Showing papers on "Field effect published in 2006"

Ionic amorphous oxide semiconductors: Material design, carrier transport, and device application

Abstract: Recently we have reported the room temperature fabrication of transparent and flexible thin film transistors on a polyethylene terephthalate (PET) film substrate using an ionic amorphous oxide semiconductor (IAOS) in an In2O3–ZnO–Ga2O3 system. These transistors exhibit a field effect mobility of ∼10 cm2 (V s)−1, which is higher by an order of magnitude than those of hydrogenated amorphous Si and pentacene transistors. This article describes a chemical design concept of IAOS, and its unique electron transport properties, and electronic structure, by comparing them with those of conventional amorphous semiconductors. High potential of IAOS for flexible electronics is addressed.

Nanostructure Dependence of Field-Effect Mobility in Regioregular Poly(3-hexylthiophene) Thin Film Field Effect Transistors

Abstract: Low polydispersity regioregular polythiophenes with number average molecular weights ranging from 2 to 13 kDa were cast under the same conditions from solution to form a series of field effect transistors (FETs). Tapping mode AFM and grazing incidence small-angle X-ray scattering revealed that in all cases the polymers formed regular nanofibrillar morphologies with the width of nanofibrils proportional to the weight average contour length of polymer chains, indicating that conjugated backbones were oriented perpendicular to the nanofibril axes. FET charge carrier mobilities exhibited exponential dependence on nanofibril width, pointing to the decisive role of extended conjugated pathways in charge transport.

Inorganic nanotubes: a novel platform for nanofluidics.

Abstract: Templating approaches are being developed for the synthesis of inorganic nanotubes, a novel platform for nanofluidics. Single crystalline semiconductor GaN nanotubes have been synthesized using an epitaxial casting method. The partial thermal oxidation of silicon nanowires leads to the synthesis of silica nanotubes. The dimension of these nanotubes can be precisely controlled during the templating process. These inorganic nanotubes can be integrated into metal-oxide solution field effect transistors (MOSolFETs), which exhibit rapid field effect modulation of ionic conductance. These nanofluidic devices have been further demonstrated to be useful for single-molecule sensing, as single DNA molecules can be readily detected either by charge effect or by geometry effect. These inorganic nanotubes will have great implications in subfemtoliter analytical technology and large-scale nanofluidic integration.

High-performance ZnO nanowire field effect transistors

Abstract: ZnO nanowires with high crystalline and optical properties are characterized, showing strong effect of the surface defect states. In order to optimize the performance of devices based on these nanowires, a series of complementary metal-oxide semiconductor compatible surface passivation procedures is employed. Electrical transport measurements demonstrate significantly reduced subthreshold swing, high on/off ratio, and unprecedented field effect mobility.

Anisotropic field effect mobility in single crystal pentacene

Abstract: Fan-shaped electrodes were designed on Si∕SiO2 substrate to measure the anisotropic field effect mobility in freestanding single crystal pentacene. Field effect transistor was fabricated by placing single crystal pentacene on the prepatterned electrodes. The contact between the electrodes and single crystal pentacene was enhanced by applying pressure. Angle dependence of field effect mobility in single crystal pentacene showed remarkably anisotropic behavior. The highest mobility value was estimated to be ∼2.3cm2∕Vs at room temperature.

High-mobility amorphous In2O3–10wt%ZnO thin film transistors

Abstract: The authors report on the fabrication and characterization of thin film transistors that use sputter deposited amorphous indium zinc oxide both for the channel and source-drain metallizations in a gate-down configuration. The channel and source-drain layers were deposited from a single In2O3–10wt%ZnO ceramic target using dc magnetron sputtering onto an unheated substrate. The carrier densities in the channel (2.1×1017∕cm3) and source/drain regions (3.3×1020∕cm3) were adjusted by changing the reactive oxygen content in the sputter chamber during deposition. The resulting transistors operate as depletion mode n-channel field effect devices with saturation mobility of 20cm2∕Vs and on/off current ratio of 108.

