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Patterning of Carbon Nanotubes by Material Assisted Laser Ablation Process


Abstract:

Carbon nanotubes were patterned by a nonphotolithographic, low energy, large area, and high-throughput laser patterning process [material-assisted laser ablation (MALA)]....Show More

Abstract:

Carbon nanotubes were patterned by a nonphotolithographic, low energy, large area, and high-throughput laser patterning process [material-assisted laser ablation (MALA)]. In this process, a residue layer was observed after the patterning process, requiring an additional cleaning process for the fabrication of electronic devices. In this paper, we investigated the mechanism of the residue layer formation, and optimized the MALA process so that no residue layer is formed after the patterning of carbon nanotubes. We demonstrated patterning of carbon nanotubes on 100 mm diameter silicon wafers, and the patterns of carbon nanotubes were sufficiently clean and sharp to be applicable in high-volume fabrication of electronic devices.
Published in: IEEE Transactions on Nanotechnology ( Volume: 9, Issue: 3, May 2010)
Page(s): 381 - 385
Date of Publication: 25 August 2009

ISSN Information:


I. Introduction

Carbon nanotubes have attracted a great deal of interest due to their potential for sensors [1], biomedical applications [2] and [3], displays [4], and electrical applications [5]–[8]. In the fabrication of carbon nanotube devices and applications, patterning of carbon nanotubes is one of the essential steps in the whole fabrication processes. There has been much research on patterning methods for carbon nanotubes, and one of these methods uses the prepatterning of a catalyst material. In this method, a ferrite catalyst is first patterned on the substrate and then carbon nanotubes are grown selectively on the prepatterned catalyst [9], [10]. However, this method is of limited value because ferrite catalysts are not compatible with complementary metal oxide semiconductor (CMOS) materials. Additionally, growing carbon nanotubes on the catalyst needs high process temperatures, commonly 600 °C or higher. Therefore, it is not possible to use this method for carbon nanotube patterning on flexible electronics, which is expected to be one of the main applications of carbon nanotubes in the future. Chemical anchoring [11] and electrophoresis [12] have also been investigated but they are not suitable for high-volume production of carbon nanotube devices. A process for fabricating fine feature patterns of carbon nanotubes by using conventional photolithography and high-density oxygen plasma etching has been reported to be CMOS compatible [13], [14]. However, a high-density plasma process is not suitable for large-area substrates because achieving uniform density of the plasma is difficult on large areas, and handling of flexible substrates is challenging in a vacuum system. Also, patterning by conventional photolithography and etching involves many process steps; thus, the method requires significant equipment and resources [15]. Besides the complexity of the conventional patterning method, there are several requirements on the patterning process for carbon nanotubes if it is to be used in a high-volume application. First of all, the patterning process should be compatible with CMOS processes in order to utilize current manufacturing technologies. Second, the patterning process should have high throughput and high yield in high-volume production applications. Direct ablation of carbon nanotubes can be another method of patterning the carbon nanotubes, but this method requires very high energy due to strong and stable bond structure of carbon nanotubes [16]. Substrates as well as devices that are fabricated on the substrate could be damaged by high-energy laser radiation, if direct ablation is used. Therefore, direct patterning of carbon nanotubes by direct laser ablation is not practical for fabrication of electrical components by conventional microelectronic fabrication processes. Recently, we reported a new patterning method called material assisted laser ablation (MALA) for patterning of carbon nanotubes and other nanowires that meets all of the requirements of high-volume production applications [16], [17].

References

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