Simultaneous Modification of Bottom‐Contact Electrode and Dielectric Surfaces for Organic Thin‐Film Transistors Through Single‐Component Spin‐Cast Monolayers

An efficient process is developed by spin-coating a single-component, self-assembled monolayer (SAM) to simultaneously modify the bottom-contact electrode and dielectric surfaces of organic thin-film transistors (OTFTs). This efficient interface modification is achieved using n-alkyl phosphonic acid based SAMs to prime silver bottom-contacts and hafnium oxide (HfO{sub 2}) dielectrics in low-voltage OTFTs. Surface characterization using near edge X-ray absorption fine structure (NEXAFS) spectroscopy, X-ray photoelectron spectroscopy (XPS), attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, atomic force microscopy (AFM), and spectroscopic ellipsometry suggest this process yields structurally well-defined phosphonate SAMs on both metal and oxide surfaces. Rational selection of the alkyl length of the SAM leads to greatly enhanced performance for both n-channel (C60) and p-channel (pentacene) based OTFTs. Specifically, SAMs of n-octylphos-phonic acid (OPA) provide both low-contact resistance at the bottom-contact electrodes and excellent interfacial properties for compact semiconductor grain growth with high carrier mobilities. OTFTs based on OPA modifi ed silver electrode/HfO{sub 2} dielectric bottom-contact structures can be operated using < 3V with low contact resistance (down to 700 Ohm-cm), low subthreshold swing (as low as 75 mV dec{sup -1}), high on/off current ratios of 107, and charge carrier mobilities as high as 4.6 and 0.8 cm{sup 2} V{supmore » -1} s{sup -1}, for C60 and pentacene, respectively. These results demonstrate that this is a simple and efficient process for improving the performance of bottom-contact OTFTs.« less

[1]  W. A. Dench,et al.  Quantitative electron spectroscopy of surfaces: A standard data base for electron inelastic mean free paths in solids , 1979 .

[2]  J. Fréchet,et al.  Organic semiconducting oligomers for use in thin film transistors. , 2007, Chemical reviews.

[3]  H. Klauk,et al.  Ultralow-power organic complementary circuits , 2007, Nature.

[4]  S. Iannotta,et al.  Pentacene Thin Film Growth , 2004 .

[5]  L. R. Robinson,et al.  Formation of an organized monolayer by solution adsorption of octadecyltrichlorosilane on gold: electrochemical properties and structural characterization , 1986 .

[6]  A. Jen,et al.  Low-voltage organic thin-film transistors with π-σ-phosphonic acid molecular dielectric monolayers , 2008 .

[7]  George M. Whitesides,et al.  Structure and reactivity of alkylsiloxane monolayers formed by reaction of alkyltrichlorosilanes on silicon substrates , 1989 .

[8]  F. Schreiber.  Structure and growth of self-assembling monolayers , 2000 .

[9]  Zhenan Bao,et al.  The Role of OTS Density on Pentacene and C60 Nucleation, Thin Film Growth, and Transistor Performance , 2009 .

[10]  Jean-Paul Kleider,et al.  Electrical Properties of Amorphous Silicon Transistors and MIS‐Devices: Comparative Study of Top Nitride and Bottom Nitride Configurations , 1993 .

[11]  Stephen R. Forrest,et al.  Very-high-efficiency double-heterostructure copper phthalocyanine/C60 photovoltaic cells , 2001 .

[12]  P. Batson,et al.  Carbon 1s near-edge-absorption fine structure in graphite. , 1993, Physical review. B, Condensed matter.

[13]  Tobin J. Marks,et al.  High-mobility bottom-contact n-channel organic transistors and their use in complementary ring oscillators , 2006 .

[14]  George M. Whitesides,et al.  Comparison of the Structures and Wetting Properties of Self-Assembled Monolayers of n- Alkanethiols on the Coinage Metal Surfaces, Cu, Ag, Au' , 1991 .

[15]  Stephen R. Forrest,et al.  The path to ubiquitous and low-cost organic electronic appliances on plastic , 2004, Nature.

[16]  Paul H. Wöbkenberg,et al.  Low-voltage organic transistors based on solution processed semiconductors and self-assembled monolayer gate dielectrics , 2008 .

[17]  J. Randon,et al.  Modification of ceramic membrane surfaces using phosphoric acid and alkyl phosphonic acids and its effects on ultrafiltration of BSA protein , 1995 .

