Semiconductive properties of DNA-based materials

Semiconductive properties of DNA-based materials Fahima Ouchena, Song Kima, Guru Subramanyamb, Perry Yanneyc, Liming Daid, Rajesh Naika and James Grotea a

Air Force Research Laboratory, Materials and Manufacturing Directorate, Wright-Patterson Air Force Base, OH 45433 b Department of Electrical and Computer Engineering, University of Dayton, 300 College Park, Dayton, OH, 45469 c Department of Electro-Optics, University of Dayton, 300 College Park, Dayton, OH, 45469 d Department of Materials Science and Engineering, University of Dayton, 300 College Park, Dayton, OH, 45469

ABSTRACT Deoxyribonucleic acid (DNA)-based biopolymers posses unique electronic and self assembly properties that render them suitable organic semiconductors for organic field effect transistors. Doping DNA molecules with conductive guests has resulted in a significant decrease of the overall resistivity of the blend with effective free charge carrier mobilities comparable to other conductive polymers such as pentacene and poly(3-hexylthiophene) (P3HT). In this paper we discuss doping DNA with single wall carbon nanotubes (SWCNTs) and transistor behavior. Keywords: Deoxyribonucleic acid, DNA, single walled carbon nanotube, SWCNT, organic field effect transistors.

1. INTRODUCTION Dexyribonucleic acid (DNA) has a unique molecular architecture, well suited for bioinspired nanotechnology and nanostructures with potential applications ranging from electronic devices to electrochemical biosensors, which have been previously reported.1,2,3 However, despite the increasing interest for new application, the level and type of conductivity exhibited by DNA remains at the center of debate, with contradictory results on the transport mechanism in these molecules.4 The measured conductivity of DNA molecules can also depend on many factors including, but not limited to, the interaction with the substrate surface, their structure, purity and the chemical environment surrounding them. We have found that molecular weight effects the electrical resistivity of DNA. The lower the moleclar weight Organic field effect transistors (OFETs) have received much attention lately for their potential applications in organic displays,5,6 complementary circuits7,8 and all-polymer integrated circuits.9,10 Although the best organicbased circuits11 have been prepared from vacuum-deposited Pentacene, room temperature, solution-based processing would be better suited for low-cost fabrication. In addition, in order to compete with inorganic based devices, charge carrier mobilities need to increase significantly and the cost of polymer precursors must be reduced significantly. Because of its unique electronic and self assembly properties and abundance, DNA is being investigated as an alternative for high-performance, low cost, room temperature fabricated devices. The introduction of conductive polymer, carbon nanoparticle and metallic nanoparticle guests into the DNA matrix is the approach we have taken in an attempt to modify the electrical resistivity, charge carrier density, charge carrier mobility and, potentially, the overall transport properties and to render a composite with some level of “tunability” through the adjustment of the blending level. Optical Materials in Defence Systems Technology V, edited by James G. Grote, Francois Kajzar, Mikael Lindgren, Proc. of SPIE Vol. 7118, 71180M © 2008 SPIE · CCC code: 0277-786X/08/$18 · doi: 10.1117/12.801700 Proc. of SPIE Vol. 7118 71180M-1 2008 SPIE Digital Library -- Subscriber Archive Copy

2. DNA BASED BLENDS: MATERIAL PROCESSING 2.1 DNA-CTMA The DNA used for this study was obtained from the Chitose Institute of Science and Technology. It is derived from salmon milt and roe sacs, purified to 98% with protein content reduced to 2%. The purified DNA received has an average molecular weight above 8 million Daltons (Da). Lower molecular weights are achieved using a mechanical sonication process. Molecular weights as low as 200KDa have been achieved through sonication. The processing of DNA into material suitable for device fabrication requires complexation with a cationic surfactant (hexadecyl trimethylamonium chloride (CTMA).12 The DNA-CTMA complex is water insoluble, soluble in alcohols or a chloroform/alcohol blend. Preliminary studies of the electrical properties of “solid state” thin films of DNA-CTMA show bulk resistivities as high as 1016 Ω-cm at room temperature for 8 MDa molecular weight DNA to 1012 Ω-cm at room temperature for 200KDa molecular weight DNA.13 The measured dielectric constant of DNA-CTMA thin films is ε = 7.8 (εSiO2 = 3.3). Using 8MDa DNA-CTMA as a gate insulator in a Pentacene based OFET led to a 10X decrease in gate voltage applied to modulate the source-drain current in comparison to a silicon dioxide gate.14 Thin films of 200KDa DNA-CTMA, deposited by both spinning and thermal evaporation techniques, have also been used as electron blocking layers in organic light emitting diode (OLEDs), where a 10X increase in OLED efficiency has been reported.15

