Showing papers on "Field effect published in 2019"

MoTe2 Lateral Homojunction Field-Effect Transistors Fabricated using Flux-Controlled Phase Engineering.

Abstract: The coexistence of metallic and semiconducting polymorphs in transition-metal dichalcogenides (TMDCs) can be utilized to solve the large contact resistance issue in TMDC-based field effect transist...

Measurements of electrically tunable refractive index of MoS2 monolayer and its usage in optical modulators

Abstract: Two-dimensional materials hold a great promise for developing extremely fast, compact and inexpensive optoelectronic devices. A molybdenum disulphide (MoS2) monolayer is an important example which shows strong, stable and gate tunable optical response even at room temperature near excitonic transitions. However, optical properties of a MoS2monolayer are not documented well. Here, we investigate the electric field effect on optical properties of a MoS2 monolayer and extract the dependence of MoS2 optical constants on gating voltage. The field effect is utilised to achieve ~10% visible light modulation for a hybrid electro-optical waveguide modulator based on MoS2. A suggested hybrid nanostructure consists of a CMOS compatible Si3N4 dielectric waveguide sandwiched between a thin gold film and a MoS2 monolayer which enables a selective enhancement of polarised electro-absorption in a narrow window of angles of incidence and a narrow wavelength range near MoS2 exciton binding energies. The possibility to modulate visible light with 2D materials and the robust nature of light modulation by MoS2 could be useful for creation of reliable ultra-compact electro-optical hybrid visible-light modulators.

Gate-Tunable Near-Field Heat Transfer

Abstract: Active control over the flow of heat in the near-field holds promise for nanoscale thermal management, with applications in refrigeration, thermophotovoltaics, and thermal circuitry. Analogously to its electronic counterpart, the metal–oxide–semiconductor (MOS) capacitor, we propose a thermal switching mechanism based on accumulation and depletion of charge carriers in an ultrathin plasmonic film, via application of external bias. In our proposed configuration, the plasmonic film is placed on top of a polaritonic dielectric material that provides a surface phonon polariton (SPhP) thermal channel, while also ensuring electrical insulation for application of large electric fields. The variation of carrier density in the plasmonic film enables the control of the surface plasmon polariton (SPP) thermal channel. We show that the interaction of the SPP with the SPhP significantly enhances the net heat transfer. We study SiC as the oxide and explore three classes of gate-tunable plasmonic materials, transparent ...

Magnetotransport Experiments on Fully Metallic Superconducting Dayem-Bridge Field-Effect Transistors

Abstract: The field effect, as in a field-effect transistor (FET), allows control of the switching current in a metallic superconductor, without affecting the critical temperature or normal-state resistance. Here magnetotransport experiments on Ti-based superconducting FETs reveal several physical insights: The phenomenon occurs at the sample surface, the field effect causes a transition from ballistic to tunnel-like behavior, and a mixed superconducting--normal-metal state is possible at high gate voltages. Such a device could be the cornerstone of easily fabricated monolithic architectures for classical or quantum computing, and a host of other applications in (opto)electronics.

Solution-Processed Organic Field-Effect Transistors with High Performance and Stability on Paper Substrates.

Abstract: High-performance operationally stable organic field-effect transistors were successfully fabricated on a PowerCoat HD 230 paper substrate with a TIPS-pentacene:polystyrene blend as the active layer and poly(4-vinylphenol)/HfO2 as the hybrid gate dielectric. The fabricated devices exhibited excellent p-channel characteristics with a maximum and av field effect mobility of 0.44 and 0.22(±0.11) cm2 V–1 s–1, respectively, av threshold voltage of 0.021(±0.63) V, and current on–off ratio of ∼105 while operating at −10 V. These devices exhibited remarkable stability under effects of gate bias stress and large number of repeated transfer scans with negligible performance spread. In addition, these devices displayed very stable electrical characteristics after long exposure periods to humidity and an excellent shelf life of more than 6 months in ambient environment. Thermal stress at high temperatures however deteriorates the device characteristics because of the generation and propagation of cracks in the active ...