[18]  Sampath Purushothaman,et al.  High-performance bottom electrode organic thin-film transistors , 2001 .

[19]  J. Stöhr,et al.  The orientation of Langmuir–Blodgett monolayers using NEXAFS , 1988 .

[20]  C. Frisbie,et al.  Systems for orthogonal self-assembly of electroactive monolayers on Au and ITO: an approach to molecular electronics , 1995 .

[21]  Barbara Stadlober,et al.  Orders‐of‐Magnitude Reduction of the Contact Resistance in Short‐Channel Hot Embossed Organic Thin Film Transistors by Oxidative Treatment of Au‐Electrodes , 2007 .

[22]  P. Feulner,et al.  Direct probing molecular twist and tilt in aromatic self-assembled monolayers. , 2007, Journal of the American Chemical Society.

[23]  I. Hill,et al.  Influence of self-assembled monolayer chain length on modified gate dielectric pentacene thin-film transistors , 2009 .

[24]  Y. Arakawa,et al.  Bottom-contact fullerene C60 thin-film transistors with high field-effect mobilities , 2008 .

[25]  Gilles Horowitz,et al.  Theory of the organic field-effect transistor , 1999 .

[26]  I. Hertel,et al.  Growth mechanisms of C60-molecular beam epitaxy on mica , 1993 .

[27]  S. Mannsfeld,et al.  Controlled Deposition of Crystalline Organic Semiconductors for Field‐Effect‐Transistor Applications , 2009 .

[28]  S. Bernasek,et al.  Characterization of self-assembled organic films using differential charging in X-ray photoelectron spectroscopy. , 2006, Langmuir : the ACS journal of surfaces and colloids.

[29]  Yu Wu,et al.  Single‐Layer Pentacene Field‐Effect Transistors Using Electrodes Modified With Self‐assembled Monolayers , 2009 .

[30]  A. Ulman,et al.  Formation and Structure of Self-Assembled Monolayers. , 1996, Chemical reviews.

[31]  Chan Eon Park,et al.  The Effect of Gate‐Dielectric Surface Energy on Pentacene Morphology and Organic Field‐Effect Transistor Characteristics , 2005 .

[32]  A. Jen,et al.  Dielectric surface-controlled low-voltage organic transistors via n-alkyl phosphonic acid self-assembled monolayers on high-k metal oxide. , 2010, ACS applied materials & interfaces.

[33]  P. Mutin,et al.  Hybrid materials from organophosphorus coupling molecules , 2005 .

[34]  G. Hähner,et al.  Order and Orientation in Self-Assembled Long Chain Alkanephosphate Monolayers Adsorbed on Metal Oxide Surfaces , 2001 .

[35]  A. Fadeev,et al.  Thermal stability of organic monolayers chemically grafted to minerals. , 2005, Journal of colloid and interface science.

[36]  A. Morpurgo,et al.  Tunable Fröhlich polarons in organic single-crystal transistors , 2006, Nature materials.

[37]  B. de Boer,et al.  Tuning of Metal Work Functions with Self‐Assembled Monolayers , 2005 .

[38]  T. Jackson,et al.  Pentacene TFT with improved linear region characteristics using chemically modified source and drain electrodes , 2001, IEEE Electron Device Letters.

[39]  N. McIntyre,et al.  Delivering octadecylphosphonic acid self-assembled monolayers on a Si wafer and other oxide surfaces. , 2006, The journal of physical chemistry. B.

[40]  A. Arias,et al.  Materials and applications for large area electronics: solution-based approaches. , 2010, Chemical reviews.

[41]  T. Weidner,et al.  Balance of structure-building forces in selenium-based self-assembled monolayers. , 2007, Journal of the American Chemical Society.

[42]  S. Tosatti,et al.  ORIENTATION IN METHYL- AND HYDROXYL-TERMINATED SELF-ASSEMBLED ALKANEPHOSPHATE MONOLAYERS ON TITANIUM OXIDE SURFACES INVESTIGATED WITH SOFT X-RAY ABSORPTION , 2002 .

[43]  B. Bhushan,et al.  Alkylphosphonate modified aluminum oxide surfaces. , 2006, The journal of physical chemistry. B.

[44]  D. Hobara,et al.  Chain-length-dependent change in the structure of self-assembled monolayers of n-alkanethiols on Au(111) probed by broad-bandwidth sum frequency generation spectroscopy , 2003 .

