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Directed assembly of solution processed single-walled carbon nanotubes via dielectrophoresis: From aligned array to individual nanotube devices


Abstract: The authors demonstrate directed assembly of high quality solution processed single-walled carbon nanotube (SWNT) devices via ac dielectrophoresis using commercially available SWNT solutions. By controlling the shape of the electrodes, concentration of the solution, and assembly time, the authors are able to control the assembly of SWNTs from dense arrays down to individual SWNT devices. Electronic transport studies of individual SWNT devices show field effect mobilities of up to 1380 cm2/V s for semiconducting SWNTs and saturation currents of up to ∼15 μA for metallic SWNTs. The field effect mobilities are more than an order of magnitude improvement over previous solution processed individual SWNT devices and close to the theoretical limit. Field effect transistors (FET) fabricated from aligned two-dimensional arrays of SWNT show field effect mobility as high as 123 cm2/V s, which is three orders of magnitude higher than the solution processed organic FET devices. This study shows promise for commerciall...
Topics: Dielectrophoresis (51%), Nanotube (51%), Carbon nanotube (50%), Field effect (50%)

Summary (4 min read)

Introduction

  • University of Central Florida STARS Faculty Bibliography 2010s Faculty Bibliography 1-1-2010 Published by the American Vacuum Society ARTICLES YOU MAY BE INTERESTED IN Directed assembly of solution processed single-walled carbon nanotubes via dielectrophoresis: From aligned array to individual nanotube devices Paul Stokes and Saiful I. Khondakera Nanoscience Technology Center and Department of Physics, University of Central Florida, 12424 Research Parkway, Orlando, Florida 32826 Received 9 July 2010; accepted 7 September 2010; published 29 November 2010 For practical applications in nanoelectronics, it is important that SWNTs are assembled at selected positions of the circuit with high yield.
  • Catalytic particles in the solution tend to make their way into the electrode gap with the SWNTs during assembly process due to their highly conducive nature which can disrupt their device performance.

A. Electrode design and fabrication

  • Devices were fabricated on heavily doped silicon substrates capped with a thermally grown 250 nm thick SiO2 layer.
  • The electrode patterns were fabricated by a combination of optical and electron beam lithography EBL .
  • First, contact pads and electron beam markers were fabricated with optical lithography using double layer resists LOR 3A/ Shipley 1813 developing in CD26, thermal evaporation of 3 nm Cr and 50 nm Au followed by lift-off.
  • Smaller electrode patterns were fabricated with EBL using single layer PMMA resists and then developing in 1:3 methyl isobutyl ketone:isopropal alchohol MIBK:IPA .
  • The electrode patterns for the alignment of individual tubes use a pair of adjacent taper shaped electrodes with sharp tips separated by 1 m, whereas the electrode patters for aligned arrays of SWNTs were done using 200 m long parallel electrodes with 5 m spacing.

B. Solution preparation

  • The authors used three different SWNT solutions for the DEP assembly: i A homemade dimethylformamide DFM solution, ii homemade dichloroethane DCE solution, and iii already suspended, surfactant-free aqueous SWNT solution purchased from Brewer Science Inc.26.
  • The DMF-SWNT suspension was made by ultrasonically dispersing HiPCO grown SWNTs Carbon Nanotechnologies Inc. in 5 ml DMF and 1 ml trifluoroacetic acid TFA .
  • TFA was used to dissolve any unwanted catalytic particles and amorphous carbon from the bulk material.
  • After dissolving the SWNTs in DMF/TFA, the solution was centrifuged, the supernatant was decanted, and the solid is then redispersed for further dispersion/centrifugation/decantation cycles.
  • The DCE mixture was made by simply adding a very small pinch of the HiPCO SWNT soot to 4 ml of DCE and then sonicating for 5–10 min before the assembly.