EM Drive Thruster by Anti Maxwell Dual Monopole Tubular Interference Field Reduction Around a Conductor.

Abstract: A so called Em Drive ( Electro Magentic Drive) defy classical physics expectations because it shows repellent less or reaction less thruster qualities. According to Quantum FFF Theory (Function Follows Form at the quantum level) however, the magnetic field is build on two monopole rigid string particles which can be represented as curved lines of radiation trajectories, for a stable magnetic field more or less cooperating by opposing each other. Thus, the magnetic quantum field has always TWO different shaped curved monopole vector components: a North- and a South vector field component. This is comparable with the electric Quantum field, equipped with Plus and Minus vector components but it is in contrast with all other quantum fields like the neutrino- gravity-or x-gamma ray field. However, based on observation of iron filing-powder patterns, close to direct currents in a wire, it is postulated, that these monopole ( N+S) particle/ wave dualities travel locally parallel to each other inside the vacuum Axion/Higgs field, with a strong field reduction result also called a magnetic B-flied effect. A so called B field is well known to be present around a long solenoid. Inside the spiral solenoid, there is the strongest magnetic field present, however outside the solenoid the magnetic field is reduced down to zero, also originated by the anti Maxwell dipping field effect . This Anti Maxwell dipping phenomenon is originated by the interference of both ( N+S) monopole fields of parallel propagating magnetic monopole radiation trajectories, according to my monopole magnetic Quantum FFF model. These B field reductions (or dipping) are also observed to be concentrated in a tubular form around the current in a conductor..

Electronic Modulation of Near-Field Radiative Transfer in Graphene Field Effect Heterostructures.

Abstract: Manipulating heat flow in a controllable and reversible manner is a topic of fundamental and practical interest. Numerous approaches to perform thermal switching have been reported, but they typically suffer from various limitations, for instance requiring mechanical modulation of a submicron gap spacing or only operating in a narrow temperature window. Here, we report the experimental modulation of radiative heat flow by electronic gating of a graphene field effect heterostructure without any moving elements. We measure a maximum heat flux modulation of 4 ± 3% and an absolute modulation depth of 24 ± 7 mW m–2 V–1 in samples with vacuum gap distances ranging from 1 to 3 μm. The active area in the samples through which heat is transferred is ∼1 cm2, indicating the scalable nature of these structures. A clear experimental path exists to realize switching ratios as large as 100%, laying the foundation for electronic control of near-field thermal radiation using 2D materials.

Field Effect Modulation of Electrocatalytic Hydrogen Evolution at Back-Gated Two-Dimensional MoS2 Electrodes.

Abstract: Electrocatalytic activity for hydrogen evolution at monolayer MoS2 electrodes can be enhanced by the application of an electric field normal to the electrode plane. The electric field is produced b...

Field Effect and Photoconduction in Au25 Nanoclusters Films.

Abstract: Quantum-confined Au nanoclusters exhibit molecule-like properties, including atomic precision and discrete energy levels. The electrical conductivity of Au nanocluster films can vary by several orders of magnitude and is determined by the strength of the electronic coupling between the individual nanoclusters in the film. Similar to quantum-confined, semiconducting quantum dots, the electrical coupling in films is dependent on the size and structure of the Au core and the length and conjugation of the organic ligands surrounding it. Unlike quantum dots, however, semiconducting transport has not been reported in Au nanocluster films. Here, it is demonstrated that through a simple yet careful choice of cluster size and organic ligands, stable Au nanocluster films can electronically couple and become semiconducting, exhibiting electric field effect and photoconductivity. The molecule-like nature of the Au nanoclusters is evidenced by a hopping transport mechanism reminiscent of doped, disordered organic semiconductor films. These results demonstrate the potential of metal nanoclusters as a solution-processed material for semiconducting devices.

Near-ideal subthreshold swing MoS2 back-gate transistors with an optimized ultrathin HfO2 dielectric layer.

