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Field-effect Transistors (field-effect + transistor)
Kinds of Field-effect Transistors Selected AbstractsIntegration of a Rib Waveguide Distributed Feedback Structure into a Light-Emitting Polymer Field-Effect TransistorADVANCED FUNCTIONAL MATERIALS, Issue 11 2009Michael C. Gwinner No abstract is available for this article. [source] Non-volatile Ferroelectric Poly(vinylidene fluoride- co -trifluoroethylene) Memory Based on a Single-Crystalline Tri-isopropylsilylethynyl Pentacene Field-Effect TransistorADVANCED FUNCTIONAL MATERIALS, Issue 10 2009Seok Ju Kang Abstract A new type of nonvolatile ferroelectric poly(vinylidene fluoride- co -trifluoroethylene) (P(VDF-TrFE)) memory based on an organic thin-film transistor (OTFT) with a single crystal of tri-isopropylsilylethynyl pentacene (TIPS-PEN) as the active layer is developed. A bottom-gate OTFT is fabricated with a thin P(VDF-TrFE) film gate insulator on which a one-dimensional ribbon-type TIPS-PEN single crystal, grown via a solvent-exchange method, is positioned between the Au source and drain electrodes. Post-thermal treatment optimizes the interface between the flat, single-crystalline ab plane of TIPS-PEN and the polycrystalline P(VDF-TrFE) surface with characteristic needle-like crystalline lamellae. As a consequence, the memory device exhibits a substantially stable source,drain current modulation with an ON/OFF ratio hysteresis greater than 103, which is superior to a ferroelectric P(VDF-TrFE) OTFT that has a vacuum-evaporated pentacene layer. Data retention longer than 5,×,104 s is additionally achieved in ambient conditions by incorporating an interlayer between the gate electrode and P(VDF-TrFE) thin film. The device is environmentally stable for more than 40 days without additional passivation. The deposition of a seed solution of TIPS-PEN on the chemically micropatterned surface allows fabrication arrays of TIPS-PEN single crystals that can be potentially useful for integrated arrays of ferroelectric polymeric TFT memory. [source] Integration of a Rib Waveguide Distributed Feedback Structure into a Light-Emitting Polymer Field-Effect TransistorADVANCED FUNCTIONAL MATERIALS, Issue 9 2009Michael C. Gwinner Abstract Ambipolar light-emitting organic field-effect transistors (LEFETs) possess the ability to efficiently emit light due to charge recombination in the channel. Since the emission can be made to occur far from the metal electrodes, the LEFET structure has been proposed as a potential architecture for electrically pumped organic lasers. Here, a rib waveguide distributed feedback structure consisting of tantalum pentoxide (Ta2O5) integrated within the channel of a top gate/bottom contact LEFET based on poly(9,9-dioctylfluorene- alt -benzothiadiazole) (F8BT) is demonstrated. The emitted light is coupled efficiently into the resonant mode of the DFB waveguide when the recombination zone of the LEFET is placed directly above the waveguide ridge. This architecture provides strong mode confinement in two dimensions. Mode simulations are used to optimize the dielectric thickness and gate electrode material. It is shown that electrode absorption losses within the device can be eliminated and that the lasing threshold for optical pumping of the LEFET structure with all electrodes (4.5,µJ cm,2) is as low as that of reference devices without electrodes. These results enable quantitative judgement of the prospects for realizing an electrically pumped organic laser based on ambipolar LEFETs. The proposed device provides a powerful, low-loss architecture for integrating high-performance ambipolar organic semiconductor materials into electrically pumped lasing structures. [source] A Water-Gate Organic Field-Effect TransistorADVANCED MATERIALS, Issue 23 2010Loig Kergoat High-dielectric-constant insulators, organic monolayers, and electrolytes have been successfully used to generate organic field-effect transistors operating at low voltages. Here, we report on a device gated with pure water. By replacing the gate dielectric by a simple water droplet, we produce a transistor that entirely operates in the field-effect mode of operation at voltages lower than 1,V. This result creates opportunities for sensor applications using water-gated devices as transducing medium. [source] High-Performance Field-Effect Transistor Based on Dibenzo[d,d,]thieno[3,2- b;4,5- b,]dithiophene, an Easily Synthesized Semiconductor with High Ionization