High carrier density and metallic conductivity in poly(3- hexylthiophene) achieved by electrostatic charge injection

Abstract: The use of electrostatic charge injection (i.e., the transverse field effect) to induce both very large two-dimensional hole densities (∼ 1015 charges cm–2) and metallic conductivities in poly(3-hexylthiophene) (P3HT) is reported. Films of P3HT are electrostatically gated by a solution-deposited polymer-electrolyte gate dielectric in a field-effect-transistor configuration. Exceptionally high hole field-effect mobilities (up to 0.7 cm2 V–1 s–1) are measured concurrently with large hole densities, resulting in an extremely large sheet conductance of 200 μS sq.–1. The large room-temperature conductivity of 1000 S cm–1 together with the very low measured activation energies (0.7–4 meV) suggest that the metal–insulator transition in P3HT is achieved. A maximum in sheet conductance versus charge density is also observed, which may result from near-filling of the valence band or from charge correlations that lower the carrier mobility. Importantly, the large hole densities in P3HT are achieved using capacitive coupling between the polymer-electrolyte gate dielectric and P3HT (i.e., the field effect) and not via chemical or electrochemical doping. Electrostatic control of carrier density up to 1015 charges cm–2 (∼ 1022 charges cm–3) opens opportunities to explore systematically the importance of charge-correlation effects on transport in conjugated polymers without the structural rearrangement associated with chemical or electrochemical doping.

High performance ZnO nanowire field effect transistor using self-aligned nanogap gate electrodes

Abstract: A field effect transistor (FET) using a zinc oxide nanowire with significantly enhanced performance is demonstrated. The device consists of single nanowire and self-aligned gate electrodes with well defined nanosize gaps separating them from the suspended nanowire. The fabricated FET exhibits excellent performance with a transconductance of 3.06μS, a field effect mobility of 928cm2∕Vs, and an on/off current ratio of 106. The electrical characteristics are the best obtained to date for a ZnO transistor. The FET has a n-type channel and operates in enhancement mode. The results are close to those reported previously for p-type carbon nanotube (CNT) FETs. This raises the possibility of using ZnO as the n-type FET with a CNT as the p-type FET in nanoscale complementary logic circuits.

Organic metal electrodes for controlled p- and n-type carrier injections in organic field-effect transistors

Abstract: Fine control of p-, n-, and ambipolar-type field-effect transistor (FET) operations is successfully demonstrated in prototypical single-crystal organic FETs with use of chemically tunable nature of Fermi energy in tetrathiafulvalene-tetracyanoguinodimethane-based organic metal electrodes. Carrier-type preference and rectifying nature in the organic-organic contacts are revealed in terms of the FET operations as well as of the all-organic Schottky diode characteristics.

Local switching of two-dimensional superconductivity using the ferroelectric field effect.

Abstract: Correlated oxides display a variety of extraordinary physical properties including high-temperature superconductivity and colossal magnetoresistance. In these materials, strong electronic correlations often lead to competing ground states that are sensitive to many parameters--in particular the doping level--so that complex phase diagrams are observed. A flexible way to explore the role of doping is to tune the electron or hole concentration with electric fields, as is done in standard semiconductor field effect transistors. Here we demonstrate a model oxide system based on high-quality heterostructures in which the ferroelectric field effect approach can be studied. We use a single-crystal film of the perovskite superconductor Nb-doped SrTiO3 as the superconducting channel and ferroelectric Pb(Zr,Ti)O3 as the gate oxide. Atomic force microscopy is used to locally reverse the ferroelectric polarization, thus inducing large resistivity and carrier modulations, resulting in a clear shift in the superconducting critical temperature. Field-induced switching from the normal state to the (zero resistance) superconducting state was achieved at a well-defined temperature. This unique system could lead to a field of research in which devices are realized by locally defining in the same material superconducting and normal regions with 'perfect' interfaces, the interface being purely electronic. Using this approach, one could potentially design one-dimensional superconducting wires, superconducting rings and junctions, superconducting quantum interference devices (SQUIDs) or arrays of pinning centres.

Field-effect mobility temperature modeling of 4H-SiC metal-oxide-semiconductor transistors

Abstract: Here a physically based channel mobility model has been developed to investigate the temperature dependence of the field-effect mobility of 4H-SiC metal-oxide-semiconductor (MOS) transistors with thermally oxidized gate insulators. This model has been designed so that it accounts for the high density of traps at the MOS interface. This temperature dependence is a key issue for silicon carbide electronics, as its basic material properties make it the foremost semiconductor for high power/high temperature electronic devices in applications such as spacecraft, aircraft, automobile, and energy distribution. Our modeling suggests that the high density of charged acceptor interface traps, encountered in thermally grown gate oxides, modulates the channel mobility due to the Coulomb scattering of free carriers in the inversion layer. When the temperature increases, the field-effect mobility of these devices also increases, due to an increase in inversion charge and a reduction of the trapped charge. Experimental ...