2.2 DNA-SWCNT-CTMA Previously reported was a semiconductive biopolymer formed by precipitating an aqueous dispersion of poly(3,4ethylenedioxythiophene)poly(styrenesulfonate) (PEDOT:PSS) into sonicated purified DNA dissolved in water with CTMA added to the DNA-PEDOT:PSS solution to form a water-insoluble complex DNA-PEDOT:PSS-CTMA. OFETs using a DNA-PEDOT:PSS-CTMA semiconductive region with a doping level of 36% PEDOT:PSS to DNA, were comparable in performance to OFETs using a P3HT semiconductive region.16(SPIE O&P16) For processing single wall carbon nanotubes (SWNT) into DNA, we first obtained the SWNTs from HipCo, then functionalized (oxidized) following the previously established protocol.17 HipCo SWNTs were sonicated in a 3:1 (volume/volume) mixture of HNO3 and H2SO4 for 4hrs at 70oC, were filtered, washed copiously with deionized water until the pH of the filtrated water reached 7 and then dried overnight under vacuum. Two methods were employed to prepare the DNA-SWNT-CTMA. Method 1: 2wt% of the processed SWNTs were blended with purified DNA in DI water and sonicated for 50min. CTMA was then added to the DNA-SWNT complex to form DNA-SWNT-CTMA. Method 2: 2wt% of the processed SWNT were blended with CTMA in DI water and sonicated for 50min. SWNT-CTMA was then added to DNA to form DNA-SWNT-CTMA. Both DNASWNT-CTMA complexes were dissolved in butanol and centrifuged at 3,000g for 10 min and finally filtered through a 5µm pore size syringe filter.

3. DNA-BASED BLENDS: CHARACTERIZATION 3.1 Circular dichroism Circular dichroism (CD) spectra were taken on DNA-CTMA and DNA-SWCNT-CTMA (method 1 & method 2) at room temperature and are reported in Fig. 1. They were shown to exhibit the same characteristics as a CD spectrum of aqueous DNA. The decrease in intensity of the positive band (located at 275 nm) and relatively of the negative band can be attributed to the nature of the solvent used and the molarity of the samples tested. The bathochromic shift (red shift) of the CD spectra for The DNA based complexes is most likely due to the addition of the CTMA molecules on the DNA’s phosphate-backbone. This spectrum implies that DNA-CTMA retains the double helical structure of DNA at room temperature and there is not a significant DNA denaturation due to the complexation with the SWNTs.

Proc. of SPIE Vol. 7118 71180M-2

C C C

I

00 — OD

C

000

fH C

0Q H

C C

EIIiptidty [mdeg]

Figure 1. CD spectra of DNA-SWNT-CTMA (method 1 and method 2)

3.2 Absorption spectroscopy The Absorption spectra taken on DNA-SWCNT-CTMA blends (method 1 and method 2) in the UV-NIR wavelength range show absorption peaks related to the carbon nanotubes. See fig. 2. The presence, as well as the increase of the absorption peaks in DNA-SWNT-CTMA method 1are attributed to an enhanced dispersion of SWNTs when blended with DNA first.18

DNA-SVTONT-OTMA (01)

400

fl

800 1200 1600 %V avel en gUi (mnn)

2000

Figure 2. UV-NIR absorption spectra of DNA-SWCNT-CTMA (method 1 and method 2)


4. DNA FIELD EFFECT TRANSISTORS (BioFETs) 4.1 Design and fabrication In this study, the structure of DNA-based OFET is similar to that of a traditional silicon metal-oxide semiconductor field effect transistor (MOSFET) with bottom gate and bottom contact configuration (Fig. 3). The heavily doped silicon substrate at the bottom serves a dual function as both the gate electrode and mechanical support. A 300nm thick SiO2 is thermally grown on the Si surface and serves as gate insulator on which Cr/Au electrodes are sputtered. DNA-based material Cr/Au electrodes

2. 3. 4. 5. 6.