[45]  Michael S. Shur,et al.  An experimental study of contact effects in organic thin film transistors , 2006 .

[46]  P. Mutin,et al.  Anchoring of Phosphonate and Phosphinate Coupling Molecules on Titania Particles , 2001 .

[47]  Yasuhiko Arakawa,et al.  Pentacene-based organic field-effect transistors , 2008 .

[48]  A. Fadeev,et al.  Hydrolytic stability of organic monolayers supported on TiO2 and ZrO2. , 2004, Langmuir : the ACS journal of surfaces and colloids.

[49]  D. Allara,et al.  Spontaneously organized molecular assemblies. 4. Structural characterization of n-alkyl thiol monolayers on gold by optical ellipsometry, infrared spectroscopy, and electrochemistry , 1987 .

[50]  John E. Anthony,et al.  Contact-induced crystallinity for high-performance soluble acene-based transistors and circuits. , 2008, Nature materials.

[51]  C. Nuckolls,et al.  Chemical complementarity in the contacts for nanoscale organic field-effect transistors. , 2006, Journal of the American Chemical Society.

[52]  Eugenio Cantatore,et al.  Bottom-up organic integrated circuits , 2008, Nature.

[53]  J. Park,et al.  Energy level alignment and two-dimensional structure of pentacene on Au(111) surfaces , 2002 .

[54]  Hylke B. Akkerman,et al.  Towards molecular electronics with large-area molecular junctions , 2006, Nature.

[55]  B. Meredig,et al.  Ordering of poly(3-hexylthiophene) nanocrystallites on the basis of substrate surface energy. , 2009, ACS nano.

[56]  Y. Nishi,et al.  Solution-processed flexible organic transistors showing very-low subthreshold slope with a bilayer polymeric dielectric on plastic , 2009 .

[57]  T. Weidner,et al.  Effect of the Bending Potential on Molecular Arrangement in Alkaneselenolate Self-Assembled Monolayers , 2008 .

[58]  Richard H. Friend,et al.  General observation of n-type field-effect behaviour in organic semiconductors , 2005, Nature.

[59]  P. Annibale,et al.  Charge injection across self-assembly monolayers in organic field-effect transistors: odd-even effects. , 2007, Journal of the American Chemical Society.

[60]  I. Hill,et al.  Improved organic thin-film transistor performance using novel self-assembled monolayers , 2006 .

[61]  Tae-Wook Kim,et al.  Influence of metal-molecule contacts on decay coefficients and specific contact resistances in molecular junctions , 2007 .

[62]  C. Wöll,et al.  RYDBERG TRANSITIONS IN X-RAY ABSORPTION SPECTROSCOPY OF ALKANES : THE IMPORTANCE OF MATRIX EFFECTS , 1999 .

[63]  G M Whitesides,et al.  Orthogonal Self-Assembled Monolayers: Alkanethiols on Gold and Alkane Carboxylic Acids on Alumina , 1989, Science.

[64]  Do Hwan Kim,et al.  Effect of the phase states of self-assembled monolayers on pentacene growth and thin-film transistor characteristics. , 2008, Journal of the American Chemical Society.

[65]  Yutaka Ito,et al.  Crystalline ultrasmooth self-assembled monolayers of alkylsilanes for organic field-effect transistors. , 2009, Journal of the American Chemical Society.

[66]  Bernard Kippelen,et al.  High-performance and electrically stable C60 organic field-effect transistors , 2007 .

[67]  N. Koch,et al.  Bonding self-assembled, compact organophosphonate monolayers to the native oxide surface of silicon. , 2003, Journal of the American Chemical Society.

[68]  Ralph G. Nuzzo,et al.  Spontaneously organized molecular assemblies. 1. Formation, dynamics, and physical properties of n-alkanoic acids adsorbed from solution on an oxidized aluminum surface , 1985 .

[69]  John E. Anthony,et al.  High mobility solution processed 6,13-bis(triisopropyl-silylethynyl) pentacene organic thin film transistors , 2007 .

[70]  N. S. Sariciftci,et al.  Correlation of crystalline and structural properties of C60 thin films grown at various temperature with charge carrier mobility , 2007 .

[71]  D. Burdinski,et al.  Universal ink for microcontact printing. , 2006, Angewandte Chemie.