Comparison of organic diode structures regarding high-frequency rectification behavior in radio-frequency identification tags

Abstract: In this article, we compare the direct current (dc) and high-frequency performance of two different organic diode structures, a vertical diode and an organic field effect transistor (OTFT) with shorted drain-gate contact, regarding their application in a rectifying circuit. For this purpose, we fabricated both diode structures using the organic semiconductor pentacene. dc measurements were performed showing a space-charge-limited current mobility of more than 0.1cm2∕Vs for the vertical diode and a field effect mobility of 0.8cm2∕Vs for the OTFT with shorted source-drain. High-frequency measurements of those diode structures in a rectifier configuration show that both types of diodes are able to follow the base-carrier frequency of 13.56MHz which is essential for viable radio-frequency-identification (rf-ID) tags. Based on those results we evaluate the performance limits and advantages of each diode configuration regarding their application in an organic rf-ID tag.

Directional flow induced by synchronized longitudinal and zeta-potential controlling AC-electrical fields

Abstract: Electroosmotic flow (EOF) in a microchannel can be controlled by electronic control of the surface charge using an electrode embedded in the wall of the channel. By setting a voltage to the electrode, the zeta-potential at the wall can be changed locally. Thus, the electrode acts as a "gate" for liquid flow, in analogy with a gate in a field-effect transistor. In this paper we will show three aspects of a Field Effect Flow Control (FEFC) structure. We demonstrate the induction of directional flow by the synchronized switching of the gate potential with the channel axial potential. The advantage of this procedure is that potential gas formation by electrolysis at the electrodes that provide the axial electric field is suppressed at sufficiently large switching frequencies, while the direction and magnitude of the EOF can be maintained. Furthermore we will give an analysis of the time constants involved in the charging of the insulator, and thus the switching of the zeta potential, in order to predict the maximum operating frequency. For this purpose an equivalent electrical circuit is presented and analyzed. It is shown that in order to accurately describe the charging dynamics and pH dependency the traditionally used three capacitor model should be expanded with an element describing the buffer capacitance of the silica wall surface.

ZnO thin-film transistors with polycrystalline (Ba,Sr)TiO3 gate insulators

Abstract: The electrical characteristics of ZnO thin-film transistors with high-k (Ba,Sr)TiO3 gate dielectrics are presented. The ZnO and (Ba,Sr)TiO3 thin films were deposited on Pt, exhibiting polycrystalline characteristics. The thin-film devices demonstrated transistor behavior over the range of 0–10V with a stable threshold voltage of approximately 1.2V. The field effect mobility, subthreshold slope, and on/off ratio were measured to be 2.3cm2V−1s−1, 0.25V∕decade, and 1.5×108, respectively. The measured transistor performance characteristics suggest that ZnO∕(Ba,Sr)TiO3 structures are well suited for both polycrystalline thin-film transistors for display applications and future higher performance transistors based on single crystal ZnO.

Large Photoresponsivity in High‐Mobility Single‐Crystal Organic Field‐Effect Phototransistors

Abstract: A strong interest in organic devices has emerged recently due to their potential in large-area and low-cost electronics. However, the effects of light on the electrical performance of organic field-effect transistors (OFETs) has been hardly explored and mainly focused only on polymer-based devices. The preparation of OFETs exhibiting photoresponsivity, which could act as light sensors, photoswitches or optoelectronic memory elements, opens new avenues of research into promising device applications. Very recently, we reported on a new generation of materials for OFETs, which consists of low-molecularweight molecules based on tetrathiafulvalene (TTF) derivatives. These materials were processed from solution and revealed very high mobility; these are two desirable conditions that have often been considered conflicting. The highest mobility was found for single crystals of dithiophene-tetrathiafulvalene (DT-TTF, mmax=1.4 cm V 1 s ) and dibenzo-tetrathiafulvalene (DB-TTF, mmax=1 cm V 1 s ) (Figure 1a). Here, we demonstrate that these crystals combine high OFET performance with a large photoresponsivity and can thus operate as phototransistors, that is, light can be used as an additional parameter to control the number of mobile charges. The synthesis of the molecules was carried out as previously described. Their UV/Vis spectra in the solid state showed a maximum wavelength absorption peak at 450 and 476 nm for DT-TTF and DB-TTF, respectively. The optical band gaps were then estimated from the absorption edges of the spectra and were found to be very similar, with values of 2.51 eV for DTTTF and 2.36 eV for DB-TTF. These energy values indicate the facility to induce a transition between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO); that is, the lower the optical band gap is, the easier it will be to promote electrons from the HOMO to the LUMO by absorption of photons. Such electron transitions will then generate holes and electrons which will contribute to the resulting transport properties. The phototransistor device configuration used is shown in Figure 1b. To study the effect of light, a white-light lamp with energy of 2.5 Wcm 2 was employed. Figure 2 displays the

