We report on high quality individual solution processed single-walled carbon nanotube (SWNT) field effect transistors assembled from a commercial surfactant free solution via dielectrophoresis. The devices show field effect mobilities up to 1380 cm(2)/V s and on-state conductance up to 6 mu S. The mobility values are an order of magnitude improvement over previous solution processed SWNT devices and close to the theoretical limit. These results demonstrate that high quality SWNT devices can be obtained from solution processing and will have significant impact in high yield fabrication of SWNT nanoelectronic devices

Khondaker, Saiful I.

Stokes, Paul

English

University of Central Florida (UCF): STARS (Showcase of Text, Archives, Research & Scholarship)

University of Central Florida STARS Faculty Bibliography 2010s Faculty Bibliography 1-1-2010 High quality solution processed carbon nanotube transistors assembled by dielectrophoresis 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 Stokes, Paul and Khondaker, Saiful I., "High quality solution processed carbon nanotube transistors assembled by dielectrophoresis" (2010). Faculty Bibliography 2010s. 826. https://stars.library.ucf.edu/facultybib2010/826 Appl. Phys. Lett. 96, 083110 (2010); https://doi.org/10.1063/1.3327521 96, 083110© 2010 American Institute of Physics.High quality solution processed carbonnanotube transistors assembled bydielectrophoresisCite as: Appl. Phys. Lett. 96, 083110 (2010); https://doi.org/10.1063/1.3327521Submitted: 08 December 2009 . Accepted: 24 January 2010 . Published Online: 25 February 2010Paul Stokes, and Saiful I. KhondakerARTICLES YOU MAY BE INTERESTED INSolution processed large area field effect transistors from dielectrophoreticly aligned arraysof carbon nanotubesApplied Physics Letters 94, 113104 (2009); https://doi.org/10.1063/1.3100197Directed assembly of solution processed single-walled carbon nanotubes viadielectrophoresis: From aligned array to individual nanotube devicesJournal of Vacuum Science & Technology B 28, C6B7 (2010); https://doi.org/10.1116/1.3501347Single- and multi-wall carbon nanotube field-effect transistorsApplied Physics Letters 73, 2447 (1998); https://doi.org/10.1063/1.122477High quality solution processed carbon nanotube transistors assembledby dielectrophoresisPaul Stokes and Saiful I. KhondakeraDepartment of Physics and Nanoscience Technology Center, University of Central Florida,12424 Research Parkway, Orlando, Florida 32826, USAReceived 8 December 2009; accepted 24 January 2010; published online 25 February 2010We report on high quality individual solution processed single-walled carbon nanotube SWNTfield effect transistors assembled from a commercial surfactant free solution via dielectrophoresis.The devices show field effect mobilities up to 1380 cm2 /V s and on-state conductance up to 6 S.The mobility values are an order of magnitude improvement over previous solution processedSWNT devices and close to the theoretical limit. These results demonstrate that high quality SWNTdevices can be obtained from solution processing and will have significant impact in high yieldfabrication of SWNT nanoelectronic devices. © 2010 American Institute of Physics.doi:10.1063/1.3327521The exceptional electronic properties of single-walledcarbon nanotubes SWNTs make them promising buildingblocks for future nanoelectronic devices.1 For the fabricationof high quality devices, clean and defect-free SWNTs aredesired. High temperature growth of SWNTs directly on thesubstrate via chemical vapor deposition CVD has been themost widely used technique to achieve high quality SWNTdevices. Assembly of SWNT devices by CVD are typicallydone by randomly dispersed catalyst or patterning catalyticislands for which the later allows for