ADVANCED FUNCTIONAL MATERIALS, Issue 18 2009
Liqiang Li
Abstract High-performance and battery drivable organic single-crystalline transistors with operational voltages,,,2.0,V are demonstrated using high-quality copper phthalocyanine (CuPc) single-crystalline nanoribbons and ultrathin polymer nanodielectrics. The ultrathin polymer nanodielectric is synthesized by grafting a ca. 10,nm poly(methyl methacrylate) (PMMA) brush on a silicon surface via surface-initiated atom-transfer radical polymerization (SI-ATRP). This surface-grafted nanodielectric exhibits a large capacitance, excellent insulating property, and good compatibility with organic semiconductors. The realization of a low operational voltage for battery driving at high performance, together with the merits of surface grafting of a nanodielectric, as well as the mechanical flexibility of the organic nanoribbon, suggests a bright future for use of these transistors in low-cost and flexible circuits. [source]

High-Performance Flexible Transparent Thin-Film Transistors Using a Hybrid Gate Dielectric and an Amorphous Zinc Indium Tin Oxide Channel

ADVANCED MATERIALS, Issue 21 2010
Jun 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 Dielectric

ADVANCED MATERIALS, Issue 44 2009
Maryam 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 Transistors

ADVANCED MATERIALS, Issue 8 2009
Nguyen 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]

A Novel Temperature-Compensated Microwave Dielectric (1,x)(Mg0.95Ni0.05)TiO3,xCa0.6La0.8/3TiO3 Ceramics System

INTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 5 2009
Chun-Hsu Shen
The microstructure and microwave dielectric properties of a (1,x)(Mg0.95Ni0.05)TiO3,xCa0.6La0.8/3TiO3 ceramics system have been investigated. The system was prepared using a conventional solid-state ceramic route. In order to produce a temperature-stable material, Ca0.6La0.8/3TiO3 was added for a near-zero temperature coefficient (,f). With partial replacement of Mg2+ by Ni2+, the dielectric properties of the (1,x)(Mg0.95Ni0.05)TiO3,xCa0.6La0.8/3TiO3 ceramics can be promoted. The microwave dielectric properties are strongly correlated with the sintering temperature and the composition. An excellent Q × f value of 118,000 GHz can be obtained for the system with x=0.9 at 1325°C. For practical application, a dielectric constant (,r) of 24.61, a Q × f value of 102,000 GHz, and a temperature coefficient of resonant frequency (,f) of ,3.6 ppm/°C for 0.85(Mg0.95Ni0.05)TiO3,0.15Ca0.6La0.8/3TiO3 at 1325°C are proposed. A parallel-coupled line band-pass filter is designed and simulated using the proposed dielectric to study its performance. [source]

Charge Trapping at the Dielectric of Organic Transistors Visualized in Real Time and Space,

ADVANCED MATERIALS, Issue 5 2008

Scanning Kelvin probe microscopy demonstrates that water-induced charge trapping at the SiO2 dielectric , visualized in real time and space , is responsible for the commonly observed gate-bias-induced threshold-voltage shift in organic field-effect transistors. When a bias is applied to the electrodes, charges are injected onto the SiO2 (see background of the figure). When the contacts are grounded, the charges are released again (foreground picture). [source]

A Novel Percolative Ferromagnetic,Ferroelectric Composite with Significant Dielectric and Magnetic Properties,

ADVANCED MATERIALS, Issue 3 2007
Q. Huang
A series of BaTiO3,Ni0.55Zn0.45Fe2.03O4composites are synthesized. The composites exhibit excellent dielectric and magnetic properties in the neighborhood of the percolation threshold,a high dielectric constant that is nearly temperature and frequency independent (see figure),and considerable initial permeability with excellent frequency stability, and may be useful as a high-performance multifunction ceramic composite. [source]

Bi2O3,MoO3 Binary System: An Alternative Ultralow Sintering Temperature Microwave Dielectric

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2009
Di Zhou
Preparation, phase composition, microwave dielectric properties, and chemical compatibility with silver and aluminum electrodes were investigated on a series of single-phase compounds in the Bi2O3,MoO3 binary system. All materials have ultralow sintering temperatures <820°C. Eight different xBi2O3,(1,x)MoO3 compounds between 0.2,x,0.875 were fabricated and the associated microwave dielectric properties were studied. The ,-Bi2Mo2O9 single phase has a positive temperature coefficient of resonant frequency (TCF) about +31 ppm/°C, with a permittivity ,r=38 and Qf=12 500 GHz at 300 K and at a frequency of 6.3 GHz. The ,-Bi2Mo3O12 and ,-Bi2MoO6 compounds both have negative temperature coefficient values of TCF,,215 and ,,114 ppm/°C, with permittivities of ,r=19 and 31, Qf=21 800 and 16 700 GHz at 300 K measured at resonant frequencies of 7.6 and 6.4 GHz, respectively. Through sintering the Bi2O3,2.2MoO3 at 620°C for 2 h, a composite dielectric containing both , and , phase can be obtained with a near-zero temperature coefficient of frequency TCF=,13 ppm/°C and a relative dielectric constant ,r=35, and a large Qf,12 000 GHz is also observed. Owing to the frequent difficulty of thermochemical interactions between low sintering temperature materials and the electrode materials during the cofiring, preliminary investigations are made to determine any major interactions with possible candidate electrode metals, Ag and Al. From the above results, the low sintering temperature, good microwave dielectric properties, chemical compatibility with Al metal electrode, nontoxicity and price advantage of the Bi2O3,MoO3 binary system, all indicate the potential for a new material system with ultralow temperature cofiring for multilayer devices application. [source]