Abstract: In this paper, a near-ideal subthreshold swing MoS2 back-gate transistor with an optimized ultrathin HfO2 dielectric layer is reported with detailed physical and electrical characteristics analyses. Ultrathin (10 nm) HfO2 films created by atomic-layer deposition (ALD) at a low temperature with rapid-thermal annealing (RTA) at different temperatures from 200 °C to 800 °C have a great effect on the electrical characteristics, such as the subthreshold swing (SS), on-to-off current (I ON/I OFF) ratio, etc, of the MoS2 devices. Physical examinations are performed, including x-ray diffraction, atomic force microscopy, and electrical experiments of metal-oxide-semiconductor capacitance-voltage. The results demonstrate a strong correlation between the HfO2 dielectric RTA temperature and the film characteristics, such as film density, crystallization degree, grain size and surface states, inducing a variation in the electrical parameters, such as the leakage, D it, equivalent oxide thickness, SS, and I ON, as well as I ON/I OFF of the MoS2 field effect transistors with the same channel materials and fabrication methods. With a balance between the crystallization degree and the surface state, the ultrathin (10 nm) HfO2 gate dielectric RTA at 500 °C is demonstrated to have the best performance with a field effect mobility of 40 cm2 V-1 s-1 and the lowest SS of 77.6 mV-1 decade, which are superior to those of the control samples at other temperatures. The excellent transistor results with an optimized industry-based HfO2 ALD and RTA process provide a promising approach for MoS2 applications into the scaling of the nanoscale CMOS process.

HfO 2 -passivated black phosphorus field effect transistor with long-termed stability and enhanced current on/off ratio

Abstract: Enhanced on/off ratio, obvious threshold voltage left shift, newly emerging bipolar field effect performance and most importantly, excellent stability in ambient condition have been reported for the HfO2-passivated black phosphorus field effect transistors . Both Raman spectra and x-ray photoelectron spectroscopy (XPS) show a thickness reduction effect after HfO2 passivation, XPS further demonstrates that the formation of P-Hf and P-O chemical bonds contributes to the thinning of layered black phosphorus (BP), in which P-Hf bonds also provide chemical protection for BP flakes from degradation. Atomic force microscopy measures the thickness of the passivation layer and also verifies the stability of the passivated BP flakes.

Advantages of a buried-gate structure for graphene field-effect transistor

Abstract: Graphene field effect transistors (GFETs) with top-gate and back-gate structures have been extensively used without much consideration for compatibility with graphene. A comparative study of the electrical characteristics of buried-gate GFETs and top-gate GFETs revealed that the performance of buried-gate GFETs is drastically enhanced by having a better gate controllability, achieving three times higher field effect mobility (~3000 cmlsupg2l/supg/Vs) than top-gate GFETs with on/off ratio ~10.Carrier scattering was also substantially improved by minimizing the fringing field effect, which is found to be the origin of high series resistance in top-gate GFETs. Moreover, we showed by electromagnetic (EM) simulation that the electric field distribution inside the transistors is more uniform at the buried-gate GFETs than the top-gate GFETs.

New Approaches in Flexible Organic Field-Effect Transistors (FETs) Using InClPc

Abstract: Organic semiconductor materials have been the center of attention because they are scalable, low-cost for device fabrication, and they have good optical properties and mechanical flexibility, which encourages their research. Organic field-effect transistors (OFETs) have potential applications, specifically in flexible and low-cost electronics such as portable and wearable technologies. In this work we report the fabrication of an InClPc base flexible bottom-gate/top-contact OFET sandwich, configured by the high-evaporation vacuum technique. The gate substrate consisted of a bilayer poly(ethylene terephthalate) (PET) and indium-tin oxide (ITO) with nylon 11/Al2O3. The device was characterized by different techniques to determine chemical stability, absorbance, transmittance, bandgap, optical properties, and electrical characteristics in order to determine its structure and operational properties. IR spectroscopy verified that the thin films that integrated the device did not suffer degradation during the deposition process, and there were no impurities that affected the charge mobility in the OFET. Also, the InClPc semiconductor IR fingerprint was present on the deposited device. Surface analysis showed evidence of a nonhomogeneous film and also a cluster deposition process of the InClPc. Using the Tauc model, the device calculated indirect bandgap transitions of approximately 1.67 eV. The device's field effect mobility had a value of 36.2 cm2 V-1 s-1, which was superior to mobility values obtained for commonly manufactured OFETs and increased its potential to be used in flexible organic electronics. Also, a subthreshold swing of 80.64 mV/dec was achieved and was adequate for this kind of organic-based semiconductor device. Therefore, semiconductor functionality is maintained at different gate voltages and is transferred accurately to the film, which makes these flexible OFETs a good candidate for electronic applications.