C. Dielectrophoretic assembly

  • The directed assembly of SWNTs at predefined electrode positions was done in a probe station under ambient conditions.
  • A small drop of SWNT solution was cast onto the chip containing the electrode pairs.
  • The induced dipole moment of the nanotube interacting with the strong electric field causes the nanotubes to move in a translational motion along the electric field gradient.
  • Hence the authors can set the effective potential of the electrodes to = Vp-p /2 for their simulation.
  • B, Vol. 28, No. 6, Nov/Dec 2010 tor was turned off and the sample was blown dry by a stream of nitrogen gas.

A. Controlling the assembly of individual SWNTs

  • Figure 2 shows the effect of SWNT concentration on the DEP assembly using the commercial solution diluted in DI water.
  • The authors use a simultaneous deposition technique14,22 in this case, applying the ac field between source and gate for 3 min.
  • The yield for the 1000 ng/ml and 100 ng/ml concentration is 95%.
  • Approximately 10% of the diameters are greater than 3.5 nm, which is an indication of the possible presence of some double-walled nanotubes or large diameter SWNTs.
  • It can be seen here that the devices are free of bundles and catalytic particles which stems from the quality of the commercial solution.

B. Comparison of solutions

  • This is done because long trapping times are more complex to use as DMF and DCE evaporate quickly in air.
  • Figure 4 a shows a representative AFM im- age after the assembly for the DMF solution.
  • As can be clearly seen here, the resulting SWNT deposition contains a bundle and catalytic particles shown by the arrows.
  • The commercial solution turned out to be stable for months, therefore increasing the reproducibility.
  • 26 Therefore, although the DMF and DCE solutions may be optimized for further control, however, due to the reproducible and clean device assembly from the stable commercial solution, the authors only continued further investigation of the devices stemming from the commercial solution.

C. Electrical transport properties of individual nanotube devices

  • After the DEP assembly, the room temperature dc electrical transport measurements of the devices were done in a probe station using a DL instruments 1211 current preamplifier combined with a high resolution DAC card interfaced with LABVIEW.
  • After two terminal resistance measurements of the as-assembled devices, they were annealed in a tube furnace using ultrahigh purity Ar /H2 1:10 ratio/Ar:H2 at 200 °C for 1 h.
  • During cool down, the gas was left flowing until the sample reached room temperature.
  • Approximately 70% of their devices show metallic or semimetallic behavior with current on-off ratio Ion / Ioff less than 10, and 30% of the devices show semiconducting behavior with on-off ratios 10.
  • The higher percentage of metallic nanotubes during the assembly is expected since, to the first order approximation, DEP tends to attract metallic SWNTs over semiconducting SWNTs because metallic SWNTs have a higher dielectric constant.

1. Metallic nanotube device properties

  • Figure 5 b is a histogram of the contact resistance for the metallic SWNT devices before annealing and after annealing.
  • The average contact resistances before and after annealing are 100 M and 1 M , respectively.
  • The contact resistance is as low as 25 k after annealing for C6B10 Paul Stokes and Saiful I. Khondaker: Directed assembly of solution processed SWNTs C6B10 J. Vac. Sci. Technol.
  • B, Vol. 28, No. 6, Nov/Dec 2010 certain devices.
  • To characterize the quality of the metallic SWNTs and their contact, the authors measured the ID-VDS characteristics at high bias after annealing.

2. Semiconducting nanotube device properties

  • Figure 5 c shows the transfer characteristics, ID-VG, for a representative FET device at VDS=−0.1, 0.5, 1.0, and 2.0 V d 1.7 nm showing p-type transport characteristics.
  • The drain current changes by several orders of magnitude with gate voltage and maintains approximately the same off-current for each VDS.
  • The maximum mobility is 20 times higher than the highest previous reported values for other solution processed devices and close to what is expected in high quality direct growth CVD devices of similar diameter.
  • The authors speculate that the improved device performance stems from the nonexistence of residual surfactant and the cleanliness of the as-assembled devices with the absence of bundles.