Dielectric and Structural Properties of Layer-Structured Sr1,xCaxBi2Nb2O9

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2008
Shiming Huang
Sr1,xCaxBi2Nb2O9 (x=0, 0.2, 0.4, 0.6, 0.8 and 1) ceramics were prepared by a conventional solid-state reaction method. Their dielectric and structural properties were investigated. X-ray diffraction analysis indicated that single-phase layered perovskites were obtained. For Ca-substituted specimens, a dielectric relaxation peak is observed in the temperature range of 30°,150°C, and there is a broader para-ferroelectric phase transition peak. The temperature of the maximum dielectric constant Tm increases linearly with increasing Ca content. Raman spectra indicate that a small amount of Ca2+ is incorporated into Bi sites in the Bi2O2 layers, and an increase in the degree of distortion of NbO6 octahedra for Ca-substituted specimens should be one of the reasons for the increase in Tm compared with SrBi2Nb2O9. [source]

Electrical Properties of Textured Potassium Strontium Niobate (KSr2Nb5O15) Ceramics Fabricated by Reactive Templated Grain Growth

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2008
Sedat Alkoy
Highly [001] textured KSr2Nb5O15 (KSN) ceramics were fabricated by templated grain growth using acicular KSN template particles (5,15 wt%) and reactive matrix of SrNb2O6 and KNbO3. Excess Nb2O5 (1,1.5 wt%) was added as a liquid former. Increasing sintering temperature and time resulted in increased texture with a maximum texture fraction of 0.98. Dielectric, ferroelectric, and piezoelectric measurements indicate anisotropic properties that are close to single crystal values in the textured ceramics with the highest Pr,18 ,C/cm2, Ps,25 ,C/cm2, and d33=65 pC/N obtained in the c -axis direction. [source]

Structural, Dielectric, and Thermal Properties of Strontium Barium Niobate-Doped Fused Silica Nanocomposites

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2003
Sheng-Guo Lu
Ferroelectric strontium barium niobate (SBN)-doped Na2O,B2O3,SiO2 (NBS) glass nanocomposites were prepared by dispersing sol,gel-derived SBN powder into fused NBS glass. Their structures were characterized by X-ray diffractometry and Raman spectroscopy. The dielectric constants were measured as functions of frequency and temperature using an impedance analyzer. The ferroelectric-to-paraelectric-phase transition was studied by differential scanning calorimetric analysis. Our results revealed that the embedded SBN has lower phase transition temperature and phase transition heat than those of SBN bulk materials. Their activation energy, however, is larger than that of SBN ultra-fine powders. Pure tetragonal-phase SBN nanocomposites can be obtained at annealing temperatures of 750°,1000°C. Their dielectric constants are ,32,46 and ,20,25 at low frequencies and radio frequencies, respectively, and the loss tangent is <0.1 at room temperature in the radio frequencies range. Our studies suggested that additional reduction in the loss properties must be made before these systems can be considered for application as microwave dielectric materials. [source]

Intrinsic Elastic, Dielectric, and Piezoelectric Losses in Lead Zirconate Titanate Ceramics Determined by an Immittance-Fitting Method

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2002
Takaaki Tsurumi
The material coefficients of "soft" and "hard" lead zirconate titanate (PZT) ceramics were determined as complex values by the nonlinear least-squares-fitting of immittance data measured for length-extensional bar resonators. The piezoelectric d -constant should be a complex value to obtain a best fitting between observed and calculated results. Because the elastic, dielectric, and piezoelectric losses determined in this process were not "intrinsic" losses, a calculation process to evaluate the "intrinsic" losses was proposed. It was confirmed that the intrinsic losses were smaller than the corresponding extrinsic losses. The intrinsic piezoelectric loss existed in both soft and hard PZTs; ,50% of the loss of piezoelectric d -constant was derived from the elastic and dielectric losses. The most notable difference between the soft and hard PZTs was observed in their elastic losses. [source]