Chirality Discrimination at the Single Molecule Level by Using a Cationic Supermolecule Quasi-Gated Organic Field Effect Transistor.

Abstract: Achieving rapid and highly sensitive small molecule chiral discrimination is a great challenge in modern-day analytical sciences. Herein, an organic field effect transistors (OFET) is developed by employing an imidazolium 3,5-dimethylphenylcabamoylated-β-cyclodextrin (Im+-Ph-β-CD) as both the recognition unit and a quasi gate, which induces a secondary accumulation channel of electrons in the n-type transistor to achieve the signal transduction and amplification via field effect. The charge of the imidazolium group is partially shielded due to its self-inclusion in the CD cavity, and this shielding effect is reduced at varying degrees in the existence of isomers due to the competitive inclusion. Consequently, the different weak intermolecular interactions related to the target-induced CD-enantiomer complexation with different geometry and stabilization energy for each isomer can be transformed to electronic signals based on the variety of Im+-Ph-β-CD's effective charge rather than the intrinsic charge of analytes, hence leading to chiral differentiation, and the hydrogen-bonding network of Im+-Ph-β-CD membrane further magnifies the signal. This working strategy even allows chiral discrimination of electrically neutral analytes. The as-prepared sensor affords rapid and real-time discrimination to small molecule enantiomers at single molecule level with a limit of detection of 8.1 × 10-19 M in a 200 μL volume (about 100 small molecules). Moreover, we prove the great potential of the chiral organic field effect transistor in quantitative analysis of commercial medicines.

Influence of free charge carrier density on the magnetic behavior of (Zn,Co)O thin film studied by Field Effect modulation of magnetotransport.

Abstract: The origin of (ferro)magnetic ordering in transition metal doped ZnO is a still open question. For applications it is fundamental to establish if it arises from magnetically ordered impurity clusters embedded into the semiconducting matrix or if it originates from ordering of magnetic ions dilute into the host lattice. In this latter case, a reciprocal effect of the magnetic exchange on the charge carriers is expected, offering many possibilities for spintronics applications. In this paper we report on the relationship between magnetic properties and free charge density investigated by using Zinc oxide based field effect transistors, in which the charge carrier density is modulated by more than 4 order of magnitude, from 1016 to 1020 e-/cm3. The magnetotransport properties are employed to probe the magnetic status of the channel both in pure and cobalt doped zinc oxide transistors. We find that it is widely possible to control the magnetic scattering rates by field effect. We believe that this finding is a consequence of the modulation of magnetization and carrier spin polarization by the electric field. The observed effects can be explained by the change in size of bound magnetic polarons that induces a percolation magnetic ordering in the sample.

Field-Effect Control of Metallic Superconducting Systems

Abstract: Despite metals are believed to be insensitive to field-effect and conventional Bardeen-Cooper-Schrieffer (BCS) theories predict the electric field to be ineffective on conventional superconductors, a number of gating experiments showed the possibility of modulating the conductivity of metallic thin films and the critical temperature of conventional superconductors. All these experimental features have been explained by simple charge accumulation/depletion. In 2018, electric field control of supercurrent in conventional metallic superconductors has been demonstrated in a range of electric fields where the induced variation of charge carrier concentration in metals is negligibly small. In fact, no changes of normal state resistance and superconducting critical temperature were reported. Here, we review the experimental results obtained in the realization of field-effect metallic superconducting devices exploiting this unexplained phenomenon. We will start by presenting the seminal results on superconducting BCS wires and nano-constriction Josephson junctions (Dayem bridges) made of different materials, such as titanium, aluminum and vanadium. Then, we show the mastering of the Josephson supercurrent in superconductor-normal metal-superconductor proximity transistors suggesting that the presence of induced superconducting correlations are enough to see this unconventional field-effect. Later, we present the control of the interference pattern in a superconducting quantum interference device indicating the coupling of the electric field with thesuperconducting phase. Among the possible applications of the presented phenomenology, we conclude this review by proposing some devices that may represent a breakthrough in superconducting quantum and classical computation.

