer-size tubes (Yu et al., 2000). Until 1991, many efforts are done to produce and perceive CNTs under different conditions in order to study their properties. In a research published by Oberlin, Endo, and Koyama (1976) and by means of a vapor-growth technique, hollow carbon fibers with their nanometer-scale diameters are exhibited vividly. Additionally, a single wall of graphene is demonstrated by the authors in a transmission electro microscopic (TEM) image of a nanotube. Later, this image has been attributed as a single-walled nanotube by Endo (Endo & Dresselhaus, 2002).

Nowadays, many primary devices are being fabricated using CNTs, including field-effect transistors (FETs), diodes, single electron transistors, nanoelectrodes, and several others (Postma Henk, 2001; Collins, 2001; Wong, 2002). Their main advantage was 20–30x higher ON current in comparison with Si MOSFETs. This was an important advantage in this field as CNT was displayed to potentially perform better than Si (Javey, Guo, Wang, Lundstrom & Dai, 2003) and it is because of their higher carrier velocity along with ballistic transport (Geetha, 2014; Sharifi, 2015).

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