Potential,ADVANCED MATERIALS, Issue 19 2007H. Gao Three simple, controlled steps are all it takes to synthesize the title pentacene analogue DBTDT (see figure). The material's high ionization potential, high thermal and photostability, high mobilities, and an on/off ratio larger than 106 at a substrate temperature of ca.,36,°C, as reported here, suggest that DBTDT will be extremely valuable for applications in plastic organic electronics. [source] ZnO Nanofiber Field-Effect Transistor Assembled by ElectrospinningJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2008Hui Wu A ZnO nanofiber field-effect transistor (FET) was assembled by electrospinning. Uniform ZnO nanofibers with a diameter of ,70 nm and length over 100 ,m were first synthesized by electrospinning. Using two paralleled electrodes as fiber collectors, we have successfully placed a single ZnO nanofiber on the electrodes, and an FET device was fabricated based on the assembled nanofiber. An electrical transport measurement was conducted on the FET device, showing that ZnO nanofibers are intrinsic n- type semiconductors. The present findings demonstrate that electrospinning can potentially be used as a straightforward and cost-effective means for the assembly of one-dimensional nanostuctures for building integrated nanodevices for various applications, such as transistors, sensors, diodes, and photodetectors. [source] Analysis of Dopamine and Tyrosinase Activity on Ion-Sensitive Field-Effect Transistor (ISFET) DevicesCHEMISTRY - A EUROPEAN JOURNAL, Issue 26 2007Ronit Freeman Abstract Dopamine (1) and tyrosinase (TR) activities were analyzed by using chemically modified ion-sensitive field-effect transistor (ISFET) devices. In one configuration, a phenylboronic acid functionalized ISFET was used to analyze 1 or TR. The formation of the boronate,1 complex on the surface of the gate altered the electrical potential associated with the gate, and thus enabled 1 to be analyzed with a detection limit of 7×10,5,M. Similarly, the TR-induced formation of 1, and its association with the boronic acid ligand allowed a quantitative assay of TR to be performed. In another configuration, the surface of the ISFET gate was modified with tyramine or 1 to form functional surfaces for analyzing TR activities. The TR-induced oxidation of the tyramine- or 1 -functionalized ISFETs resulted in the formation of the redox-active dopaquinone units. The control of the gate potential by the redox-active dopaquinone units allowed a quantitative assay of TR to be performed. The dopaquinone-functionalized ISFETs could be regenerated to give the 1 -modified sensing devices by treatment with ascorbic acid. [source] Detection of Explosives Using Field-Effect TransistorsELECTROANALYSIS, Issue 20 2009Etery Sharon Abstract The gate surfaces of ion-sensitive field-effect transistor (ISFET) devices were functionalized with the ,-donor units, 6-hydroxydopamine (1) or 4-aminothiophenol (2). Concentration of trinitrotoluene, TNT, on the gate via ,-donor-acceptor interactions yields charge-transfer complexes that alter the gate potential. This enables the label-free analysis of TNT with a detection limit corresponding to 1×10,7,M. [source] Sensing with Nafion Coated Carbon Nanotube Field-Effect TransistorsELECTROANALYSIS, Issue 1-2 2004Alexander Star Abstract Sequential CVD and CMOS processes were used to make a FET that has single walled carbon nanotubes to serve as the conducting source to drain channel. This structure can be decorated to provide gas and liquid responses and herein is evaluated as a humdity sensor. The Na+, K+, and Ca2+ ion-exchanged Nafion polymer acts as the chemically sensitive layer in this electrochemical sensor. The effect of gate voltage on the charge-sensitive NT structure was found to be RH dependent over the range of 12,93% RH with msec response time. [source] Organic Electronics: High Tg Cyclic Olefin Copolymer Gate Dielectrics for N,N,-Ditridecyl Perylene Diimide Based Field-Effect Transistors: Improving Performance and Stability with Thermal Treatment (Adv. Funct.ADVANCED FUNCTIONAL MATERIALS, Issue 16 2010Mater. Abstract A novel application of ethylene-norbornene cyclic olefin copolymers (COC) as gate dielectric layers in organic field-effect transistors (OFETs) that require thermal annealing as a strategy for improving the OFET performance and stability is reported. The thermally-treated N,N, -ditridecyl perylene diimide (PTCDI-C13)-based n-type FETs using a COC/SiO2 gate dielectric show