Electrical performance of carbon nanotube-polymer composites at frequencies up to 220 GHz

Abstract

We have measured the sub-THz electrical response of screen printed carbon nanotube -poly(methyl methacrylate) polymer composites up to 220 GHz. The measured electrical losses using mm long coplanar waveguide geometries averaged as low as 0.15 dB/mm in the frequency range 40 GHz to 110GHz and showed a reduction in signal loss with increasing frequency; a behaviour opposite to that found in conventional metallic conductors. Between 140 and 220 GHz the electrical losses averaged 0.28 dB/mm. We show that the low electrical losses are associated with the capacitive coupling between the nanotubes and discuss potential high frequency applications. *Corresponding authors: A.Alshehri@surrey.ac.uk (Ali Alshehri) and David.Carey@surrey.ac.uk (J David Carey) 2 Carbon nanotube (CNT) electronics has firmly established itself as one of the most important areas of modern nanoelectronics. 1, 2 The suppression of carrier backscattering brought about by the nanotube's band structure results in long mean free paths leading to ballistic transport and opens up the possibility of GHz and sub-THz applications. 3 Tailoring the intrinsic electronic properties of the CNT by choosing semiconducting or metallic CNTs has already led to the fabrication of field effect transistors 3 and sensors 4 for the former type of nanotube and interconnects 5 and field emission materials 6 for the latter.Previous high frequency studies of CNTs have tended to concentrate on employing small (micron) electrode gaps, often making use of single or few singlewalled nanotube bundles as the active elements in a transistor architecture. 3 Chemical vapor deposited (CVD) carbon nanotubes bundles 7 , vertically aligned arrays 8 or nanotube ropes 9 for possible applications as electrical interconnects have also been variously explored. However such measurements using short CNTs bundles are often affected by the presence of parasitic capacitances associated with the electrodes and the presence of large impedance mismatches.Electrode architectures for transistors and interconnect applications imposes strict requirements for the environment that the nanotube can be found. Using a CNT composite frees up many of these constraints and at high frequency opens up the possibility of using large area, high bandwidth CNT electronics for communications, microwave and surface acoustic wave devices. In this Letter we have successfully characterised up to 25 mm long CNT -poly(methyl methacrylate) polymer composites up to 220 GHz. We show that the frequency response of the composites is significantly different from that of conventional metallic conductors and that capacitive coupling between the nanotubes plays an important role in the ac conduction.The samples characterised consisted of CVD grown multiwalled CNTs (average length 1.5 m, average diameter 9.5 nm, Nanocyl batch number NC3100) mixed with poly(methyl-methacrylate) (PMMA) to produce composites with 10 wt.% CNT loading. Apart from its ready availability and compatibility with high frequency electronics, PMMA was chose...

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