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Gate Dielectric (gate + dielectric)
Selected AbstractsHigh-Performance Flexible Transparent Thin-Film Transistors Using a Hybrid Gate Dielectric and an Amorphous Zinc Indium Tin Oxide ChannelADVANCED MATERIALS, Issue 21 2010Jun Liu High-performance flexible transparent thin-film transistors (TFTs) are demonstrated using amorphous zink indium tin oxide (ZITO) transparent oxide conductor electrodes, an amorphous ZITO transparent oxide semiconductor channel, and a vapor-deposited self-assembled nanodielectric (v-SAND) gate insulator. These TFTs exhibit a large field-effect mobility of 110 cm2V,1s,1, a current on/off ratio of 104, and a low operating voltage of 1.0,V, along with very good optical transparency and mechanical flexibility. [source] Vertical Transistor with Ultrathin Silicon Nitride Gate DielectricADVANCED MATERIALS, Issue 44 2009Maryam Moradi Nanoscale vertical thin-film transistors (VTFTs) are fabricated employing a new ultrathin silicon nitride (SiNx) gate dielectric for applications in high-resolution active matrix flat panel electronics. Illustrated are the cross-section schematic and SEM image of a 500,nm channel length VTFT with a 50,nm thick SiNx gate dielectric. The device demonstrates excellent gate control with gate leakage as low as 0.1,nA cm,2. [source] Utilizing Highly Crystalline Pyroelectric Material as Functional Gate Dielectric in Organic Thin-Film TransistorsADVANCED MATERIALS, Issue 8 2009Nguyen Thanh Tien Highly crystalline P(VDF-TrFE) materials have a large remnant polarization that causes the ID,VD curves to have no current saturation in the region where they normally would. This high crystallinity also results in a positive pyroelectricity, which is different from the conventional low response and nonlinear negative pyroelectricity. [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] High K Capacitors and OFET Gate Dielectrics from Self-Assembled BaTiO3 and (Ba,Sr)TiO3 Nanocrystals in the Superparaelectric LimitADVANCED FUNCTIONAL MATERIALS, Issue 4 2010Limin Huang Abstract Nanodielectrics is an emerging field with applications in capacitors, gate dielectrics, energy storage, alternatives to Li-ion batteries, and frequency modulation in communications devices. Self-assembly of high k dielectric nanoparticles is a highly attractive means to produce nanostructured films with improved performance,namely dielectric tunability, low leakage, and low loss,as a function of size, composition, and structure. One of the major challenges is conversion of the nanoparticle building block into a reliable thin film device at conditions consistent with integrated device manufacturing or plastic electronics. Here, the development of BaTiO3 and (Ba,Sr)TiO3 superparaelectric uniform nanocrystal (8,12,nm) films prepared at room temperature by evaporative driven assembly with no annealing step is reported. Thin film inorganic and polymer composite capacitors show dielectric constants in the tunable range of 10,30, dependent on composition, and are confirmed to be superparaelectric. Organic thin film transistor (TFT) devices on flexible substrates demonstrate the readiness of nanoparticle-assembled films as gate dielectrics in device fabrication. [source] Organic Thin Film Transistors with Polymer Brush Gate Dielectrics Synthesized by Atom Transfer Radical PolymerizationADVANCED FUNCTIONAL MATERIALS, Issue 1 2008C. Pinto Abstract Low operating voltage is an important requirement that must be met for industrial adoption of organic field-effect transistors (OFETs). We report here solution fabricated polymer brush gate insulators with good uniformity, low surface roughness and high capacitance. These ultra thin polymer films, synthesized by atom transfer radical polymerization (ATRP), were used to fabricate low voltage OFETs with both evaporated pentacene and solution deposited poly(3-hexylthiophene). The semiconductor-dielectric interfaces in these systems were studied with a variety of methods including scanning force microscopy, grazing incidence X-ray diffraction and neutron reflectometry. These studies highlighted key differences between the surfaces of brush and spun cast polymethyl methacrylate (PMMA) films. [source] Surface-Modified High- k Oxide Gate Dielectrics for Low-Voltage High-Performance Pentacene Thin-Film Transistors,ADVANCED FUNCTIONAL MATERIALS, Issue 6 2007S. Kim Abstract In this study, pentacene