remarkably enhanced atmospheric performance and stability. The COC gate dielectric layer displays a hydrophobic surface (water contact angle = 95° ± 1°) and high thermal stability (glass transition temperature = 181 °C) without producing crosslinking. After thermal annealing, the crystallinity improves and the grain size of PTCDI-C13 domains grown on the COC/SiO2 gate dielectric increases significantly. The resulting n-type FETs exhibit high atmospheric field-effect mobilities, up to 0.90 cm2 V,1 s,1 in the 20 V saturation regime and long-term stability with respect to H2O/O2 degradation, hysteresis, or sweep-stress over 110 days. By integrating the n-type FETs with p-type pentacene-based FETs in a single device, high performance organic complementary inverters that exhibit high gain (exceeding 45 in ambient air) are realized. [source] High Tg Cyclic Olefin Copolymer Gate Dielectrics for N,N,-Ditridecyl Perylene Diimide Based Field-Effect Transistors: Improving Performance and Stability with Thermal TreatmentADVANCED FUNCTIONAL MATERIALS, Issue 16 2010Jaeyoung Jang Abstract A novel application of ethylene-norbornene cyclic olefin copolymers (COC) as gate dielectric layers in organic field-effect transistors (OFETs) that require thermal annealing as a strategy for improving the OFET performance and stability is reported. The thermally-treated N,N, -ditridecyl perylene diimide (PTCDI-C13)-based n-type FETs using a COC/SiO2 gate dielectric show remarkably enhanced atmospheric performance and stability. The COC gate dielectric layer displays a hydrophobic surface (water contact angle = 95° ± 1°) and high thermal stability (glass transition temperature = 181 °C) without producing crosslinking. After thermal annealing, the crystallinity improves and the grain size of PTCDI-C13 domains grown on the COC/SiO2 gate dielectric increases significantly. The resulting n-type FETs exhibit high atmospheric field-effect mobilities, up to 0.90 cm2 V,1 s,1 in the 20 V saturation regime and long-term stability with respect to H2O/O2 degradation, hysteresis, or sweep-stress over 110 days. By integrating the n-type FETs with p-type pentacene-based FETs in a single device, high performance organic complementary inverters that exhibit high gain (exceeding 45 in ambient air) are realized. [source] Organic Field-Effect Transistors: Planarization of Polymeric Field-Effect Transistors: Improvement of Nanomorphology and Enhancement of Electrical Performance (Adv. Funct.ADVANCED FUNCTIONAL MATERIALS, Issue 14 2010Mater. Contact geometry plays an important role in charge injection and transport in organic field-effect transistors. On page 2216, T. Kowalewski, L. M. Porter, et al. show a dramatic effect of electrode planarization on the polymer morphology at the contact edges and a resulting increase in fi eld-effect mobility in short channel length devices, and a corresponding decrease in contact resistance. The cover image shows atomic force micrograph of individual polymer nanofi brils spanning the length of a 10 µm channel transistor with planarized contacts. [source] Planarization of Polymeric Field-Effect Transistors: Improvement of Nanomorphology and Enhancement of Electrical PerformanceADVANCED FUNCTIONAL MATERIALS, Issue 14 2010Kumar A. Singh Abstract The planarization of bottom-contact organic field-effect transistors (OFETs) resulting in dramatic improvement in the nanomorphology and an associated enhancement in charge injection and transport is reported. Planar OFETs based on regioregular poly(3-hexylthiophene) (rr-P3HT) are fabricated wherein the Au bottom-contacts are recessed completely in the gate-dielectric. Normal OFETs having a conventional bottom-contact configuration with 50-nm-high contacts are used for comparison purpose. A modified solvent-assisted drop-casting process is utilized to form extremely thin rr-P3HT films. This process is critical for direct visualization of the effect of planarization on the polymer morphology. Atomic force micrographs (AFM) show that in a normal OFET the step between the surface of the contacts and the gate dielectric disrupts the self-assembly of the rr-P3HT film, resulting in poor morphology at the contact edges. The planarization of contacts results in notable improvement of the nanomorphology of rr-P3HT, resulting in lower resistance to charge injection. However, an improvement in field-effect mobility is observed only at short channel lengths. AFM shows the presence of well-ordered nanofibrils extending over