parallel assembly ofSWNT devices at selected position of the circuit directgrowth method.2 Following growth at 900 C, electricalcontact to the SWNT are made without further possessing.Such devices have shown excellent field effect transistorFET properties with typical mobility values ranging from1000 to 10 000 cm2 /V s depending upon the diameter3and conductance approaching the ballistic limit G=4e2 /h155 S, or R6.5 k.4,5 Although high quality deviceshave been obtained using direct growth CVD method,however high growth temperatures 900 °C is a majorbottleneck to make them compatible with current comple-mentary metal-oxide-semiconductor CMOS fabricationtechnologies.Post synthesis fabrication techniques from solution pro-cessed SWNTs offers an attractive alternative to high tem-perature growth for the parallel assembly of electronic de-vices due to the ease of processing at room temperature aswell as compatibility with CMOS technology and varioussubstrates including plastics.6 It is however, generally be-lieved that solution processing techniques such as purifica-tion with acids and intense ultrasonication to create stablesuspension can introduce defects and degrade the intrinsicelectrical properties of SWNTs which in turn could limittheir application in nanoelectronic devices. As a result therehas been tremendous effort and continuous progress in pro-ducing high quality SWNT stable solutions and effort tominimize degradation.7–9 This has led to the sorting of me-tallic and semiconducting SWNTs,10 and the commercializa-tion of electronic grade SWNT solutions.11 Despite these ef-forts, the reported device characteristics of solutionprocessed SWNTs are still far from their performance limit.Previous studies of Vijayaraghavan et al.12 found an averageon-state conductance Gon0.2 S for semiconductingSWNTs and Burg et al.13 reported average on-off ratios of 80but did not report mobility values. Kim et al.14 has found amobility of 19.4 cm2 /V s on average for individual semi-conducting SWNTs by density gradient techniques. Wang etal.15 used dip-pen lithography to fabricate individual SWNTdevices from solution and found a mobility of 67 cm2 /V s.In comparison to devices fabricated by direct growth methodusing CVD, these reported device properties of solution pro-cessed SWNTs are much inferior and calls for further im-provement.Here, we report on considerably improved device qualityof individual solution processed SWNT FETs from a com-mercially available surfactant-free solution. IndividualSWNTs were assembled between 1 m spaced Pd sourceand drain electrodes DEs using ac dielectrophoresis DEP.The semiconducting devices show on-state conductancevalues up to 6 S and field effect mobilities as high as1380 cm2 /V s. The maximum mobility value approachesthe theoretical performance limit for clean SWNTs and boththe on-state conductance and mobility are more than an orderof magnitude improvement from previous solution processedSWNT devices. Raman spectroscopy done on individualSWNT devices show the absence of defect related D-band.The electrical properties in combination with Raman spec-troscopy are indication of high quality SWNT devices. Thisstudy shows promise for the use of solution processedSWNTs for high performance nanoelectronics devices.The devices are fabricated on highly doped Si substrateswith a 250 nm thick SiO2 caped layer. An array of taperedshape, source and DE patterns with 1 m spacing were de-fined with electron beam lithography and electron beamdeposition of 2 nm Cr for a sticking layer and 25 nm thick Pdfollowed by lift-off. Pd is used because it is known to makethe best contact to SWNTs.5 The assembly is done in a probestation under ambient conditions and is carried out as fol-lows. A stable, surfactant-free solution