Directly deposited nanocrystalline silicon thin-film transistors with ultra high mobilities

Abstract: The authors report ultrahigh mobility nanocrystalline silicon thin-film transistors directly deposited by radio-frequency plasma enhanced chemical vapor deposition at 150°C. The transistors show maximum effective field effect mobilities of 450cm2∕Vs for electrons and 100cm2∕Vs for holes at room temperature. The authors argue that the key factor in their results is the reduction of the oxygen content, which acts as an accidental donor.

Acridine orange base as a dopant for n doping of C60 thin films

Abstract: We present a study on n doping of C60 thin films by acridine orange base [3,6-bis(dimethylamino)acridine(AOB)] combining conductivity, field effect, and Seebeck measurements. An increase of more than six orders of magnitude in conductivity is observed for a doping ratio of 6mol%, accompanied by a decrease in the activation energy from 0.64to0.15eV compared to the undoped C60. We observe a clear doping effect immediately after sample preparation, but also a further activation by annealing or illumination. The field effect and Seebeck measurements confirm n-type conduction of C60 thin films and show that deep donor states are formed in AOB-doped C60 thin films. A field effect mobility of 0.2cm2∕Vs is achieved for a doping level of 1.8mol%. Near Infrared (NIR) and Fourier transform infrared (FTIR) spectra demonstrate electron transfer from the dopant to the matrix: For C60 doped with AOB, C60− is present in NIR absorption and FTIR spectra. On the other hand, a peak corresponding to acridine orange [3,6-bis(d...

Field effect luminescence from Si nanocrystals obtained by plasma-enhanced chemical vapor deposition

Abstract: Field effect induced luminescence has been achieved by alternate tunnel injection of electrons and holes into Si nanocrystals. The emitting device is a metal-oxide-semiconductor structure with a semitransparent polycrystalline Si contact ∼250nm thick and a silicon-rich silicon oxide layer of about 40nm deposited on a p-type Si substrate by plasma-enhanced chemical vapor deposition. The electroluminescence is optimized for a Si excess of 17% and annealing at 1250°C for 1h in nitrogen-rich atmosphere. The pulsed emission presents typical decay times of ∼5μs and external quantum efficiencies of ∼0.03%.

Field Effect Diode (FED): A novel device for ESD protection in deep sub-micron SOI technologies

Abstract: In this paper the authors present the field effect diode (FED) as a novel device with a new approach for ESD protection in SOI. Device parameters are identified and optimized to achieve optimum ON and OFF behavior. Furthermore, the authors present two ways the FED can be used in an ESD protection scheme: in I/O clamping and in a high-voltage supply clamp

Detection sensitivity of genetic field effect transistor combined with charged nanoparticle-DNA conjugate

Abstract: We demonstrated the effectiveness of introduction of charged nanoparticle-DNA conjugate for detection sensitivity of the genetic field effect transistor (FET), of which the principle is based on the potentiometric detection of charge density change on the gate surface. The large amount of negative charges on the gate insulator induced strongly the electrostatic interaction with electrons in silicon crystal by field effect resulting in the bigger shift of threshold voltage. The genetic FET platform combined with the charged nanoparticle-DNA conjugate is suitable for a simple, sensitive, accurate and inexpensive system for DNA analyses in clinical diagnostics.