short channel lengths. At longer channel lengths the presence of grain boundaries significantly minimizes the effect of improvement in contact geometry as the charge transport becomes channel-limited. [source] Emission Color Tuning in Ambipolar Organic Single-Crystal Field-Effect Transistors by Dye-DopingADVANCED FUNCTIONAL MATERIALS, Issue 10 2010Hajime Nakanotani Abstract The effect of dye-doping in ambipolar light-emitting organic field-effect transistors (LE-OFETs) is investigated from the standpoint of the carrier mobilities and the electroluminescence (EL) characteristics under ambipolar operation. Dye-doping of organic crystals permits not only tuning of the emission color but also significantly increases the efficiency of ambipolar LE-OFETs. A rather high external EL quantum efficiency (,0.64%) of one order of magnitude higher than that of a pure p -distyrylbenzene (P3V2) single crystal is obtained by tetracene doping. The doping of tetracene molecules into a host P3V2 crystal has almost no effect on the electron mobility and the dominant carrier recombination process in the tetracene-doped P3V2 crystal involves direct carrier recombination on the tetracene molecules. [source] Dual-Gate Organic Field-Effect Transistors as Potentiometric Sensors in Aqueous SolutionADVANCED FUNCTIONAL MATERIALS, Issue 6 2010Mark-Jan Spijkman Abstract Buried electrodes and protection of the semiconductor with a thin passivation layer are used to yield dual-gate organic transducers. The process technology is scaled up to 150-mm wafers. The transducers are potentiometric sensors where the detection relies on measuring a shift in the threshold voltage caused by changes in the electrochemical potential at the second gate dielectric. Analytes can only be detected within the Debye screening length. The mechanism is assessed by pH measurements. The threshold voltage shift depends on pH as ,Vth,=,(Ctop/Cbottom),×,58,mV per pH unit, indicating that the sensitivity can be enhanced with respect to conventional ion-sensitive field-effect transistors (ISFETs) by adjusting the ratio of the top and bottom gate capacitances. Remaining challenges and opportunities are discussed. [source] Air-Stable n-Type Organic Field-Effect Transistors Based on Carbonyl-Bridged Bithiazole DerivativesADVANCED FUNCTIONAL MATERIALS, Issue 6 2010Yutaka Ie Abstract An electronegative conjugated compound composed of a newly designed carbonyl-bridged bithiazole unit and trifluoroacetyl terminal groups is synthesized as a candidate for air-stable n-type organic field-effect transistor (OFET) materials. Cyclic voltammetry measurements reveal that carbonyl-bridging contributes both to lowering the lowest unoccupied molecular orbital energy level and to stabilizing the anionic species. X-ray crystallographic analysis of the compound shows a planar molecular geometry and a dense molecular packing, which is advantageous to electron transport. Through these appropriate electrochemical properties and structures for n-type semiconductor materials, OFET devices based on this compound show electron mobilities as high as 0.06,cm2 V,1 s,1 with on/off ratios of 106 and threshold voltages of 20,V under vacuum conditions. Furthermore, these devices show the same order of electron mobility under ambient conditions. [source] Solution Processable Fluorenyl Hexa- peri -hexabenzocoronenes in Organic Field-Effect Transistors and Solar CellsADVANCED FUNCTIONAL MATERIALS, Issue 6 2010Wallace W. H. Wong Abstract The organization of organic semiconductor molecules in the active layer of organic electronic devices has important consequences to overall device performance. This is due to the fact that molecular organization directly affects charge carrier mobility of the material. Organic field-effect transistor (OFET) performance is driven by high charge carrier mobility while bulk heterojunction (BHJ) solar cells require balanced hole and electron transport. By investigating the properties and device performance of three structural variations of the fluorenyl hexa- peri -hexabenzocoronene (FHBC) material, the importance of molecular organization to device performance was highlighted. It is clear from 1H NMR and 2D wide-angle X-ray scattering (2D WAXS) experiments that the sterically demanding 9,9-dioctylfluorene groups are preventing ,,, intermolecular contact in the hexakis-substituted FHBC 4. For bis-substituted FHBC compounds 5 and 6, ,,, intermolecular contact was observed in solution and hexagonal columnar