D. Large area assembly and device properties

  • Large scale parallel arrays of SWNTs are of considerable interests in order to increase device to device homogeneity and their expected higher performance compared to organic electronic FETs.
  • The authors used diluted commercial solution 1 g /ml for this assembly along with parallel electrode.
  • The array contains a mixture of metallic and semiconducting SWNTs as evident in the I-VG for the asassembled device Fig. 6 b top curve where the device shows semimetallic behavior with an on-off ratio of 3.
  • After the second breakdown, the mobility reduces a small amount to 53 cm2 /V s and the on-off ratio increases to 14.
  • The devices yield median mobility values of 77, 41, and 15 cm2 /V s after the three breakdowns, respectively.

IV. CONCLUSIONS

  • The authors demonstrated directed assembly of high quality solution processed carbon nanotube devices via ac dielectrophoresis using commercially available SWNT solutions.
  • By optimizing the device design, concentration of the solution, and assembly time, the authors are able to control the assembly of SWNTs from dense arrays to clean individual devices.
  • Electronic transport measurements of individual SWNT revealed mobilities more than an order of magnitude improvement over previous solution processed individual SWNT devices and close to the theoretical limit.
  • FETs fabricated from aligned 2D arrays of SWNT show high field effect mobility, up to three orders of magnitude higher than solution processed organic FET devices.
  • This study shows promise for commercially available SWNT solution for the parallel fabrication of high quality nanoelectronic devices.

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University of Central Florida University of Central Florida
STARS STARS
Faculty Bibliography 2010s Faculty Bibliography
1-1-2010
Directed assembly of solution processed single-walled carbon Directed assembly of solution processed single-walled carbon
nanotubes via dielectrophoresis: From aligned array to individual nanotubes via dielectrophoresis: From aligned array to individual
nanotube devices nanotube devices
Paul Stokes
University of Central Florida
Saiful I. Khondaker
University of Central Florida
Find similar works at: https://stars.library.ucf.edu/facultybib2010
University of Central Florida Libraries http://library.ucf.edu
This Article is brought to you for free and open access by the Faculty Bibliography at STARS. It has been accepted for
inclusion in Faculty Bibliography 2010s by an authorized administrator of STARS. For more information, please
contact STARS@ucf.edu.
Recommended Citation Recommended Citation
Stokes, Paul and Khondaker, Saiful I., "Directed assembly of solution processed single-walled carbon
nanotubes via dielectrophoresis: From aligned array to individual nanotube devices" (2010).
Faculty
Bibliography 2010s
. 828.
https://stars.library.ucf.edu/facultybib2010/828

Directed assembly of solution processed single-walled carbon nanotubes via
dielectrophoresis: From aligned array to individual nanotube devices
Paul Stokes, and Saiful I. Khondaker
Citation: Journal of Vacuum Science & Technology B 28, C6B7 (2010); doi: 10.1116/1.3501347
View online: https://doi.org/10.1116/1.3501347
View Table of Contents: https://avs.scitation.org/toc/jvb/28/6
Published by the American Vacuum Society
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Applied Physics Letters 94, 261903 (2009); https://doi.org/10.1063/1.3151850

