Organic semiconductors have been the subject of active research for over a decade now, with applications emerging in light-emitting displays and printable electronic circuits. One characteristic feature of these materials is the strong trapping of electrons but not holes1: organic field-effect transistors (FETs) typically show p-type, but not n-type, conduction even with the appropriate low-work-function electrodes, except for a few special high-electron-affinity2,3,4 or low-bandgap5 organic semiconductors. Here we demonstrate that the use of an appropriate hydroxyl-free gate dielectric—such as a divinyltetramethylsiloxane-bis(benzocyclobutene) derivative (BCB; ref. 6)—can yield n-channel FET conduction in most conjugated polymers. The FET electron mobilities thus obtained reveal that electrons are considerably more mobile in these materials than previously thought. Electron mobilities of the order of 10-3 to 10-2 cm2 V-1 s-1 have been measured in a number of polyfluorene copolymers and in a dialkyl-substituted poly(p-phenylenevinylene), all in the unaligned state. We further show that the reason why n-type behaviour has previously been so elusive is the trapping of electrons at the semiconductor–dielectric interface by hydroxyl groups, present in the form of silanols in the case of the commonly used SiO2 dielectric. These findings should therefore open up new opportunities for organic complementary metal-oxide semiconductor (CMOS) circuits, in which both p-type and n-type behaviours are harnessed.
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Dimitrakopoulos, C. D. & Malenfant, P. R. L. Organic thin film transistors for large area electronics. Adv. Mater. 14, 99–117 (2002)
Dodabalapur, A., Katz, H. E., Torsi, L. & Haddon, R. C. Organic heterostructure field-effect transistors. Science 269, 1560–1562 (1995)
Katz, H. E. et al. A soluble and air-stable organic semiconductor with high electron mobility. Nature 404, 478–481 (2000)
Babel, A. & Jenekhe, S. A. High electron mobility in ladder polymer field-effect transistors. J. Am. Chem. Soc. 125, 13656–13657 (2003)
Meijer, E. J. et al. Solution-processed ambipolar organic field-effect transistors and inverters. Nature Mater. 2, 678–682 (2003)
Chua, L. L., Ho, P. K. H., Sirringhaus, H. & Friend, R. H. High stability ultrathin spin-on benzocyclobutene gate dielectric for polymer field-effect transistors. Appl. Phys. Lett. 84, 3400–3402 (2004)
Veres, J., Ogier, S. D., Leeming, S. W., Cupertino, D. C. & Khaffaf, S. M. Low-k insulators as the choice of dielectrics in organic field-effect transistors. Adv. Funct. Mater. 13, 199–204 (2003)
Chua, L. L., Ho, P. K. H., Sirringhaus, H. & Friend, R. H. Observation of field-effect behaviour at self-organised interfaces. Adv. Mater. 16, 1609–1615 (2004)
Brown, A. R., De Leeuw, D. M., Lous, E. J. & Havinga, E. E. Organic n-type field-effect transistors. Synth. Met. 66, 257–261 (1994)
Sirringhaus, H. et al. Mobility enhancement in conjugated polymer field-effect transistors through chain alignment in a liquid-crystalline phase. Appl. Phys. Lett. 77, 406–408 (2000)
Kim, J. S., Ho, P. K. H., Greenham, N. C. & Friend, R. H. Electroluminescence emission pattern of organic light-emitting diodes: Implications for device efficiency calculations. J. Appl. Phys. 88, 1073–1081 (2000)
Bozano, L., Carter, S., Scott, J., Malliaras, G. & Brock, P. Temperature- and field-dependent electron and hole mobilities in polymer light-emitting diodes. Appl. Phys. Lett. 74, 1132–1134 (1999)
Ho, P. K. H. et al. Molecular-scale interface engineering for polymer light-emitting diodes. Nature 404, 481–484 (2000)
Nagasawa, Y. et al. The study of the thermal oxide films on silicon wafers by Fourier transform infrared attenuated total reflection spectroscopy. J. Appl. Phys. 68, 1429–1434 (1990)
Dugas, V. & Chevalier, Y. Surface hydroxylation and silane grafting on fumed and thermal silica. J. Colloid Interf. Sci. 264, 354–361 (2003)
Perry, C. C. & Li, X. Structural studies of gel phases. J. Chem. Soc. Faraday Trans. 87, 3857–3862 (1991)
Tardif, F., Chabli, A., Kanel, A., Rochat, N. & Veillerot, M. Thermal evolution of chemical oxides and (100) silicon at 300 °C in ambient air as seen by attenuated total reflection infrared spectroscopy. J. Electrochem. Soc. 150, G333–G338 (2003)
Nicollian, E. H., Berglund, C. N., Schmidt, P. F. & Andrews, J. M. Electrochemical charging of thermal SiO2 films by injected electron currents. J. Appl. Phys. 42, 5654–5664 (1971)
Hartstein, A. & Young, D. R. Identification of electron traps in thermal silicon dioxide films. Appl. Phys. Lett. 38, 631–633 (1981)
Malenfant, P. R. L. et al. N-type organic thin-film transistor with high field-effect mobility based on a N-N′-dialkyl-3,4,9,10-perylene tetracarboxylic diimide derivative. Appl. Phys. Lett. 80, 2517–2519 (2002)
Salleo, A., Chabinyc, M. L., Yang, M. S. & Street, R. A. Polymer thin-film transistors with chemically modified dielectric interfaces. Appl. Phys. Lett. 81, 4383–4385 (2002)
Angst, D. L. & Simmons, G. W. Moisture absorption characteristics of organosiloxane self-assembled monolayers. Langmuir 7, 2236–2242 (1991)
Wasserman, S. R., Tao, Y. T. & Whitesides, G. M. Structure and reactivity of alkylsiloxane monolayers formed by reaction of alkyltrichlorosilanes on silicon substrates. Langmuir 5, 1074–1087 (1989)
Sirringhaus, H. et al. Two-dimensional charge transport in self-organised, high-mobility conjugated polymers. Nature 401, 685–688 (1999)
Wilson, R. J. Polymer Field-effect Transistors from Polyfluorene-based Conjugated Polymers. PhD thesis, Univ. Cambridge (2002)
We thank A. Achen for providing the BCB material, which is commercially available as Dow Cyclotene, and Merck KGaA for P3HT. L-L.C. and J-F.C. thank the EPSRC Carbon-Based Electronics programme for support, and J.Z. thanks the Gates Cambridge Trust for support. P.K-H.H. thanks St John's College for a research fellowship, the National University of Singapore for research support, and S. J. Chua for technical discussions, support and access to laboratory facilities. We also thank C.-C. Chum for technical support.
H.S. and R.H.F. are directors of Plastic Logic Ltd, a University of Cambridge start-up company with activities within this broad field.
Supplementary Figure S1 provides further examples of polymer gate dielectrics that have also yielded n-channel FETs. Supplementary Figure S2 provides evidence that long chain self-assembled monolayers slow down occupation but do not completely passivate the electron traps at the SiO2 interface. Supplementary Figure S3 provides further evidence for electron-trapping from the gate-threshold shifts in p-type FETs after positive gate biasing. (PDF 187 kb)
This section discusses the differing time scales for trapping of electrons, which is probed by decay of the electron field-effect current, and for advancement of the electrochemical reaction front across the channel length, which is probed by the ATR-FTIR experiment. (PDF 78 kb)
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Chua, LL., Zaumseil, J., Chang, JF. et al. General observation of n-type field-effect behaviour in organic semiconductors. Nature 434, 194–199 (2005). https://doi.org/10.1038/nature03376
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