thin-film transistors (TFTs) operating at low voltages with high mobilities and low leakage currents are successfully fabricated by the surface modification of the CeO2,SiO2 gate dielectrics. The surface of the gate dielectric plays a crucial role in determining the performance and electrical reliability of the pentacene TFTs. Nearly hysteresis-free transistors are obtained by passivating the devices with appropriate polymeric dielectrics. After coating with poly(4-vinylphenol) (PVP), the reduced roughness of the surface induces the formation of uniform and large pentacene grains; moreover, ,OH groups on CeO2,SiO2 are terminated by C6H5, resulting in the formation of a more hydrophobic surface. Enhanced pentacene quality and reduced hysteresis is observed in current,voltage (I,V) measurements of the PVP-coated pentacene TFTs. Since grain boundaries and ,OH groups are believed to act as electron traps, an OH-free and smooth gate dielectric leads to a low trap density at the interface between the pentacene and the gate dielectric. The realization of electrically stable devices that can be operated at low voltages makes the OTFTs excellent candidates for future flexible displays and electronics applications. [source] Comparison of the Mobility,Carrier Density Relation in Polymer and Single-Crystal Organic Transistors Employing Vacuum and Liquid Gate DielectricsADVANCED MATERIALS, Issue 21 2009Yu Xia The mobility of polymer and single-crystal transistors using a universal test-bed where the injected carrier density can vary more than four orders of magnitude are investigated and compared. A striking difference in the mobility,carrier density relationship was observed, revealing a fundamentally different charge-transport mechanism between polymer and single-crystal transistors. [source] Polymer/YOx Hybrid-Sandwich Gate Dielectrics for Semitransparent Pentacene Thin-Film Transistors Operating Under 5,V,ADVANCED MATERIALS, Issue 17 2006K. Hwang A hybrid-sandwich dielectric,combining the advantages of inorganic high-dielectric-constant dielectrics and ultrathin organic dielectrics,for the gate of pentacene thin-film transistors (TFTs, see figure) is presented. The performance of the TFTs and resistance-load inverters constructed with them is shown to be satisfactory even when the devices are operated at the low voltage of ,5,V. [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] 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] 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] Alkyl-Chain-Length-Independent Hole Mobility via Morphological Control with Poly(3-alkylthiophene) NanofibersADVANCED FUNCTIONAL MATERIALS, Issue 5 2010Wibren D. Oosterbaan Abstract The field-effect transistor (FET) and diode characteristics of poly(3-alkylthiophene) (P3AT) nanofiber layers deposited from nanofiber dispersions are presented and compared with those of layers deposited from molecularly dissolved polymer solutions in chlorobenzene. The P3AT n -alkyl-side-chain length was varied from 4 to 9 carbon atoms. The hole mobilities are correlated with the interface and bulk morphology of the layers as determined by UV,vis spectroscopy, transmission electron microscopy (TEM) with selected area electron diffraction (SAED), atomic force microscopy (AFM), and polarized carbon K -edge near edge X-ray absorption fine structure (NEXAFS) spectroscopy. The latter technique reveals the average polymer orientation in the accumulation region of the FET at the interface with the SiO2 gate dielectric. The previously observed alkyl-chain-length-dependence of the FET mobility in P3AT films results from differences in molecular ordering and orientation at the dielectric/semiconductor interface, and it is concluded that side-chain length does not determine the intrinsic mobility of P3ATs, but rather the alkyl chain length of P3ATs influences FET diode mobility only through changes in interfacial bulk ordering in solution processed films. [source] Printed Sub-2 V Gel-Electrolyte-Gated Polymer Transistors and CircuitsADVANCED FUNCTIONAL MATERIALS, Issue 4 2010Yu Xia Abstract The fabrication and characterization of printed ion-gel-gated poly(3-hexylthiophene) (P3HT) transistors and integrated circuits is reported, with emphasis on demonstrating both function and performance at supply voltages below 2,V. The key to achieving fast sub-2,V operation is an unusual gel electrolyte based on an ionic liquid and a gelating