300 nm SiO2

Heavily doped Si

Figure 3. DNA-based OFET structure: bottom gate, bottom contact

Because of the limitation in our patterning resolution, the shortest channel length that was achieved was around 1mm and the channel width was around 4mm. Thin (0.5µm - 1µm thick) DNA-SWCNT-CTMA films were spin deposited on top of the source and drain electrodes. A Keithly 4200 parametric analyzer was used to characterize the BioFET devices. In our study, field-effect mobility and threshold voltages were calculated in the saturation regime from the saturation region current equation of the standard MOSFET, using the highest slope of the square root of the drain-source current to the gate-source voltage or IDS1/2 vs VGS plot. The current equation of an FET in saturation is:

ID = fLsaH

H

Ij•GS —

2

where µsat is the field effect mobility, Ci is the capacitance per unit area of the gate dielectric, Vt the threshold voltage, and W (width) and L (length) are the dimensions of the semiconductor channel defined by the source and drain electrodes of the FET.

4.2 Characterization The drain-source current (IDS) and drain-source voltage (VDS) characteristics were determined with applied drainsource voltages ranging from 0 to 20 V with gate biases varying from -10 to 10 V. The test results plotted in Figs. 4 and 5 show a deviation in the IDS-VDS relationships from the expected ideal case. The BioFETs studied here exhibited a high source-drain current when no gate voltage was applied. Y. Xu et al.19 attributed this behavior to charged impurities possibly present in the semiconducting material.


Drain-source current I DS (µA)

30

Vgs = 0V 25

Vgs = 5V Vgs = 10V

20 15 10 5 0 0

5

10

15

20

Drain-source voltage VDS (V) Figure 4. Output characteristics of OFET using DNA-SWCNT-CTMA (obtained be method 1) as a semiconducting layer

16

D ra in - s o u rc e c u rre n t I

DS

(µ A )

Vga = -10V Vgs = -5V Vgs = 0V Vgs = 5V Vgs = 10V

12

8

4

0 0

5

10

15

20

Drain-source voltage V DS (V) Fig.5. Output characteristics of OFET using DNA-SWCNT-CTMA (obtained by method 2) as a semiconductor layer

It is clear that the gate-source voltage (VGS) modulation of the drain-source current (IDS) is low, seen from the output characteristics of the devices made using DNA-SWCNT-CTMA as shown in figs.


4 (method 1) and 5 (method 2). This may be due to reaglomeration of some of the nanotubes into bundles. Therefore, a technique for aligning the SWNTs is the key. Comparing method 1 and method 2, we found that, even though small, the gate modulation using method 1 (where SWNTs were blended with DNA first) was larger than using method 2 (where SWNTs were blended with CTMA first). The lower gate modulation observed in method 2 is most likely due to the low dispersion efficiency of the nanotubes when blended with CTMA first. See Fig. 2. A significant offset voltage is also seen in the output characteristics of these devices. S. P Tiwari reported an offset voltage on their Pentacene-based OFETs and attributed such behavior to a high contact resistance due primarily to the interface polymer/electrode effects and channel dimensions L/W.22 Our FET designs for this study had a W/L ratio less than 10, which made the contribution of the contact resistance considerable in comparison to the channel resistance most likely causing the offset in the drain voltages. In addition a better matched, more ideal gate dielectric is also crucial. Effective free charge carrier mobilities values were too difficult to extract form the data. Further characterization of these devices is currently underway.

CONCLUSION Complexes of DNA and SWNTs show promise as organic-based semiconductor materials. These low cost bioorganic materials have been used in thin film organic transistors and have exhibited field effect mobilities, however, are still currently low in comparison to the commercially available organic semiconductors. Improvement in the “doping” process and better suited gate dielectric will lead to better control of the electrical properties. Studies are also currently being conducted on the effects of geometry and the electrode/polymer interface on device characteristics.

ACKOWLEDGEMENTS The authors wish to thank Professor Naoya Ogata, Chitose Institute of Science and Technology, for providing the source of DNA for this investigation and the US Air Force research Laboratory, Materials and Manufacturing Directorate, the US Air Force Office of Scientific Research and the Defense Advanced Research Projects Agency, Microsystems Technology Office for their financial support. We also acknowledge the technical assistance of Gerry Landis of the University of Dayton Research Institute.