Directed assembly of solution processed single-walled carbon nanotubes
via dielectrophoresis: From aligned array to individual nanotube
devices
Paul Stokes and Saiful I. Khondaker
a
Nanoscience Technology Center and Department of Physics, University of Central Florida, 12424 Research
Parkway, Orlando, Florida 32826
Received 9 July 2010; accepted 7 September 2010; published 29 November 2010
The authors demonstrate directed assembly of high quality solution processed single-walled carbon
nanotube SWNT devices via ac dielectrophoresis using commercially available SWNT solutions.
By controlling the shape of the electrodes, concentration of the solution, and assembly time, the
authors are able to control the assembly of SWNTs from dense arrays down to individual SWNT
devices. Electronic transport studies of individual SWNT devices show field effect mobilities of up
to 1380 cm
2
/ V s for semiconducting SWNTs and saturation currents of up to 15
A for metallic
SWNTs. The field effect mobilities are more than an order of magnitude improvement over previous
solution processed individual SWNT devices and close to the theoretical limit. Field effect
transistors FET fabricated from aligned two-dimensional arrays of SWNT show field effect
mobility as high as 123 cm
2
/ V s, which is three orders of magnitude higher than the solution
processed organic FET devices. This study shows promise for commercially available SWNT
solution for the parallel fabrication of high quality nanoelectronic devices. © 2010 American
Vacuum Society. DOI: 10.1116/1.3501347
I. INTRODUCTION
The unique electronic properties of single-walled carbon
nanotubes SWNTs make them promising candidates for fu-
ture nanoelectronic devices.
1
For practical applications in na-
noelectronics, it is important that SWNTs are assembled at
selected positions of the circuit with high yield. Chemical
vapor deposition CVD growth of SWNTs using litho-
graphically patterned catalytic islands and then making elec-
trical contact to them has been used for the parallel fabrica-
tion of SWNT devices.
2,3
Although CVD grown SWNT has
shown good device properties, high growth temperature
900 °C is a major bottleneck to make them compatible
with current complementary metal-oxide-semiconductor
CMOS fabrication technologies.
An attractive alternative to CVD growth techniques for
the high throughput assembly of SWNT electronic devices at
selected positions of the circuit is from postsynthesis fabri-
cation using solution processed SWNTs.
4
Solution process-
ing could be advantageous due to its ease of processing at
room temperature, CMOS compatibility, and potential for
scaled up manufacturing of SWNT devices on various sub-
strates. Several assembly techniques from solution include
chemical and biological patterning,
5,6
flow assisted
alignment,
7
Langmuir–Blodgett assembly,
8
bubble blown
films,
9
contact printing,
10
spin coating assisted alignment,
11
and evaporation driven self-assembly.
12
However, most of
these techniques are used either for only large area devices or
only single nanotube devices. In addition, most of these as-
sembly techniques require postetching to remove excess
SWNTs in the circuit.
Dielectrophoresis DEP offers a convenient way in which
SWNTs can be precisely positioned from solution at room
temperature using a nonuniform ac electric field on prepat-
terned electrodes.
1324
DEP can be advantageous over other
solution processed techniques because it allows for the posi-
tioning from large areas to individual SWNTs at predefined
coordinates of the circuit and does not require the need of
postetching or transfer printing. One crucial aspect of the
DEP process is the quality of the SWNT solution. The solu-
tion should be free of catalytic particles, contain mostly in-
dividual SWNTs, and be stable for long periods of time.
Catalytic particles in the solution tend to make their way into
the electrode gap with the SWNTs during assembly process
due to their highly conducive nature which can disrupt their
device performance. Solutions containing bundles make it
difficult to only obtain individual SWNTs reproducibly into
the electrode gap as the DEP force will likely select the
larger bundles due to their higher dielectric constant and con-
ductivity. Additionally, avoiding degradation of the SWNTs
from processing is extremely important to maintain their ex-
cellent electrical properties.
25
In this article, we used a clean commercially available,
surfactant-free SWNT solution combined with the DEP tech-
nique to achieve directed assembly of high quality SWNT
devices with high yield. By optimizing the device design,
concentration of the solution, and assembly time, we are able
to control the assembly of SWNTs from large scale arrays
down to individual devices. Comparison of the assembly
from commercial solution of SWNT with other homemade
solutions in common organic solvents show that the clean
a
Author to whom correspondence should be addressed; electronic mail:
saiful@mail.ucf.edu
C6B7 C6B7J. Vac. Sci. Technol. B 286, Nov/Dec 2010 1071-1023/2010/286/C6B7/6/$30.00 ©2010 American Vacuum Society