Use of Titanates to Achieve a Temperature-Stable Low-Temperature Cofired Ceramic Dielectric for Wireless Applications

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2002
Steve Xunhu Dai
A low-loss and near-zero temperature coefficient of resonant frequency (Tf) low-temperature cofired ceramic (LTCC) host dielectric was developed for portable consumer wireless device applications. The low Tf was realized by compensating the Al2O3 -filled-glass dielectric with admixtures of TiO2 (negative temperature coefficient of dielectric constant (T,)) in the starting formulation. XRD data indicated a portion of the TiO2 in the starting formulation dissolved into the glass, and extensive formation of crystalline titanium compounds was observed via a nucleation and growth mechanism. The dissolution of TiO2 in the glass and subsequent formation of titanium compounds was believed to result in the relatively small amount of TiO2 required to achieve a near-zero Tf in the final sintered structure. [source]

Molecular Dynamics of Podand Studied by Broadband Dielectric and Nuclear Magnetic Resonance Spectroscopies,,

MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 19-20 2007
Bakyt Orozbaev
Abstract Nuclear magnetic resonance (NMR) and broadband dielectric spectroscopies (BDS) were used to analyze the molecular dynamics in P10.3H Podand. The temperature studies of NMR line and magnetic spin,lattice relaxation times accompanied by DS investigation enabled us to distinguish three main dynamical processes connected with the motions of the P10.3H Podand chains. In the low-temperature region the magnetic relaxation was associated with fast axial C3 rotation of methyl groups. Moreover, two other independent processes were observed and interpreted as (i) segmental motion of both oxyethylene and ethylene units, and (ii) the overall motion involved in the melting process. [source]

Dielectric in situ sensor monitoring of phase separation and changes in the state of each phase

MACROMOLECULAR SYMPOSIA, Issue 1 2003
D. Kranbuehl
Abstract Frequency dependent dielectric measurements have been used to monitor and characterize the phase separation process and changes in state of each phase. The measurements are made in situ using a micro planar sensor. They can be made both in the laboratory as well as in an industrial production or use environment. Two examples are presented. The first is monitoring the onset of phase separation, the buildup in Tg and change in composition of each phase during "reactive processing" of a high performance thermoplastic (TP) PPI, thermoset precursors (TS) DGEBA-MCDEA intially homogeneous blend. The second example involves monitoring the stability, onset of phase separation, as a function of temperature on a mineral oil, stearyl alcohol, water, sufactant emulsion used in the cosmetic industry. [source]

Dielectric and magnetic properties of citrate-route-processed Li,Co spinel ferrites

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 7 2007
Nutan Gupta
Abstract Cobalt-substituted lithium ferrites (with general composition Li0.5,x /2CoxFe2.5,x /2O4, where x = 0.0, 0.2, 0.4, 0.5 and 0.6) were prepared at lower processing temperatures (,600 °C) by the citrate route. The single-phase spinel structure was confirmed by X-ray diffraction. The average particle size of calcined powders calculated by the Scherrer formula is estimated to be 8,90 nm, whereas an average particle size of ,20 nm is observed from TEM for Co concentration x = 0.5. Average grain sizes from SEM micrographs of pellets sintered at 1000 °C (1 h) are observed to be 0.5,1 ,m, much smaller than the size reported for the standard ceramic method (2.1,6.8 ,m). The experimental density is observed to be 3.59,4.47 gm/cm3, which is greater than 85% of the densities evaluated from XRD. Compared with the standard ceramic method, lower dielectric constant (10,103) and higher dc resistivity (105,1010 , cm) is observed for Li,Co ferrites prepared by the citrate route. Improved magnetic properties, such as higher saturation magnetization (38,79 emu g,1) and Curie temperature (535 to 620 °C) are also investigated for the citrate-route-processed samples. These results demonstrate promising features of Li,Co ferrites in microwave applications. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Dielectric and calorimetric studies of ferroelectric phase transitions in Li(2,x)NaxGe4O9 crystals

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 15 2005
I. Cebula
Abstract The ferroelectric phase transitions of LiNaGe4O9, Li1.1Na0.9Ge4O9, Li1.2Na0.8Ge4O9 and Li1.7Na0.3Ge4O9 crystals were studied. Experiments were carried out by means of classical dielectric measurements and using an AC calorimetric specific-heat measuring system. Critical behaviour is explained within Landau theory. The expansion coefficients of the state equation are determined. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Dielectric and optical studies of phase transitions in [(CH3)2NH2]5Cd2CuCl11 crystal