REFERENCES [1] [2] [3] [4] [5] [6] [7] [8]

Okahata Y., Kobayashi T., Tanaka K., and Shimomura M., ”Metallic Conduction through Engineered DNA: DNA Nanoelectronic Building Blocks”, J. Am. Chem. Soc., 120, 6165, (1998) Fink H. W., and Schonenberger C. “Electrical conduction through DNA molecules” Nature London, 398, 407, (1999) Kelly S. O., Jackson N. M., Hill M. G., and Barton J. K.,”Long-Range Electron Transfer through DNA Films” Angew. Chem. Int. Ed. Engl., 38, 941, (1998) A. Yu. Kasumov, D. V. Klinov, P.-E. Roche, S. Gue´ ron, and H. Bouchiat, “Thickness and low-temperature conductivity of DNA molecules”, Appl. Phys. Lett., 84(6), 1007-1009, (2004) A. Dodabalapur, Z. Bao, A. Makhija, J.G. Laquidanum, V.R. Raju, Y. Feng, H.E. Katz, and J. Rogers “Organic smart pixels”, Appl. Phys. Lett., 73, 142, (1998) Jackson Th. N., Lin Y-Y., Gundlach D.J. and Klauk H., IEEE J. of selected Topics in Quantum Electronics, 4, 101, (1998) Ma E.Y., Theiss S.D., Lu M.H., Wu C. C., Sturm J.C. and S. Wagner, IEDM Technical Digest, 535, (1995) D.M. de Leeuw, Blom P.W.M., Hart C.M., Mutsaers C.M.J., Dury C.J., Matters M. and Termeer H., IEDM Technical Digest, 331, (1997)


[9] [10] [11] [12]

[13] [14] [15] [16] [17] [18] [19] [20]

Lin Y.-Y., Dodabalapur A., Sarpeshkar R., Bao Z., Baldwin W. Li, K., Raju V.R. and Katz H.E., “Organic complementary ring oscillators”, Appl. Phys. Lett., 74, 2714, (1999) Drury C.J., Mutsaers C.M.J. and de Leeuw D.M. “Low-cost all-polymer integrated circuits”, Appl. Phys. Lett., 73, 108, (1998) Klauk H., Gundlach D.J. and Jackson Th. N., IEEE Electr. Dev. Lett., 20, 289, (1999) Wang L., Yoshida J., Ogata N., Sasaki S. and Kajiyama T. “Self-assembled supramolecular films derived from marine deoxyribonucleic acid (DNA)-cationic surfactant complexes: Large-scale preparation and optical and thermal properties”, Chem. Mater., 13(4), 1273–1281, (2001) Yaney P. P., Heckman E. M., Grote J. G., "Resistivity and electric-field poling behaviors of DNA-based polymers compared to selected non-DNA polymers” , SPIE Proc., 6646, 61170J–6, (2006) Singh B., Sariciftci N. S., Grote J. G. and Hopkins F. K., “Bio-organic-semiconductor-field-effect-transistor based on deoxyribonucleic acid gate dielectric”, J. Appl. Phys., 100(2), 024514–4, (2006) Hagen J. A., Li W., Steckl A. J. and Grote J. G. “Enhanced emission efficiency in organic light-emitting diodes using deoxyribonucleic acid complex as an electron blocking layer”, Appl. Phys. Lett., 88(17), 171109, (2006) Ouchen F., Kim S., Hay M., Zate H., Subramanyam S., Grote J., Bartsch C. and Naik R., “DNA-conductive polymer blends for applications in Biopolymer based field effect transistors (FETs)”, SPIE Proc., 7040, (2008) J. Liu, A.G. Rinzler, H. Dai, J.H. Hafner, R.K., “Fullerene Pipes”, 280(5367), 1253 - 1256 S.N Kim, K.M. Singh, F. Ouchen, J.G. Grote, R.R. Naik, NSTI-Nanotech, 1, 132-135, (2008) Y. Xu and P. R. Berger, J. Appl. Phys., 95(3), 1501, (2004). S.P. Tiwari, V. R. Rao, H. S. Tan, E.B. Namdas, S. G. Mhaisalkar, IEEE Electr. Dev. Lett., 20, 289, (2007).