4.1: Distinguished Paper: High Mobility Top-Gate Zinc Oxide Thin-Film Transistors (ZnO-TFTs) for Active-Matrix Liquid Crystal Displays

Abstract: High-performance top-gate ZnO thin-film transistors (TFTs) for AM-LCDs have been developed. Sputtered ZnO was used as an active channel and silicon nitride (SiNx) deposited by plasma enhanced chemical vapor deposition (P-CVD) was used as a gate insulator. Field effect mobility and threshold voltage of the ZnO-TFT are 50.3 cm2/V⋅sec and 1.1 V, respectively. We first demonstrated a 1.46″ diagonal AM-LCD driven by ZnO-TFTs.

Aging effects in pentacene thin-film transistors: Analysis of the density of states modification

Abstract: Field effect analysis has been employed in order to calculate the density of states of high quality pentacene thin-film transistors. The degradation of the electrical characteristics caused by the exposure to air has been studied and discussed in term of density of states modification. The calculated density of the states has been approximated by two exponential terms, as in amorphous silicon, and it has been used in a two-dimensional numerical simulation in order to reproduce the electrical characteristic variation with respect of the temperature and aging time.

Highly Stable Ga2O3-In2O3-ZnO TFT for Active-Matrix Organic Light-Emitting Diode Display Application

Abstract: We, for the first time, have successfully fabricated amorphous Ga 2O3-In2O3-ZnO thin film transistor (TFT) with excellent electrical properties and good stability under constant current stress. This transistor shows a field effect mobility of 10 cm2/Vs, an off current below 2 pA and a drain current on-to-off ratio of above 108. The threshold voltage shift was less than 0.2 V for 100 hours at 3 muA and 60 degC. Such stable oxide transistors can be utilized as driving transistor for large area OLED display

Built-in field effect on the electron mobility in AlN∕GaN∕AlN quantum wells

Abstract: The authors demonstrated theoretically that compensation of the built-in electric field in AlN∕GaN∕AlN heterostructures with the externally applied perpendicular electric field may lead to the increase of the in-plane electron drift mobility. It has been shown that two- to fourfold increase of the room temperature mobility can be achieved for both nondegenerate and degenerate electron densities. Their calculations clarified the role of the intersubband electron transitions mediated by optical phonons in limiting the carrier mobility in GaN-based heterostructures. The tuning of the electron mobility with the perpendicular electric field may impact design of the high-power GaN∕AlGaN heterostructure field-effect transistors.

Field-effect modulation of the transport properties of nondoped SrTiO3

Abstract: We have fabricated SrTiO3 (100) single crystal field-effect transistors with amorphous and epitaxial CaHfO3 gate insulator layers. The devices with amorphous insulator layers showed nearly temperature independent behavior. The transistors with epitaxial interfaces exhibited a large improvement over the amorphous devices. The field-effect mobility was found to increase at low temperature, reaching 35cm2∕Vs at 50K. This result shows that the carriers accumulated by the field effect on the SrTiO3 side of the gate interface behaved as would be expected for electron-doped SrTiO3. An insulator-metal transition, induced by field-effect doping, was observed in epitaxial SrTiO3-based transistors.

Complementary organic field effect transistors by ultraviolet dielectric interface modification

Abstract: The realization of p- and n-type pentacene organic field effect transistors and an organic inverter stage is reported based on selective ultraviolet (UV) modification of the polymer dielectric in air. Apart from the UV radiation treatment, the device structures are identical. The achieved field effect carrier mobilities for both transistor types are ≈0.1cm2∕Vs. Similar performance data for both transistor types as well as an observed low current hysteresis qualify the UV treatment for organic complementary metal oxide semiconductor (O-CMOS) technology. The realized O-CMOS inverter exhibits stable operation below its supply voltage, as well as a gain of 17.

Controlling field-effect mobility in pentacene-based transistors by supersonic molecular-beam deposition

Abstract: We show that pentacene field-effect transistors, fabricated by supersonic molecular beams, have a performance strongly depending on the precursor’s kinetic energy (KE). The major role played by KE is in achieving highly ordered and flat films. In the range KE≈3.5–6.5eV, the organic field effect transistor linear mobility increases of a factor ∼5. The highest value (1.0cm2V−1s−1) corresponds to very uniform and flat films (layer-by-layer type growth). The temperature dependence of mobility for films grown at KE>6eV recalls that of single crystals (bandlike) and shows an opposite trend for films grown at KE⩽5.5eV.