assembly was obtained from the commercial solution. Elec-
tronic transport properties of individual semiconducting
SWNTs show field effect mobilities up to 1380 cm
2
/ V s and
saturation currents up to 15
A for metallic SWNTs. The
field effect mobilities are more than an order of magnitude
improvement over previous solution processed individual
SWNT devices and close to the theoretical limit. Addition-
ally, field effect transistors FET fabricated from aligned
two-dimensional 2D arrays of SWNT show field effect mo-
bilities as high as 123 cm
2
/ V s, which is three orders of
magnitude higher than solution processed organic FET de-
vices.
II. EXPERIMENTAL DETAILS
A. Electrode design and fabrication
Devices were fabricated on heavily doped silicon sub-
strates capped with a thermally grown 250 nm thick SiO
2
layer. The electrode patterns were fabricated by a combina-
tion of optical and electron beam lithography EBL. First,
contact pads and electron beam markers were fabricated with
optical lithography using double layer resists LOR 3A/
Shipley 1813 developing in CD26, thermal evaporation of 3
nm Cr and 50 nm Au followed by lift-off. Smaller electrode
patterns were fabricated with EBL using single layer PMMA
resists and then developing in 1:3 methyl isobutyl keto-
ne:isopropal alchohol MIBK:IPA. After defining the pat-
terns, 2 nm Cr and 25 nm thick Pd were deposited using
electron beam deposition followed by lift-off in warm ac-
etone. Pd was used because it is known to make the best
electrical contact to SWNTs.
3
Figures 1a and 1b show a
cartoon of the electrode patterns for the DEP assembly of
individual SWNTs and parallel arrays of SWNTs, respec-
tively. The electrode patterns for the alignment of individual
tubes use a pair of adjacent taper shaped electrodes with
sharp tips separated by 1
m, whereas the electrode patters
for aligned arrays of SWNTs were done using 200
m long
parallel electrodes with 5
m spacing.
B. Solution preparation
We used three different SWNT solutions for the DEP as-
sembly: i A homemade dimethylformamide DFM solu-
tion, ii homemade dichloroethane DCE solution, and iii
already suspended, surfactant-free aqueous SWNT solution
purchased from Brewer Science Inc.
26
The DMF-SWNT sus-
pension was made by ultrasonically dispersing HiPCO
grown SWNTs Carbon Nanotechnologies Inc. in 5ml
DMF and 1 ml trifluoroacetic acid TFA. TFA was used to
dissolve any unwanted catalytic particles and amorphous car-
bon from the bulk material. After dissolving the SWNTs in
DMF/TFA, the solution was centrifuged, the supernatant was
decanted, and the solid is then redispersed for further
dispersion/centrifugation/decantation cycles. The final solu-
tion was diluted until it became clear and then sonicated for
several minutes before assembly. The DCE mixture was
made by simply adding a very small pinch of the HiPCO
SWNT soot to 4 ml of DCE and then sonicating for
5 10 min before the assembly. The commercial solution
has an original SWNT concentration of 50
g/ ml and was
diluted using de-ionized DI water to a desired concentra-
tion.
C. Dielectrophoretic assembly
The directed assembly of SWNTs at predefined electrode
positions was done in a probe station under ambient condi-
tions. A small drop of SWNT solution was cast onto the chip
containing the electrode pairs. An ac voltage of 1 MHz,
5V
p-p
was applied using a function generator between the
source and drain electrodes or by a simultaneous deposition
technique
14,22
between source and gate to align at several
electrode pairs simultaneously. The ac voltage gives rise to a
time averaged dielectrophoretic force. For an elongated ob-
ject, it is given by F
DEP
⬀␧
m
ReK
f
E
rms
2
, K
f
=
p
m
/
m
,
and
p,m
=
p,m
i
p,m
/
, where
p
and
m
are the permit-
tivities of the nanotube and, solvent respectively, K
f
is the
Claussius–Mossotti factor,
is the conductivity, and
=2
f is the frequency of the applied ac voltage.
27
The in-
duced dipole moment of the nanotube interacting with the
strong electric field causes the nanotubes to move in a trans-
lational motion along the electric field gradient.
Figures 1c and 1d show a simulation of the electric
field around the electrode gap for the adjacent taper shaped
electrode and parallel plate electrode, respectively. The simu-
lations were done using a commercially available software
FLEX PDE assuming that the potential phasor is real and
therefore using the electrostatic form of the Laplace equation
2
=0.
14
Hence we can set the effective potential of the
electrodes to = V
p-p
/ 2 for our simulation. From Fig.
1c, it can be seen that the strongest electric field lines are
confined at the sharp tips. This increases the probability of
aligning individual SWNTs. For the parallel plate geometry,
the electric field is uniform throughout the electrode gap al-
lowing for many nanotubes to align parallel to one another
throughout the gap. After the assembly, the function genera-
FIG.1. Color online兲共a Cartoon of the electrode patterns for DEP assem-
bly of a individual SWNTs and b 2D arrays of SWNTs. 2D simulated
electric field around the electrode gap for c the taper shaped electrodes and
d parallel plate electrodes.
C6B8 Paul Stokes and Saiful I. Khondaker: Directed assembly of solution processed SWNTs C6B8
J. Vac. Sci. Technol. B, Vol. 28, No. 6, Nov/Dec 2010