block copolymer. This gel electrolyte serves as the gate dielectric and has both a short polarization response time (<1,ms) and a large specific capacitance (>10,µF cm,2), which leads simultaneously to high output conductance (>2,mS mm,1), low threshold voltage (<1,V) and high inverter switching frequencies (1,10,kHz). Aerosol-jet-printed inverters, ring oscillators, NAND gates, and flip-flop circuits are demonstrated. The five-stage ring oscillator operates at frequencies up to 150,Hz, corresponding to a propagation delay of 0.7 ms per stage. These printed gel electrolyte gated circuits compare favorably with other reported printed circuits that often require much larger operating voltages. Materials factors influencing the performance of the devices are discussed. [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] Orders-of-Magnitude Reduction of the Contact Resistance in Short-Channel Hot Embossed Organic Thin Film Transistors by Oxidative Treatment of Au-Electrodes,ADVANCED FUNCTIONAL MATERIALS, Issue 15 2007B. Stadlober Abstract In this study we report on the optimization of the contact resistance by surface treatment in short-channel bottom-contact OTFTs based on pentacene as semiconductor and SiO2 as gate dielectric. The devices have been fabricated by means of nanoimprint lithography with channel lengths in the range of 0.3,,m,<,L,<,3.0,,m. In order to reduce the contact resistance the Au source- and drain-contacts were subjected to a special UV/ozone treatment, which induced the formation of a thin AuOx layer. It turned out, that the treatment is very effective (i),in decreasing the hole-injection barrier between Au and pentacene and (ii),in improving the morphology of pentacene on top of the Au contacts and thus reducing the access resistance of carriers to the channel. Contact resistance values as low as 80,,,cm were achieved for gate voltages well above the threshold. In devices with untreated contacts, the charge carrier mobility shows a power-law dependence on the channel length, which is closely related to the contact resistance and to the grain-size of the pentacene crystallites. Devices with UV/ozone treated contacts of very low resistance, however, exhibit a charge carrier mobility in the range of 0.3,cm2,V,1,s,1,<,,,<,0.4,cm2,V,1,s,1 independent of the channel length. [source] Surface-Modified High- k Oxide Gate Dielectrics for Low-Voltage High-Performance Pentacene Thin-Film Transistors,ADVANCED FUNCTIONAL MATERIALS, Issue 6 2007S. Kim Abstract In this study, pentacene thin-film transistors (TFTs) operating at low voltages with high mobilities and low leakage currents are successfully fabricated by the surface modification of the CeO2,SiO2 gate dielectrics. The surface of the gate dielectric plays a crucial role in determining the performance and electrical reliability of the pentacene TFTs. Nearly hysteresis-free transistors are obtained by passivating the devices with appropriate polymeric dielectrics. After coating with poly(4-vinylphenol) (PVP), the reduced roughness of the surface induces the formation of uniform and large pentacene grains; moreover, ,OH groups on CeO2,SiO2 are terminated by C6H5, resulting in the formation of a more hydrophobic surface. Enhanced pentacene quality and reduced hysteresis is observed in current,voltage (I,V) measurements of the PVP-coated pentacene TFTs. Since grain boundaries and ,OH groups are believed to act as electron traps, an OH-free and smooth gate dielectric leads to a low trap density at the interface between the pentacene and the gate dielectric. The realization of electrically stable devices that can be operated at low voltages makes the OTFTs excellent candidates for future flexible displays and electronics applications. [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] Vertical Transistor with Ultrathin Silicon Nitride Gate DielectricADVANCED MATERIALS, Issue 44 2009Maryam Moradi Nanoscale vertical thin-film transistors (VTFTs) are fabricated employing a new ultrathin silicon nitride (SiNx) gate dielectric for applications in high-resolution active matrix flat panel electronics. Illustrated are the cross-section schematic and SEM image of a 500,nm channel length VTFT with a 50,nm thick SiNx gate dielectric. The device demonstrates excellent gate control with gate leakage as low as 0.1,nA cm,2. [source] Reliability of Organic Field-Effect TransistorsADVANCED MATERIALS, Issue 38-39 2009Henning