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 12 2004
Yu. Elyashevskyy
Abstract Single crystals of [(CH3)2 NH2]5Cd2CuCl11 have been grown and their dielectric and optical properties have been studied. Electric permittivity, losses and linear optic birefringence measurements have shown that the obtained new crystal is isomorphous with the original one , [(CH3)2 NH2]5Cd3Cl11. Phase transitions were observed at 175 K (continuous) and 120 K (first order). It means that partial replacing of cadmium atoms by copper ones does not change the structure and the heavy Cd2CuCl11,2 anions do not influence significantly the interaction of dimethylammonium cations. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Hopping parameters in densely packed submicron crystallites

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2008
L. J. Huijbregts
Abstract The density of states g (E) in the hopping process in closely packed crystallites is expected to differ from g (E) within a single crystallite [Zhang and Shklovskii, Phys. Rev. B 70, 115317 (2004)]. Dielectric scans are well suited to quantify these differences. Here we illustrate the method by discussing the results on Phthalcon-11, a cobalt phthalocyanine with submicron dimensions. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

ChemInform Abstract: Ab initio Study of Structural, Dielectric, and Dynamical Properties of Zinc-Blende ZnX (X: O, S, Se, Te).

CHEMINFORM, Issue 21 2009
You Yu
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [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 2010
Mater.
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 Treatment

ADVANCED FUNCTIONAL MATERIALS, Issue 16 2010
Jaeyoung 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 Limit

ADVANCED FUNCTIONAL MATERIALS, Issue 4 2010
Limin 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]

Enhancement of Carrier Mobilities of Organic Semiconductors on Sol,Gel Dielectrics: Investigations of Molecular Organization and Interfacial Chemistry Effects

ADVANCED FUNCTIONAL MATERIALS, Issue 3 2009
Tommy Cahyadi
Abstract The dielectric-semiconductor interfacial interactions critically influence the morphology and molecular ordering of the organic semiconductor molecules, and hence have a profound influence on mobility, threshold voltage, and other vital device characteristics of organic field-effect transistors. In this study, p-channel small molecule/polymer (evaporated pentacene and spin-coated poly(3,3,;-didodecylquarterthiophene) , PQT) and n-channel fullerene derivative ({6}-1-(3-(2-thienylethoxycarbonyl)-propyl)-{5}-1-phenyl-[5,6]-C61 , TEPP-C61) show a significant enhancement in device mobilities ranging from ,6 to ,45 times higher for all classes of semiconductors deposited on sol,gel silica gate-dielectric than on pristine/octyltrichlorosilane (OTS)-treated thermally grown silica. Atomic force microscopy, synchrotron X-ray diffraction, photoluminescence/absorption, and Raman spectroscopy studies provide comprehensive evidences that sol,gel silica dielectrics-induced enhancement in both p- and n-channel organic semiconductors is attributable to better molecular ordering/packing, and hence reduced charge trapping centers due to lesser structural defects at the dielectric-semiconductor interface. [source]

Defect Tolerance and Nanomechanics in Transistors that Use Semiconductor Nanomaterials and Ultrathin Dielectrics,

ADVANCED FUNCTIONAL MATERIALS, Issue 17 2008
Jong-Hyun Ahn
Abstract This paper describes experimental and theoretical studies of the mechanics of free-standing nanoribbons and membranes of single-crystalline silicon transfer printed onto patterned dielectric layers. The results show that analytical descriptions of the mechanics agree well with experimental data, and they explicitly reveal how the geometry of dielectric layers (i.e., the width and depth of the features of relief) and the silicon (i.e., the thickness and widths of the ribbons) affect mechanical bowing (i.e., "sagging") in the suspended regions of the silicon. This system is of practical importance in the use of semiconductor nanomaterials for electronic devices, because incomplete sagging near defects in gate dielectrics provides a level of robustness against electrical shorting in those regions which exceeds that associated with conventional deposition techniques for thin films. Field effect transistors formed using silicon nanoribbons transferred onto a range of ultrathin gate dielectrics, including patterned epoxy, organic self-assembled monolayers, and HfO2, demonstrate these concepts. [source]

Organic Thin Film Transistors with Polymer Brush Gate Dielectrics Synthesized by Atom Transfer Radical Polymerization

ADVANCED FUNCTIONAL MATERIALS, Issue 1 2008
C. 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 2007
S. 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 Dielectrics

ADVANCED MATERIALS, Issue 21 2009
Yu 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 2006
K. 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]

Highly Bendable, Transparent Thin-Film Transistors That Use Carbon-Nanotube-Based Conductors and Semiconductors with Elastomeric Dielectrics,

ADVANCED MATERIALS, Issue 3 2006
Q. Cao
Transparent flexible thin-film transistors (see Figure) have been made using single-walled carbon nanotube networks of high and moderate coverages as the conducting and semiconducting layers. Electrical (e.g., good performance on plastic), optical (e.g. transparency to visible wavelengths), and mechanical (e.g. extreme flexibility) characteristics that would be difficult, or impossible, to achieve with conventional materials are reported. [source]