Abstract
The electrical impedance characteristics of multi-walled carbon nanotube (MWCNTs) networks were studied as a function of CNT concentrations in the frequency range of 1 kHz–1 MHz. The novelty of this study is that the MWCNTs were not embedded in any polymer matrix and so the response of the device to electrical measurements are attributed to the CNTs in the network without any contribution from a polymer host matrix. Devices with low MWCNT packing density (0.31–0.85 µg/cm2) exhibit a frequency independent plateau in the low-frequency regime. At higher frequencies, the AC conductivity of these devices increases following a power law, characteristic of the universal dynamic response (UDR) phenomenon. On the other hand, devices with high MWCNT concentrations (>1.0 µg/cm2) exhibit frequency independent conductivity over the entire frequency range (up to 1 MHz), indicating that conduction in these devices is due to direct contact between the CNTs in the network. A simple single-relaxation time electrical equivalent circuit with an effective resistance and capacitance is used to describe the device performance. The electrical noise measurements on devices with different MWCNT packing densities exhibit bias-dependent low-frequency 1/f noise, attributed to resistance fluctuations.
Highlights
With growing demands for miniaturization and for small electronic devices with many integrated functionalities, there have been systematic studies on several nanoscale systems, including research on conducting thin films of carbon nanotubes (CNTs) [1,2]
In our previous work [25], the direct current (DC) resistance of a thin multiwall carbon nanotube (MWCNT) network was shown to scale with the areal mass density of MWCNTs by a power law, with a percolation exponent of 1.42 and a percolation threshold of 0.12 μg/cm2
The impedance spectra of a network of MWCNTs are investigated as a function of the concentration of CNTs in the device
Summary
With growing demands for miniaturization and for small electronic devices with many integrated functionalities, there have been systematic studies on several nanoscale systems, including research on conducting thin films of carbon nanotubes (CNTs) [1,2]. High infrared bolometric photoresponse has been observed in multiwall carbon nanotube (MWCNT) films at room temperature [5,6]. Due to their excellent electrical and mechanical properties another promising application has been the integration of CNTs into micro-electromechanical system (MEMS) devices [7,8]. CNTs incorporated into polymer matrices have resulted in nano-composites with enhanced mechanical, electrical and sensing properties [9,10,11,12] This is why most of the research has focused on CNT-based nano-composites where, at a critical volume fraction (percolation threshold), there is a steep increase in electrical conductivity. Multi-walled CNTs (MWCNTs) are favored since, while single-walled CNTs (SWCNTs) can exhibit both semiconducting and metallic properties, MWCNTs are mostly metallic in character with conductivities in the range of 105 –107 S/m [15,16]
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