Sirringhaus Abstract In this article, we review current understanding of the reliability of organic field-effect transistors, with a particular focus on degradation of device characteristics under bias stress conditions. We discuss the various factors that have been found to influence the operational stability of different material systems, including dependence on stress voltage and duty cycle, gate dielectric, environmental conditions, light exposure, and contact resistance. A key question concerns the role of extrinsic factors, such as oxidation or presence of moisture, and that of intrinsic factors, such as the inherent structural and electronic disorder that is present in thin organic semiconductor films. We also review current understanding of the microscopic defects that could play a role in charge trapping in organic semiconductors. [source] Flexible Inorganic/Organic Hybrid Thin-Film Transistors Using All-Transparent Component Materials,ADVANCED MATERIALS, Issue 20 2007L. Wang Inorganic-organic hybrid TFTs have been fabricated at room temperature using IAD-derived high-quality semiconducting In2O3 and a crosslinked spin-coatable polymer gate dielectric. TFTs exhibiting field-effect mobilities up to 160 cm2 V,1 s,1, on Si and 10 cm2 V,1 s,1 on PET substrates have been demonstrated. TFTs on PET combine good transport characteristics as well as optical transparency and flexibility. [source] Thickness Dependence of Mobility in Pentacene Thin-Film Transistors,ADVANCED MATERIALS, Issue 14 2005R. Ruiz The field-effect mobility of pentacene transistors saturates when six,monolayers of pentacene are deposited on the gate dielectric. This saturation is not caused by the formation of islands, as the early stages of growth have been found to take place in a layer-by-layer fashion, and layer completion continues well past six,monolayers (see Figure). [source] Observation of Field-Effect Transistor Behavior at Self-Organized Interfaces,ADVANCED MATERIALS, Issue 18 2004L.-L. Chua Ultrathin, conformal semiconductor, dielectric bilayers can be fabricated in one step by self-organization (see Figure), without exposing the critical interface to ambient contamination. Low-voltage polymer field-effect transistors using a fluorene,triarylamine copolymer as the p-channel semiconductor and 40,60 nm thick crosslinked bisbenzocyclobutene derivative as the gate dielectric are shown to be robust and reproducible. [source] Low-voltage, high-gain, and high-mobility organic complementary inverters based on N,N,-ditridecyl-3,4,9,10-perylenetetracarboxylic diimide and pentacenePHYSICA STATUS SOLIDI - RAPID RESEARCH LETTERS, Issue 2 2008Shuhei Tatemichi Abstract The authors describe an organic complementary inverter with N,N,-ditridecyl-3,4,9,10-perylenetetracarboxylic diimide as an n-type semiconductor and pentacene as a p-type semiconductor. Each transistor of the inverter exhibited high carrier mobility: 1.62 cm2/Vs for an n-type drive transistor and 0.57 cm2/Vs for a p-type switch transistor. The gain of the inverter reached 125. Another inverter using Ta2O5 as a high , gate dielectric performed well with a gain of 500 and an operation voltage of only 5 V. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Dielectric layers for organic field effect transistors as gate dielectric and surface passivationPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 3 2008T. Diekmann Abstract Organic field effect transistors with the organic semiconductor pentacene, using silicon substrates, were successfully built on conventional inorganic dielectrics like silicon dioxide or silicon nitride. They can drive drain currents up to 15 mA. Beyond that, polymer films were investigated as gate dielectrics in order to achieve transistors on plastic films. On polyester substrates with an inorganic,organic gate dielectric, devices reach drain currents comparable to transistors on silicon dioxide and charge carrier mobilities of up to 0.35 cm2/V s. Analysis of the pentacene surface by atomic force microscopy showed pentacene crystallites achieving dimensions of more than 1.5 µm. The unprotected organic devices suffer from degradation due to water and oxygen incorporation. Therefore, the application of a hydrophobic polytetrafluoroethylene layer as capping layer is studied. Because of the reduced influence of water, a shift to positive threshold voltages is caused. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Potentiometry on pentacene OFETs: Charge carrier mobilities and injection barriers in bottom and top contact configurationsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 3 2008R. Scholz Abstract In a combination of experimental techniques including electrical probes, potentiometry, and charge transient spectroscopy (QTS), we develop concepts how to quantify the potential drops at the contacts, the mobility in the channel region, and the density of states of deep traps in pentacene OFETs. For OFETs grown from unpurified pentacene on pre-patterned Au bottom contacts, a comparison between potentiometry and two-dimensional device simulations determines an injection barrier of 0.73 eV at the source contact and a hole mobility of 0.014 cm2 V,1 s,1 in the pentacene channel. Temperature-dependent QTS data reveal a trap level at about 125 meV from the hole transport band, indicating a relatively high density of unintentional dopants and therefore a high background density of majority charge carriers. In OFETs grown from purified pentacene onto a SiO2 gate dielectric and Au top contacts evaporated onto the pentacene channel without breaking the vacuum, potentiometry reveals a nearly perfect alignment of the metal work function with the hole transport level in the organic layer. The much lower density of deep traps in these samples raises the hole mobility to the range 0.1,0.2 cm2 V,1 s,1. A further improvement of the hole mobility and the resulting device performance can be achieved by a chemical treatment of the gate oxide with n-octadecytrichlorosilane (OTS). (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Interface of atomic layer deposited Al2O3 on H-terminated siliconPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 9 2006K. Y. Gao Abstract Al2O3 films 1 to 20 nm thick were deposited as alternative high-, gate dielectric on hydrogen-terminated silicon by Atomic Layer Deposition (ALD) and characterized by Synchrotron X-ray Photoelectron Spec-troscopy (SXPS), Fourier Transform Infrared (FTIR) absorption spectroscopy and admittance measure-ments. The SXPS results indicate that about 60% of the original Si,H surface bonds are preserved at the Al2O3/Si interface and this is confirmed by monitoring the Si,H stretching modes by FTIR spectroscopy in the Attenuated Total Reflection (ATR) mode both before and after ALD of Al2O3. The remaining 40% of Si,H bonds are replaced by Si,O bonds as verified by SXPS. In addition, a fraction of a monolayer of SiO2 forms on top of the Al2O3 dielectric during deposition. The presence of OH-groups at a level of 3% of the total oxygen content was detected throughout the Al2O3 layer through a chemically shifted O 1s component in SXPS. Admittance measurements give a dielectric constant of 9.12, but a relatively high density of interface traps between 1011 and 1012 cm,2 eV,1. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Elasticity, electronic structure, and dielectric property of cubic SrHfO3 from first-principlesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2009Z. F. Hou Abstract Recently, SrHfO3 compound was proposed as a potential gate dielectric to fabricate metal,oxide,semiconductor field-effect transistors (MOSFET) with equivalent oxide thickness (EOT) below 1 nm. Here we report the elasticity, electronic structure, and dielectric property of cubic SrHfO3 from first-principle study based on the plane-wave pseudopotential method within the local density approximation (LDA). The independent elastic constants of cubic SrHfO3 are derived from the derivative of total energy as a function of lattice strain. The elastic modulus is predicted from Voight-Hill bounds. The Born effective charges, electronic dielectric tensors, long wavelength phonon frequencies, and LO,TO splitting of cubic SrHfO3 are computed by linear response with density functional perturbation theory (DFPT). The calculated lattice constant and bulk modulus of cubic SrHfO3 are in good agreement with the available experimental data and other theoretical results. Our results show cubic SrHfO3 is a ductile insulator with an indirect band gap of 3.74 eV (LDA value) and electric dielectric tensor of 4.43, Hf 5d states and O 2p states exhibit a strong hybridization, and cubic SrHfO3 can be mechanically stable. In addition, the phonon frequency of ,soft mode' at zone-center also agrees well with previous theoretical value. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||||||||