tor was turned off and the sample was blown dry by a stream
of nitrogen gas.
III. RESULTS AND DISCUSSIONS
A. Controlling the assembly of individual SWNTs
Figure 2 shows the effect of SWNT concentration on the
DEP assembly using the commercial solution diluted in DI
water. We use a simultaneous deposition technique
14,22
in
this case, applying the ac field between source and gate for 3
min. Figure 2a shows an atomic force microscopy AFM
image of a device after the assembly for a SWNT concentra-
tion of 1000 ng/ml. Dilution of the solution by ten times to
100 ng/ml concentration yield less SWNTs in the gap, as
shown in Fig. 2b. It can be seen here in both cases that the
SWNTs mimic the electric field lines around the electrode
gap, as simulated in Fig. 1c. The yield for the 1000 ng/ml
and 100 ng/ml concentration is 95%. By diluting the solu-
tion to 10 ng/ml, we obtained an individual SWNT in the gap
Fig. 2c. The diameter of this individual SWNT is
2.0 nm, measured by AFM. Figure 2d shows a histogram
of 100 individual SWNTs giving an average diameter of
2.00.2 nm. Approximately 10% of the diameters are
greater than 3.5 nm, which is an indication of the possible
presence of some double-walled nanotubes or large diameter
SWNTs.
28
The total yield of individual SWNTs at low con-
centration is 20% on average and as high as 35% for a
single chip. Figure 3 shows a number of SEM images of
individual nanotubes assembled by this technique. It can be
seen here that the devices are free of bundles and catalytic
particles which stems from the quality of the commercial
solution.
B. Comparison of solutions
We investigated the effect of the different solutions at low
concentration 共⬃10 ng/ ml on the DEP assembly. In con-
trast to the commercial solution in water, for the DMF and
DCE solutions, we apply the ac voltage between one pair at
a time for 5 s. This is done because long trapping times
are more complex to use as DMF and DCE evaporate
quickly in air. Figure 4a shows a representative AFM im-
age after the assembly for the DMF solution. As can be
clearly seen here, the resulting SWNT deposition contains a
bundle and catalytic particles shown by the arrows. At cer-
tain areas along the SWNT, the diameter is as large as 30–40
nm. Figure 4b shows the representative AFM image of a
device after assembling the SWNTs using DCE. The result-
ing device also contains catalytic particles near the electrode
tip on the right and shows diameters up to 10 nm along the
SWNT. Figure 4c shows an AFM image of a device after
assembly by using the Brewer Science SWNT solution. It is
clear from the AFM image that the SWNT is individual and
does not contain any catalytic particles. The commercial so-
lution turned out to be stable for months, therefore increasing
the reproducibility. For the DCE solution we were able to
assemble 10 individual SWNT devices out of 80 tries,
however, all of them contained catalytic particles with
diameter10 nm attached to the tubes. Another problem
that arises when using DCE is that it evaporates in air very
quickly, it is highly toxic, volatile, and did not remain stable
for more than a few hours. In the DMF case, the solutions
also only remained stable for a short period of time and the
results often came with larger diameter bundles 15 nm out
of 50 tries.
As can be concluded here, the commercial solution
yielded the best results for the assembly of clean and indi-
vidual SWNT devices. The good results from the commercial
solution are due to several reasons. First, its very low density
of impurity particles less than 50 ppb
26
is particularly ad-
vantageous in the DEP process because catalytic particles in
the solution tend to make their way into the electrode gap
during DEP due to their high conductivity. This is displayed
FIG.2. Color online AFM image of nanotubes assembled between the
electrodes with SWNT concentrations of a 1000 ng/ml b 100 ng/ml, and
c 10 ng/ml in the solution. Scale bar: 1
m in all images. d Histogram of
diameters for over 100 nanotube devices.
FIG.3. 关共a-l兲兴 SEMs of several individual SWNT assembled via DEP from
commercial solution at a concentration of 10 ng/ml. Gap between the
electrodes is 1
m.
FIG.4. Color online Representative AFM images of SWNTs assembled via
DEP a from DMF solution, b from DCE solution, and c the Brewer
Science solution.
C6B9 Paul Stokes and Saiful I. Khondaker: Directed assembly of solution processed SWNTs C6B9
JVSTB-MicroelectronicsandNanometer Structures