of SWNT was ob-tained from Brewer Science shelf life six months11 that hada concentration of SWNTs 50 g /ml. The solution con-aAuthor to whom correspondence should be addressed. Electronic mail:saiful@mail.ucf.edu.APPLIED PHYSICS LETTERS 96, 083110 20100003-6951/2010/968/083110/3/$30.00 © 2010 American Institute of Physics96, 083110-1sists of mostly individual SWNTs and is free of catalyticparticles. The average length of the SWNTs was 1–2 mdetermined by scanning electron microscopy SEM. Afterdilution of the solution to 10 ng /ml in de-ionized water, a3 L drop is cast onto the electrode array. Figure 1a showsa three-dimensional cartoon of the assembly setup wherewe apply the ac voltage 1 MHz, 5 Vp-p between the com-mon source electrode SE and gate G electrode for 3 min.This allows for each DE to become capacitivly coupled tothe gate electrode and obtain a similar potential as the gate.Therefore at each source and DE pair there is a potentialdifference allowing for the alignment of many SWNTssimultaneously.12 Figure 1b shows a SEM image of an in-dividual SWNT assembled between the source and DEs fol-lowing the assembly. The total yield of individual SWNTsis 20% on average and as high as 35% for a single chip,which is consistent with other similar DEP studies.13,16 Fig-ure 1c shows a representative atomic force microscopyAFM image of the same device in Fig. 1b. Figure 1dshows the corresponding height profile for which we mea-sure a diameter d of 1.7 nm. The average diameter of theSWNTs for all of our devices was 1.50.2 nm. After theassembly the devices were annealed in forming gas Ar /H2at 200 C for 1 h to reduce the contact resistance.Electrical measurements were performed using a DL In-struments 1211 current preamplifier combined with a highresolution DAC card interfaced with LABVIEW. Figure 1eshows a cartoon of the measurement setup where we use thehighly doped Si as a back gate. We measured a total of 120individual SWNT devices. Approximately 70% of the de-vices show metallic or semimetallic behavior i.e., less thanone order of magnitude change in current ID as a functionof gate voltage VG and 30% of the devices show semicon-ducting behavior one or more orders of magnitude change inID as a function of VG. See supplementary information re-garding the DEP assembly of metallic and semiconductingSWNTs.17 Here, we present FET device properties of thesemiconducting SWNTs.Figure 2a shows transfer characteristics, ID-VG, for arepresentative FET device at VDS=−0.1, 0.5, 1.0, and2.0 V d1.7 nm showing p-type transport characteris-tics. The drain current changes by several orders of magni-tude with gate voltage and maintains approximately thesame on-off ratio Ion / Ioff for each VDS. For example, atVDS=−1.0 V, the on-off ratio is 3.6104 Ioff−70 pAand Ion−2.5 A. The linear conductance in the on-stateGon= Ion /VDS is 2.5 S at VDS=−1.0 V. In Fig. 2b weplot IDS versus VDS up to the saturation regime at differentgate voltages from 10 to 10 V, bottom to top. Outputcurrents are as high as 7 A, comparable to Pd contactedCVD SWNTs of similar diameter, directly grown on thesubstrate.18 We note that the ID-VDS characteristics showslightly nonlinear behavior at low VDS, which is an indicationof a small Schottky barrier.5 Work is in progress for thefurther optimization of the contact. The field effect mobilitywas calculated from the linear regime in Fig. 2a from = L2 /CGVDSdID /dVG, where the gate capacitance isCG= 2L / ln2h /r, L is the length of the channel, =3.90 is the dielectric constant for SiO2, h is the thicknessof the oxide, and r is the radius of the CNT,18 anddID /dVG=gm is the transconductance. We find gm0.06,0.30, 0.57, and 1.15 S at VDS=−0.1, 0.5, 1.0, and 2.0V, respectively. Setting r=0.85 nm gives a mobility of 157, 172, 163, and 164 cm2 /V s, respectively, indicatingthe mobility values are relatively constant at each value ofVDS see supporting information for additional mobility cal-culations for a few other devices17.Figure 3a shows a scatter plot of the mobility versusthe on-state conductance for all 35 devices that we measuredFIG. 