A Review of Carbon Nanotube Ensembles as Flexible Electronics and Advanced Packaging Materials

[+] Author and Article Information
Satish Kumar

 G. W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, 771 Ferst Drive, Atlanta, GA 30332satish.kumar@me.gatech.edu

Baratunde A. Cola, Roderick Jackson, Samuel Graham

 G. W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, 771 Ferst Drive, Atlanta, GA 30332

J. Electron. Packag 133(2), 020906 (Jun 17, 2011) (12 pages) doi:10.1115/1.4004220 History: Received October 23, 2009; Revised May 01, 2011; Published June 17, 2011; Online June 17, 2011

The exceptional electronic, thermal, mechanical, and optical characteristics of carbon nanotubes offer significant improvement in diverse applications such as flexible electronics, energy conversion, and thermal management. We present an overview of recent research on the fabrication, characterization and modeling of carbon nanotube (CNT) networks or ensembles for three emerging applications: thin-film transistors for flexible electronics, interface materials for thermal management and transparent electrodes for organic photovoltaics or light emitting diodes. Results from experimental measurements and numerical simulations to determine the electrical and thermal transport properties and characteristics of carbon nanotube networks and arrays used in the above applications are presented. The roles heterogeneous networks of semiconducting and metallic CNTs play in defining electrical, thermal, and optical characteristics of CNT ensembles are presented. We conclude with discussions on future research directions for electronics and packaging materials based on CNT ensembles.

Copyright © 2011 by American Society of Mechanical Engineers
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Figure 1

Schematic of (a) nanotube network thin-film transistor showing source, drain, gate, and channel region. (b) Channel region of thin-film transistor showing source (S), drain (D), and channel (C). The channel region is composed of a network of CNTs, Geometric parameters are also shown. LC is the length of the channel and H is the width of the transistor [36].

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Figure 2

(a) Computed conductance dependence on channel length for different densities (ρ) in the strong coupling limit (cij  = 50) compared with experimental results from Ref. [15]. For ρ = 10.0 μm−2 , Go  = 1.0 (simulation), Go  = 1.0 (experiment). For ρ = 1.35 μm−2 , Go  = 1.0 (simulation), Go  = 2.50 (experiment). The number after each curve corresponds to the value of ρ used in the simulation. The number in [ ] corresponds to ρ in experiments from Ref. [15]. (b) Dependence of conductance exponent (n) on channel length for different densities (ρ) based on (a) [44].

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Figure 3

Computed IDSVGS at VDS  = 0.1 V for different densities is compared with experimental results from Ref. [15] before the electrical breakdown of metallic tubes. Solid lines correspond to experimental results from Ref. [15] and markers correspond to computational results. The number after each curve corresponds to tube density ρ. The curve ρ = 3.5 μm−2 is shifted on the x-axis to account for charge trapping [39].

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Figure 4

Computed IDSVGS at VDS  = −10 V for different CNT-densities (ρ ∼ 1–17 μm−2 ) is compared with experimental results in Ref. [68]. The vol. % of CNT dispersions used in the experiments and the corresponding network density (ρ (μm−2 )) used in the computations are shown. Lt  = 1 μm, LC  = 20 μm, and H = 200 μm. The shift in the IDSVGS curves due to the initiation of semiconducting CNT percolation for CNT vol. % >0.2% is shown by the dashed arrow [37].

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Figure 5

(a) Schematic (not to scale) of an interface with the addition of a vertically oriented CNT array of thickness tarray [24]. (b) Buckled CNT contacting an opposing surface with its wall. As shown some CNTs do not make direct contact with the opposing surface. (c) Resistance schematic of a one-sided CNT array interface between two substrates, showing constriction resistances (Rcsi ), phonon ballistic resistances (Rbi ), and the effective resistance of the CNT array (R″array ).

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Figure 6

CNT array interface structures. (a) An example one-sided interface. (b) An example two-sided interface. (c) An example CNT-coated foil interface. (d) CNT arrays on both sides of 25 μm-thick Al foil [24].

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Figure 7

Room-temperature thermal resistances as a function of pressure. (a) One-sided CNT array interfaces. (b) Two-sided CNT array interfaces and CNT-coated foil interfaces.

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Figure 8

True contact resistances for a one-sided Si-CNT-Ag interface at 0.241 MPa measured at room temperature using a photoacoustic technique [47]

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Figure 9

Correlation between transparency and Rsh . Film transparency represented by transmittance at 520 nm. Taken from Ref. [109].

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Figure 10

Picture show vacuum filtered CNT electrode on a PET substrate (left) and an SEM image showing the details of the CNT network (right)

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Figure 11

Data showing the transmittance versus wavelength for doped and undoped SWNT electrodes. Doping was performed with thionyl chloride and nitric acid.



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