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39 citations



Journal ArticleDOI
Abstract: We report strategies to achieve both high assembly yield of carbon nanotubes at selected positions of the circuit via dielectrophoresis (DEP) and field effect transistor (FET) yield using an aqueous solution of semiconducting-enriched single-walled carbon nanotubes (s-SWNTs). When the DEP parameters were optimized for the assembly of individual s-SWNTs, 97% of the devices showed FET behavior with a maximum mobility of 210 cm2 V−1 s−1, on–off current ratio ∼ 106 and on-conductance up to 3 µS, but with an assembly yield of only 33%. As the DEP parameters were optimized so that one to five s-SWNTs are connected per electrode pair, the assembly yield was almost 90%, with ∼90% of these assembled devices demonstrating FET behavior. Further optimization gave an assembly yield of 100% with up to 10 SWNTs per site, but with a reduced FET yield of 59%. Improved FET performance including higher current on–off ratio and high switching speed were obtained by integrating a local Al2O3 gate to the device. Our 90% FET with 90% assembly yield is the highest reported so far for carbon nanotube devices. Our study provides a pathway which could become a general approach for the high yield fabrication of complementary metal oxide semiconductor (CMOS)-compatible carbon nanotube FETs.

20 citations


References
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Journal ArticleDOI
Ali Javey1, Jing Guo2, Qian Wang1, Mark Lundstrom2  +1 moreInstitutions (2)
07 Aug 2003-Nature
TL;DR: It is shown that contacting semiconducting single-walled nanotubes by palladium, a noble metal with high work function and good wetting interactions with nanotube, greatly reduces or eliminates the barriers for transport through the valence band of nanot tubes.
Abstract: A common feature of the single-walled carbon-nanotube field-effect transistors fabricated to date has been the presence of a Schottky barrier at the nanotube–metal junctions1,2,3. These energy barriers severely limit transistor conductance in the ‘ON’ state, and reduce the current delivery capability—a key determinant of device performance. Here we show that contacting semiconducting single-walled nanotubes by palladium, a noble metal with high work function and good wetting interactions with nanotubes, greatly reduces or eliminates the barriers for transport through the valence band of nanotubes. In situ modification of the electrode work function by hydrogen is carried out to shed light on the nature of the contacts. With Pd contacts, the ‘ON’ states of semiconducting nanotubes can behave like ohmically contacted ballistic metallic tubes, exhibiting room-temperature conductance near the ballistic transport limit of 4e2/h (refs 4–6), high current-carrying capability (∼25 µA per tube), and Fabry–Perot interferences5 at low temperatures. Under high voltage operation, the current saturation appears to be set by backscattering of the charge carriers by optical phonons. High-performance ballistic nanotube field-effect transistors with zero or slightly negative Schottky barriers are thus realized.