ordering was observed in solid state. Furthermore, in atomic force microscopy (AFM) experiments, nanoscale phase separation was observed in thin films of FHBC and [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) blends. The differences in molecular and bulk structural features were found to correlate with OFET and BHJ solar cell performance. Poor OFET and BHJ solar cells devices were obtained for FHBC compound 4 while compounds 5 and 6 gave excellent devices. In particular, the field-effect mobility of FHBC 6, deposited by spin-casting, reached 2.8,×,10,3,cm2 V,1 s and a power conversion efficiency of 1.5% was recorded for the BHJ solar cell containing FHBC 6 and PC61BM. [source] Controllable Shifts in Threshold Voltage of Top-Gate Polymer Field-Effect Transistors for Applications in Organic Nano Floating Gate MemoryADVANCED FUNCTIONAL MATERIALS, Issue 2 2010Kang-Jun Baeg Abstract Organic field-effect transistor (FET) memory is an emerging technology with the potential to realize light-weight, low-cost, flexible charge storage media. Here, solution-processed poly[9,9-dioctylfluorenyl-2,7-diyl]-co-(bithiophene)] (F8T2) nano floating gate memory (NFGM) with a top-gate/bottom-contact device configuration is reported. A reversible shift in the threshold voltage (VTh) and reliable memory characteristics was achieved by the incorporation of thin Au nanoparticles (NPs) as charge storage sites for negative charges (electrons) at the interface between polystyrene and cross-linked poly(4-vinylphenol). The F8T2 NFGM showed relatively high field-effect mobility (µFET) (0.02,cm2 V,1 s,1) for an amorphous semiconducting polymer with a large memory window (ca. 30,V), a high on/off ratio (more than 104) during writing and erasing with an operation voltage of 80,V of gate bias in a relatively short timescale (less than 1,s), and a retention time of a few hours. This top-gated polymer NFGM could be used as an organic transistor memory element for organic flash memory. [source] Polymer Field-Effect Transistors Fabricated by the Sequential Gravure Printing of Polythiophene, Two Insulator Layers, and a Metal Ink GateADVANCED FUNCTIONAL MATERIALS, Issue 2 2010Monika M. Voigt Abstract The mass production technique of gravure contact printing is used to fabricate state-of-the art polymer field-effect transistors (FETs). Using plastic substrates with prepatterned indium tin oxide source and drain contacts as required for display applications, four different layers are sequentially gravure-printed: the semiconductor poly(3-hexylthiophene-2,5-diyl) (P3HT), two insulator layers, and an Ag gate. A crosslinkable insulator and an Ag ink are developed which are both printable and highly robust. Printing in ambient and using this bottom-contact/top-gate geometry, an on/off ratio of >104 and a mobility of 0.04,cm2 V,1 s,1 are achieved. This rivals the best top-gate polymer FETs fabricated with these materials. Printing using low concentration, low viscosity ink formulations, and different P3HT molecular weights is demonstrated. The printing speed of 40,m min,1 on a flexible polymer substrate demonstrates that very high-volume, reel-to-reel production of organic electronic devices is possible. [source] Variable Temperature Mobility Analysis of n-Channel, p-Channel, and Ambipolar Organic Field-Effect TransistorsADVANCED FUNCTIONAL MATERIALS, Issue 1 2010Joseph A. Letizia Abstract The temperature dependence of field-effect transistor (FET) mobility is analyzed for a series of n-channel, p-channel, and ambipolar organic semiconductor-based FETs selected for varied semiconductor structural and device characteristics. The materials (and dominant carrier type) studied are 5,5,,,-bis(perfluorophenacyl)-2,2,:5,,2,:5,,2,,,-quaterthiophene (1, n-channel), 5,5,,,-bis(perfluorohexyl carbonyl)-2,2,:5,,2,:5,,2,,,-quaterthiophene (2, n-channel), pentacene (3, p-channel); 5,5,,,-bis(hexylcarbonyl)-2,2,:5,,2,:5,,2,,,-quaterthiophene (4, ambipolar), 5,5,,,-bis-(phenacyl)-2,2,: 5,,2,:5,,2,,,-quaterthiophene (5, p-channel), 2,7-bis((5-perfluorophenacyl)thiophen-2-yl)-9,10-phenanthrenequinone (6, n-channel), and poly(N -(2-octyldodecyl)-2,2,-bithiophene-3,3,-dicarboximide) (7, n-channel). Fits of the effective field-effect mobility (µeff) data assuming a discrete trap energy within a multiple trapping and release (MTR) model reveal low activation energies (EAs) for high-mobility semiconductors 1,3 of 21, 22, and 30,meV, respectively. Higher EA values of 40,70,meV are exhibited by 4,7 -derived FETs having lower mobilities (µeff). Analysis of these data reveals little correlation between the conduction state energy level and EA, while there is an inverse relationship between EA and µeff. The first variable-temperature study of an ambipolar organic FET reveals that although n-channel behavior exhibits EA,=,27,meV, the p-channel regime exhibits significantly more trapping with EA,=,250,meV. Interestingly, calculated free carrier mobilities (µ0) are in the range of ,0.2,0.8,cm2,V,1 s,1 in this materials set, largely independent of µeff. This indicates that in the absence of charge traps, the inherent magnitude of carrier mobility is comparable for each of these materials. Finally, the effect of temperature on threshold voltage (VT) reveals two distinct trapping regimes, with the change in trapped charge exhibiting a striking correlation with room temperature µeff. The observation that EA is independent of conduction state energy, and that changes in trapped charge with temperature correlate with room temperature µeff, support the applicability of trap-limited mobility models such as a MTR mechanism to this materials set. [source] Sensing of Alkylating Agents Using Organic Field-Effect TransistorsADVANCED FUNCTIONAL MATERIALS, Issue 1 2010Yair Gannot Abstract Alkylating agents are simple and reactive molecules that are commonly used in many and diverse fields, such as organic synthesis, medicine, and agriculture. Some highly reactive alkylating species are also being used as blister chemical warfare agents. The detection and identification of alkylating agent is not a trivial issue because of their high reactivity and simple structure. Here, a novel polythiophene derivative that is capable of reacting with alkylating agents is reported, along with its application in direct electrical sensing of alkylators using an organic field-effect transistor, OFET, device. Upon reacting with alkylators, the OFET containing the new polythiophene analogue as its channel becomes conductive, and the gate effect is lost; this is in marked contrast to the response of the OFET to "innocent" vapors, such as alcohols and acetone. By following the drain,source current under gate bias, one can easily follow the processes of absorption of the analyte to the polythiophene channel and their subsequent reaction. [source] Metastable Copper-Phthalocyanine Single-Crystal Nanowires and Their Use in Fabricating High-Performance Field-Effect TransistorsADVANCED FUNCTIONAL MATERIALS, Issue 23 2009Kai Xiao Abstract This paper describes a simple, vapor-phase route for the synthesis of metastable , -phase copper-phthalocyanine (CuPc) single-crystal nanowires through control of the growth temperature. The influence of the growth temperature on the crystal structures, morphology, and size of the CuPc nanostructures is explored using X-ray diffraction (XRD), optical absorption, and transmission electron microscopy (TEM). , -CuPc nanowires are successfully incorporated as active semiconductors in field-effect transistors (FETs). Single nanowire devices exhibit carrier mobilities and current on/off ratios as high as 0.4,cm2 V,1 s,1 and >104, respectively. [source] Insulator Polarization Mechanisms in Polyelectrolyte-Gated Organic Field-Effect TransistorsADVANCED FUNCTIONAL MATERIALS, Issue 20 2009Oscar Larsson Abstract Electrolyte-gated organic field-effect transistors (OFETs) hold promise for robust printed electronics operating at low voltages. The polarization mechanism of thin solid electrolyte films, the gate insulator in such OFETs, is still unclear and appears to limit the transient current characteristics of the transistors. Here, the polarization response of a thin proton membrane, a poly(styrenesulfonic acid) film, is controlled by varying the relative humidity. The formation of the conducting transistor channel follows the polarization of the polyelectrolyte, such that the drain transient current characteristics versus the time are rationalized by three different polarization mechanisms: the dipolar relaxation at high frequencies, the ionic relaxation (migration) at intermediate frequencies, and the electric double-layer formation at the polyelectrolyte interfaces at low frequencies. The electric double layers of polyelectrolyte capacitors are formed in ,1,µs at humid conditions and an effective capacitance per area of 10,µF cm,2 is obtained at 1,MHz, thus suggesting that this class of OFETs might operate at up to 1,MHz at 1,V. [source] Controlling Electron