1. Color online a Schematic of the electrode array and DEP assem-bly setup. b Representative SEM image of an individual SWNT betweensource s and drain d electrodes. Scale bar: 500 nm. c AFM image of thesame SWNT in b. Scale bar: 500 nm. d Height profile of the SWNTshowing a diameter of 1.7 nm. e Schematic diagram of device geometryand electronic transport measurement setup.FIG. 2. Color online a Transfer characteristics of a representative SWNTFET device d1.7 nm at VDS=−0.1, 0.5, 1.0, and 2.0 V. b Outputcharacteristics showing currents up to 7 A in the saturation regime.FIG. 3. Color online a Scatter plot of mobility vs on-conductance for 35FET devices. The median values of mobility and on-conductance are200 cm2 /V s and 2.2 S, respectively. b ID vs VG at VDS=−0.1 V forour highest performance FET device d1.3 nm. Inset: Mobility vs gatevoltage showing a peak mobility value of 1380 cm2 /V s. c Representa-tive Raman spectroscopy of an individual SWNT device.083110-2 P. Stokes and S. I. Khondaker Appl. Phys. Lett. 96, 083110 2010for this study taken at VDS=−0.1 V. We obtain a medianon-state conductance and mobility of 2.2 S and200 cm2 /V s, respectively. These parameters are a largeimprovement from previous studies. This is more clearlyseen in Table I where we list several recent reported valuesfor on-state conductance and mobility for solution processeddevices, and one direct growth CVD devices. Note that allquoted solution processed devices are from stable SWNTsuspensions. It can be clearly seen that the median on-stateconductance is an order of magnitude higher than previousmedian values reported by Vijayaraghavan et al.12 Our aver-age mobility values are also an order of magnitude higherthan previous studies by Kim et al.14 and 3 times higherthan previous report of Wang et al.15In Fig. 3b we show a plot of ID versus VG atVDS=−0.1 V for our highest mobility SWNT-FET deviced1.3 nm. The on-state conductance for this device is6 S. Inset of Fig. 3b shows a plot of the calculatedmobility versus gate voltage with r0.65 nm and gm0.45 S. We find that the peak mobility for this deviceis 1380 cm2 /V s. Comparing with the theoretical limitat room temperature for clean SWNTs,3,19 peak1000 cm2 /V s dnm2 where d is the diameter of thetube, we find peak1700 cm2 /V s, which is reasonablyclose to the experimental value indicating that this device isbeing pushed close to its performance limit. This deviceshows significantly better properties than the best reportedsamples from Table I. Our highest value of Gon is six timeshigher than the highest value found in Ref. 12. The maxi-mum mobility is 20 times higher than the highest previousreported values and close to what is expected in high qualitydirect growth CVD devices of similar diameter.We speculate that the improved device performancestems from the nonexistence of residual surfactant and thecleanliness of the as-assembled devices with the absence ofbundles. We verified the cleanliness of the SWNT devices byRaman spectroscopy. We used a Renishaw inVia micro-Raman spectrometer with 514 nm excitation, 1 m spotsize and 1 mW power. Figure 3c shows representativeRaman spectra near the G-band mode which is clearlyobserved at 1570 cm−1. Note the absence of the defectinduced D-band typically observed at 1350 cm−1. Themissing D-band observation indicates low density of defectsites20,21 and is consistent with high quality devices reportedhere.In conclusion, we have shown improved device