3,008 citations


Journal ArticleDOI
TL;DR: This work reviews the progress that has been made with carbon nanotubes and, more recently, graphene layers and nanoribbons and suggests that it could be possible to make both electronic and optoelectronic devices from the same material.
Abstract: The semiconductor industry has been able to improve the performance of electronic systems for more than four decades by making ever-smaller devices. However, this approach will soon encounter both scientific and technical limits, which is why the industry is exploring a number of alternative device technologies. Here we review the progress that has been made with carbon nanotubes and, more recently, graphene layers and nanoribbons. Field-effect transistors based on semiconductor nanotubes and graphene nanoribbons have already been demonstrated, and metallic nanotubes could be used as high-performance interconnects. Moreover, owing to the excellent optical properties of nanotubes it could be possible to make both electronic and optoelectronic devices from the same material.

2,184 citations


Journal ArticleDOI
27 Apr 2001-Science
TL;DR: A simple and reliable method for selectively removing single carbon shells from MWNTs and SWNT ropes to tailor the properties of these composite nanotubes and to directly address the issue of multiple-shell transport.
Abstract: Carbon nanotubes display either metallic or semiconducting properties. Both large, multiwalled nanotubes (MWNTs), with many concentric carbon shells, and bundles or “ropes” of aligned single-walled nanotubes (SWNTs), are complex composite conductors that incorporate many weakly coupled nanotubes that each have a different electronic structure. Here we demonstrate a simple and reliable method for selectively removing single carbon shells from MWNTs and SWNT ropes to tailor the properties of these composite nanotubes. We can remove shells of MWNTs stepwise and individually characterize the different shells. By choosing among the shells, we can convert a MWNT into either a metallic or a semiconducting conductor, as well as directly address the issue of multiple-shell transport. With SWNT ropes, similar selectivity allows us to generate entire arrays of nanoscale field-effect transistors based solely on the fraction of semiconducting SWNTs.

1,794 citations


Journal ArticleDOI
Seong Jun Kang1, Coskun Kocabas1, Taner Ozel1, Moonsub Shim1  +4 moreInstitutions (3)
TL;DR: Dense, perfectly aligned arrays of long, perfectly linear SWNTs are reported as an effective thin-film semiconductor suitable for integration into transistors and other classes of electronic devices, representing a route to large-scale integrated nanotube electronics.
Abstract: †Single-walled carbon nanotubes (SWNTs) have many exceptional electronic properties. Realizing the full potential of SWNTs in realistic electronic systems requires a scalable approach to device and circuit integration. We report the use of dense, perfectly aligned arrays of long, perfectly linear SWNTs as an effective thin-film semiconductor suitable for integration into transistors and other classes of electronic devices. The large number of SWNTs enable excellent device-level performance characteristics and good device-to-device uniformity, even with SWNTs that are electronically heterogeneous. Measurements on p- and n-channel transistors that involve as many as 2,100 SWNTs reveal device-level mobilities and scaled transconductances approaching 1,000 cm 2 V 21 s 21 and 3,000 S m 21 , respectively, and with current outputs of up to 1 A in devices that use interdigitated electrodes. PMOS and CMOS logic gates and mechanically flexible transistors on plastic provide examples of devices that can be formed with this approach. Collectively, these results may represent a route to large-scale integrated nanotube electronics.

1,129 citations


Journal ArticleDOI
Kinneret Keren1, Rotem S. Berman1, E. I. Buchstab1, Uri Sivan1  +1 moreInstitutions (1)
21 Nov 2003-Science
TL;DR: Using a scheme based on recognition between molecular building blocks, the realization of a self-assembled carbon nanotube field-effect transistor operating at room temperature is reported.
Abstract: The combination of their electronic properties and dimensions makes carbon nanotubes ideal building blocks for molecular electronics. However, the advancement of carbon nanotube-based electronics requires assembly strategies that allow their precise localization and interconnection. Using a scheme based on recognition between molecular building blocks, we report the realization of a self-assembled carbon nanotube field-effect transistor operating at room temperature. A DNA scaffold molecule provides the address for precise localization of a semiconducting single-wall carbon nanotube as well as the template for the extended metallic wires contacting it.

785 citations


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