and Hole Charge Injection in Ambipolar Organic Field-Effect Transistors by Self-Assembled MonolayersADVANCED FUNCTIONAL MATERIALS, Issue 15 2009Xiaoyang Cheng Abstract Controlling contact resistance in organic field-effect transistors (OFETs) is one of the major hurdles to achieve transistor scaling and dimensional reduction. In particular in the context of ambipolar and/or light-emitting OFETs it is a difficult challenge to obtain efficient injection of both electrons and holes from one injecting electrode such as gold since organic semiconductors have intrinsically large band gaps resulting in significant injection barrier heights for at least one type of carrier. Here, systematic control of electron and hole contact resistance in poly(9,9-di- n -octylfluorene- alt -benzothiadiazole) ambipolar OFETs using thiol-based self-assembled monolayers (SAMs) is demonstrated. In contrast to common believe, it is found that for a certain SAM the injection of both electrons and holes can be improved. This simultaneous enhancement of electron and hole injection cannot be explained by SAM-induced work-function modifications because the surface dipole induced by the SAM on the metal surface lowers the injection barrier only for one type of carrier, but increases it for the other. These investigations reveal that other key factors also affect contact resistance, including i) interfacial tunneling through the SAM, ii) SAM-induced modifications of interface morphology, and iii) the interface electronic structure. Of particular importance for top-gate OFET geometry is iv) the active polymer layer thickness that dominates the electrode/polymer contact resistance. Therefore, a consistent explanation of how SAM electrode modification is able to improve both electron and hole injection in ambipolar OFETs requires considering all mentioned factors. [source] Enhanced Performance of Fullerene n-Channel Field-Effect Transistors with Titanium Sub-Oxide Injection LayerADVANCED FUNCTIONAL MATERIALS, Issue 9 2009Shinuk Cho Abstract Enhanced performance of n-channel organic field-effect transistors (OFETs) is demonstrated by introducing a titanium sub-oxide (TiOx) injection layer. The n-channel OFETs utilize [6,6]-phenyl-C61 butyric acid methyl ester (PC61BM) or [6,6]-phenyl-C71 butyric acid methyl ester (PC71BM) as the semiconductor in the channel. With the TiOx injection layer, the electron mobilities of PC61BM and PC71BM FET using Al as source/drain electrodes are comparable to those obtained from OFETs using Ca as the source/drain electrodes. Direct measurement of contact resistance (Rc) shows significantly decreased Rc values for FETs with the TiOx layer. Ultraviolet photoelectron spectroscopy (UPS) studies demonstrate that the TiOx layer reduces the electron injection barrier because of the relatively strong interfacial dipole of TiOx. In addition to functioning as an electron injection layer that eliminates the contact resistance, the TiOx layer acts as a passivation layer that prevents penetration of O2 and H2O; devices with the TiOx injection layer exhibit a significant improvement in lifetime when exposed to air. [source] Detailed Characterization of Contact Resistance, Gate-Bias-Dependent Field-Effect Mobility, and Short-Channel Effects with Microscale Elastomeric Single-Crystal Field-Effect TransistorsADVANCED FUNCTIONAL MATERIALS, Issue 8 2009Colin Reese No abstract is available for this article. [source] Detailed Characterization of Contact Resistance, Gate-Bias-Dependent Field-Effect Mobility, and Short-Channel Effects with Microscale Elastomeric Single-Crystal Field-Effect TransistorsADVANCED FUNCTIONAL MATERIALS, Issue 5 2009Colin Reese Abstract The organic field-effect transistor (OFET) has proven itself invaluable as both the fundamental element in organic circuits and the primary tool for the characterization of novel organic electronic materials. Crucial to the success of the OFET in each of these venues is a working understanding of the device physics that manifest themselves in the form of electrical characteristics. As commercial applications shift to smaller device dimensions and structure/property relationships become more refined, the understanding of these phenomena become increasingly critical. Here, we employ high-performance, elastomeric, photolithographically patterned single-crystal field-effect transistors as tools for the characterization of short-channel effects and bias-dependent parasitic contact resistance and field-effect