perfor-mance of individual SWNT FETs assembled by DEP from asurfactant free commercial solution. The devices show a me-dian on on-state conductance of 2.2 S with a maximum of6 S while the median field effect mobility is 200 cm2 /V swith a maximum of 1380 cm2 /V s, approaching the perfor-mance limit. The absence of the D-band in the Raman spec-troscopy measurements demonstrates that the SWNTs have alow density of defects further verifying high quality device.This study show promise for solution processed SWNTs tobe viable for the parallel fabrication of high quality CMOScompatible nanoelectronic devices.This work was supported by U.S. National ScienceFoundation under Grant No. ECCS-0748091 CAREER.1P. Avouris, Z. H. Chen, and V. Perebeinos, Nat. Nanotechnol. 2, 6052007.2A. Javey, Q. Wang, A. Ural, Y. Li, and H. Dai, Nano Lett. 2, 929 2002.3X. Zhou, J.-Y. Park, S. Huang, J. Liu, and P. L. McEuen, Phys. Rev. Lett.95, 146805 2005.4D. Mann, A. Javey, J. Kong, Q. Wang, and H. Dai, Nano Lett. 3, 15412003.5A. Javey, J. Guo, Q. Wang, M. Lundstrom, and H. Dai, Nature London424, 654 2003.6L. Huang, Z. Jia, and S. O’Brien, J. Mater. Chem. 17, 3863 2007.7M. J. O’Connell, S. M. Bachilo, C. B. Huffman, V. C. Moore, M. S.Strano, E. H. Haroz, K. L. Rialon, P. J. Boul, W. H. Noon, C. Kittrell, J.Ma, R. H. Hauge, R. B. Weisman, and R. E. Smalley, Science 297, 5932002.8M. C. Hersam, Nat. Nanotechnol. 3, 387 2008.9M. C. LeMieux, M. Roberts, S. Barman, Y. W. Jin, J. M. Kim, and Z. Bao,Science 321, 101 2008.10M. S. Arnold, A. A. Green, J. F. Hulvat, S. I. Stupp, and M. C. Hersam,Nat. Nanotechnol. 1, 60 2006.11See http://www.brewerscience.com for more information about the com-mercially available SWNT solution.12A. Vijayaraghavan, S. Blatt, D. Weissenberger, M. Oron-Carl, F. Hennrich,D. Gerthsen, H. Hahn, and R. Krupke, Nano Lett. 7, 1556 2007.13B. R. Burg, J. Schneider, M. Muoth, L. Durrer, T. Helbling, N. C.Schirmer, T. Schwamb, C. Hierold, and D. Poulikakos, Langmuir 25,7778 2009.14W. J. Kim, C. Y. Lee, K. P. O’Brien, J. J. Plombon, J. M. Blackwell, andM. S. Strano, J. Am. Chem. Soc. 131, 3128 2009.15W. M. Wang, M. C. LeMieux, S. Selvarasah, M. R. Dokmeci, and Z. Bao,ACS Nano 3, 3543 2009.16L. F. Dong, V. Chirayos, J. Bush, J. Jiao, V. M. Dubin, R. V. Chebian, Y.Ono, J. F. Conley, Jr., and B. D. Ulrich, J. Phys. Chem. B 109, 131482005.17See supplementary material at http://dx.doi.org/10.1063/1.3327521 formobility calculations of a few other devices and discussion regarding theassembly of metallic and semiconducting SWNTs.18W. Kim, A. Javey, R. Tu, J. Cao, Q. Wang, and H. Dai, Appl. Phys. Lett.87, 173101 2005.19M. J. Biercuk, S. Ilani, C. M. Marcus, and P. L. McEuen, Top. Appl. Phys.111, 455 2008.20S. K. Doorn, L. Zheng, M. J. O’Connell, Y. Zhu, S. Huang, and J. Liu, J.Phys. Chem. B 109, 3751 2005.21A. W. Bushmaker, V. V. Deshpande, S. Hsieh, M. W. Bockrath, and S. B.Cronin, Phys. Rev. Lett. 103, 067401 2009.TABLE I. Comparison of some recent SWNT solution processed deviceparameters, this work, and one CVD SWNT made by direct growth methodsN/R: Not reported.FabricationmethodOn-state conductanceSMobilitycm2 /V s Ref.DEP Median: 2.2 Median: 200 This workaMax: 6.0 Max: 1380DEP Median: 0.2 N/R 12aMax: 1.0Drop cast N/R Median: 19.4 14Max: 60Drop cast/dip pen N/R 67b 15CVD 1.5c 2500 c 3a1 m long devices.bNot indicated whether this is maximum or a typical value.c1.5 nm diameter SWNT 10 m long.083110-3 P. Stokes and S. I. Khondaker Appl. Phys. Lett. 96, 083110 2010

High quality solution processed carbon nanotube transistors assembled by dielectrophoresis

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High quality solution processed carbon nanotube transistors assembled by dielectrophoresis

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