Reduction of water-molecule-induced current-voltage hysteresis in graphene field effect transistor with semi-dry transfer using flexible supporter

Abstract: The polymethyl methacrylate-assisted wet transfer method of chemical vapor deposition (CVD) graphene has been widely used, thanks to its good coverage and simplicity. However, in the wet-transfer method, water molecules are inevitably trapped between the graphene and the substrate because the graphene is transferred to the substrate while floating in water. The trapped water molecules can cause the unwanted doping of graphene and hysteretic behavior in the current-voltage (I-V) curve. We here propose a new semidry transfer method using the Kapton tape as an additional flexible supporting layer. The N2 blowing and heating processes are added to vaporize the water molecules adsorbed on graphene layer right before the transfer step. By comparing the I-V characteristics of wet- and semidry-transferred graphene field effect transistor (GFET), the field effect mobility is found to be larger for the semidry-transferred GFET in comparison with the wet-transferred one, possibly due to the more uniform Coulomb potential landscape. Most importantly, the hysteretic behavior is found to be reduced in accordance with the decrease of the trapped water molecules. The averaged electron mobilities obtained from the GFET measurements are 1118 c m 2 / V s and 415 c m 2 / V s for semidry- and wet-transferred graphene, respectively. Our semidry transfer method can provide a simple and reliable way to transfer the CVD graphene onto an arbitrary substrate with the minimized number of trapped water molecules, which is readily applicable for large-scale substrates with potential of commercialization.

Acceptor Unit Effects for Ambipolar Organic Field-Effect Transistors Based on TIPS-Benzodithiophene Copolymers

Abstract: Two narrow band gap triisopropylsilyl substituted benzo[1,2-b:4,5-b] dithiophene (TIPS-BDT) derivatives, P1 (1.65 eV) and P2 (1.46 eV) are synthesized for ambipolar organic field-effect transistors and complementary inverters. Two electron acceptor units, heptadecanyl substituted thieno[3,4-c]pyrrole-4,6-dione (TPD) and ethylhexyl substituted diketopyrrolo[3,4-c]pyrrole (DPP) are incorporated to tune the structure and resulting properties of the donor-acceptor type copolymers. Structural modification based on the acceptor unit variation, resulted in comparable electrochemical, optical, microstructural, and charge transporting properties, as well as environmental and operational stability. TIPS-BDT copolymers with TPD acceptor units show comparatively superior performance, with field effect mobility ∼10-3 cm2V-1s-1 for both holes and electrons and inverter gain ∼18 with poly(methyl methacrylate) gate dielectric.

Remote Gating of Schottky Barrier for Transistors and Their Vertical Integration.

Abstract: This paper introduces a strategy to modulate a Schottky barrier formed at a graphene-semiconductor heterojunction. The modulation is performed by controlling the work function of graphene from a gate that is placed laterally away from the graphene-semiconductor junction, which we refer to as the remote gating of a Schottky barrier. The remote gating relies on the sensitive work function of graphene, whose local variation induced by locally applied field effect affects the change in the work function of the entire material. Using Kelvin probe force microscopy analysis, we directly visualize how this local variation in the work function propagates through graphene. These properties of graphene are exploited to assemble remote-gated vertical Schottky barrier transistors (v-SBTs) in an unconventional device architecture. Furthermore, a vertical complementary circuit is fabricated by simply stacking two remote-gated v-SBTs (pentacene layer as the p-channel and indium gallium zinc oxide layer as the n-channel) vertically. We consider that the remote gating of graphene and the associated device architecture presented herein facilitate the extendibility of graphene-based v-SBTs in the vertical assembly of logic circuits.