mobility. Redundant characterization of devices at multiple channel lengths under a single crystal allow the morphology-free analysis of these effects, which is carried out in the context of a device model previously reported. The data show remarkable consistency with our model, yielding fresh insight into each of these phenomena, as well as confirming the utility of our FET design. [source] Monitoring the Channel Formation in Organic Field-Effect Transistors via Photoinduced Charge TransferADVANCED FUNCTIONAL MATERIALS, Issue 5 2009Thokchom Birendra Singh Abstract Conducting channel formation in organic field-effect transistors (OFETs) is considered to happen in the organic semiconductor layer very close to the interface with the gate dielectric. In the gradual channel approximation, the local density of accumulated charge carriers varies as a result of applied gate bias, with the majority of the charge carriers being localized in the first few semiconductor monolayers close to the dielectric interface. In this report, a new concept is employed which enables the accumulation of charge carriers in the channel by photoinduced charge transfer. An OFET employing C60 as a semiconductor and divinyltetramethyldisiloxane-bis(benzocyclobutene) as the gate dielectric is modified by a very thin noncontinuous layer of zinc-phthalocyanine (ZnPc) at the semiconductor/dielectric interface. With this device geometry, it is possible to excite the phthalocyanine selectively and photogenerate charges directly at the semiconductor/dielectric interface via photoinduced electron transfer from ZnPc onto C60. Thus the formation of a gate induced and a photoinduced channel in the same device can be correlated. [source] Ambipolar Organic Field-Effect Transistors from Cross-Conjugated Aromatic Quaterthiophenes; Comparisons with Quinoidal Parent MaterialsADVANCED FUNCTIONAL MATERIALS, Issue 3 2009Rocío Ponce Ortiz Abstract This contribution presents an electrochemical, Raman spectroscopic, and theoretical study probing the differences in molecular and electronic structure of two quinoidal oligothiophenes (3,,4,-dibutyl-5,5,-bis(dicyanomethylene)-5,5,-dihydro-2,2,:5,,2,-terthiophene and 5,5,-bis(dicyanomethylene)-3-hexyl-2,5-dihydro-4,4,-dihexyl-2,2,,5,5,-tetrahydro-tetrathiophene) with terminal tetracyanomethylene functionalization and aromatic oligothiophenes where acceptor moieties are positioned at lateral positions along the conjugated chain (6,6,-dibutylsulfanyl-[2,2,-bi-[4-dicyanovinylene-4H-cyclopenta[2,1-b:3,4-b,]dithiophene]). In this way, the consequences of linear and cross conjugation are compared and contrasted. From this analysis, it is apparent that organic field-effect transistors fabricated with cross-conjugated tetrathiophene semiconductors should combine the benefits of an electron-donor aromatic chain with strongly electron-accepting tetracyanomethylene substituents. The corresponding organic field-effect transistors exhibit ambipolar transport with rather similar hole and electron mobilities. Moreover, n-channel conduction is enhanced to yield one of the highest electron mobilities found to date for this type of material. [source] Room-Temperature Self-Organizing Characteristics of Soluble Acene Field-Effect Transistors,ADVANCED FUNCTIONAL MATERIALS, Issue 4 2008Wi Hyoung Lee We report on the room-temperature self-organizing characteristics of thin films of the organic small-molecule semiconductor triethylsilylethynyl-anthradithiophene (TES-ADT) and its effect on the electrical properties of TES-ADT-based field-effect transistors (FETs). The morphology of TES-ADT films changed dramatically with time, and the field-effect mobility of FETs based on these films increased about 100-fold after seven days as a result of the change in molecular orientation from a tilted structure in the as-prepared film to a well-oriented structure in the final film. We found that the molecular movement is large enough to induce a conformational change to an energetically stable state in spin-coated TES-ADT films, because TES-ADT has a low glass-transition temperature (around room temperature). Our findings demonstrate that organic small-molecule semiconductors that exhibit a low crystallinity immediately after spin-coating can be changed into highly crystalline structures by spontaneous self-organization of the molecules at room temperature, which results in improved electrical properties of FETs based on these semiconductors. [source] | |||||||||||||||||||||||||||||||