[72]  Hong Ma,et al.  Study on the formation of self-assembled monolayers on sol-gel processed hafnium oxide as dielectric layers. , 2009, Langmuir : the ACS journal of surfaces and colloids.

[73]  Stefan Possanner,et al.  Threshold Voltage Shifts in Organic Thin‐Film Transistors Due to Self‐Assembled Monolayers at the Dielectric Surface , 2009 .

[74]  E. Umbach,et al.  Analysis of the x-ray absorption spectra of linear saturated hydrocarbons using the Xα scattered-wave method , 1998 .

[75]  D. Allara,et al.  Physical and Electronic Structure Effects of Embedded Dipoles in Self-Assembled Monolayers: Characterization of Mid-Chain Ester Functionalized Alkanethiols on Au{111} , 2008 .

[76]  D. A. Corley,et al.  Controlling charge injection in organic field-effect transistors using self-assembled monolayers. , 2006, Nano letters.

[77]  Bernard Kippelen,et al.  High-performance C60 n-channel organic field-effect transistors through optimization of interfaces , 2008 .

[78]  M. Ratner,et al.  Molecular Self‐Assembled Monolayers and Multilayers for Organic and Unconventional Inorganic Thin‐Film Transistor Applications , 2009 .

[79]  Tobin J. Marks,et al.  σ-π molecular dielectric multilayers for low-voltage organic thin-film transistors , 2005 .

[80]  K. Seki,et al.  ENERGY LEVEL ALIGNMENT AND INTERFACIAL ELECTRONIC STRUCTURES AT ORGANIC/METAL AND ORGANIC/ORGANIC INTERFACES , 1999 .

[81]  Ute Zschieschang,et al.  Low-voltage organic thin-film transistors with large transconductance , 2007 .

[82]  Alex K.-Y. Jen,et al.  Interface Engineering for Organic Electronics , 2010, Advanced Functional Materials.

[83]  Takao Someya,et al.  Effects of the alkyl chain length in phosphonic acid self-assembled monolayer gate dielectrics on the performance and stability of low-voltage organic thin-film transistors , 2009 .

[84]  Y. Arakawa,et al.  Threshold voltage control of bottom-contact n-channel organic thin-film transistors using modified drain/source electrodes , 2009 .

[85]  Hong Ma,et al.  π‐σ‐Phosphonic Acid Organic Monolayer/Sol–Gel Hafnium Oxide Hybrid Dielectrics for Low‐Voltage Organic Transistors , 2008 .

[86]  Y. Tao,et al.  Molecular orientation of evaporated pentacene films on gold: alignment effect of self-assembled monolayer. , 2005, Langmuir : the ACS journal of surfaces and colloids.

[87]  Neal R. Armstrong,et al.  Phosphonic Acid Modification of Indium−Tin Oxide Electrodes: Combined XPS/UPS/Contact Angle Studies† , 2008 .

[88]  G. Whitesides,et al.  Self-Assembled Monolayers of Long-Chain Hydroxamic Acids on the Native Oxides of Metals , 1995 .

[89]  S. Bernasek,et al.  Monolayer vs. multilayer self-assembled alkylphosphonate films: X-ray photoelectron spectroscopy studies , 2006 .

[90]  Michael Thomas Dugger,et al.  Mechanistic Aspects of Alkylchlorosilane Coupling Reactions , 1997 .

[91]  A. Jen,et al.  π-σ-Phosphonic acid organic monolayer–amorphous sol–gel hafnium oxide hybrid dielectric for low-voltage organic transistors on plastic , 2009 .

[92]  Thomas N. Jackson,et al.  Contact resistance extraction in pentacene thin film transistors , 2003 .

[93]  G. Poirier,et al.  Characterization of Organosulfur Molecular Monolayers on Au(111) using Scanning Tunneling Microscopy. , 1997, Chemical reviews.

[94]  T. Shimoda,et al.  Control of carrier density by self-assembled monolayers in organic field-effect transistors , 2004, Nature materials.

[95]  C. Gerber,et al.  Real-Space Observation of Nanoscale Molecular Domains in Self-Assembled Monolayers , 1994 .

[96]  Ralph G. Nuzzo,et al.  Fundamental studies of microscopic wetting on organic surfaces. 1. Formation and structural characterization of a self-consistent series of polyfunctional organic monolayers , 1990 .

[97]  John E Anthony,et al.  Functionalized acenes and heteroacenes for organic electronics. , 2006, Chemical reviews.