Field effect transistor Research Papers (original) (raw)

This paper presents a SPICE-like graphene field-effect transistor (GFET) model with an improved carrier mobility analysis. The model considers the mobility difference between the electrons and the holes in graphene, as well as the mobility variation against the carrier density. Closed-form analytical solutions have been derived, and the model has been implemented in Verilog-A language. This was compiled into an advanced design system. The proposed model gives excellent agreement between the simulation results and the measurement data for both the hole and electron conduction simultaneously. The model is suitable for the exploration of GFET-based applications, especially for those using the ambipolar transfer property of GFET.

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- Materials Science, Graphene, Transistor, Electrical And Electronic Engineering
- by Yang-kyu Choi
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- Physics, Mathematical Sciences, Physical sciences, Effective mass

We show that a ballistic quantum transport model based on the effective mass approximation can fairly well describe the I-V characteristics of armchair graphene nanoribbon FETs at all bias conditions, including regimes dominated by direct or band-to-band tunneling, provided first-order non-parabolic corrections be included in the simulation. This is achieved by means of an energy (position) dependent effective mass. The analysis is supported by comparisons with an atomistic tight-binding model.

- by E. Gnani
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- Chemistry, Nanoelectronics, Modeling, Silicon

Our electronic structure calculations were performed using the VASP code, 1 which implements the plane wave ultrasoft pseudopotential formalism based on density functional theory (DFT) within the local density approximation (LDA). The plane-wave cutoff was chosen as 286 eV. The quantum transport calculations were performed using the Atomistix ToolKit2.0 package, 2,3 which implements DFT-based real-space, nonequilibrium Green's function formalism. The mesh cutoff of carbon atom is chosen as 100 Ry to achieve the balance between calculation efficiency and accuracy. In the transport calculations, the gating effect is treated theoretically by adding an electrostatic potential equaling to gate voltage to the channel region of the device structure, so the effect of gate geometry is not considered. In all the calculations, the edges of GNRs are saturated with H to remove C dangling bonds. Structural optimizations were first carried out on some structures until atomic forces converged to 0.01 eV/Å. However, we found that the structural optimization does not change considerably the atomic or the electronic structures of GNRS. Thus, to save computational time, we have performed large-scale transport calculations with the fixed edge CC and C-H bond lengths at the optimized values of 1.409 Å and 1.10 Å, respectively.

- by Qimin Yan
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- Materials Science, Nanoelectronics, Electrochemistry, Carbon

The pressure sensitive ®eld effect transistor (PSFET) with insulated gate and its theoretical model developed by the authors are carefully discussed in this paper. The model explanation is preceded by short description of pressure sensor construction, fabricated in surface micromachining type technology. The pressure versus current characteristics of the model and comparison with measured output of real sensor are presented in this paper. Good convergence between simulated and measured sensor characteristics has been obtained in both theoretical and experimental sensor investigations. The observed differences are discussed in this paper. #

We have employed computer-aided furnace design and process simulation to optimize the conditions under which single-walled carbon nanotubes (SWCNTs) may be grown in high yields on 4 in. wafers for electronic device applications. Hydrokinetic simulations were performed to obtain optimized furnace structures and process conditions in terms of gas flow, temperature, and gas speed. Shower head structures and a flow isolation barrier were installed in an experimental 6 in. furnace, as suggested by the hydrokinetic simulations. To ensure clean surfaces and uniform catalyst islands, catalyst patterns were lifted off using Au films or polydimethylsiloxane. Photolithography was used to fabricate field-effect transistors with SWCNTs grown on 4 in. wafer substrates. The total yield of the nanotube devices increased from 30.5% to 96.4% after optimization.

- by king kong
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- Engineering, Materials Science, Design, Structure

Interest in dynamic behaviour of carriers in organic materials is motivated by possible applications that include organic thin film transistors, organic electroluminescent (EL) devices, and organic photo-conductors. It can also provide insight into modelling of carrier transport and trapping in organic semiconductors and insulators Here, we employ advanced SHG technique to probe and visualize real carrier motion in organic materials. This is a time-resolved microscopic optical SHG (TRM-SHG) technique that allows direct and selective probing of dynamic carrier motion in organic materials. TRM-SHG experiments using pentacene field effect transistors (FET) revealed dynamic changes of SHG intensity profiles arising from pentacene. Carrier velocity in organic solids is thus determined from the visualized carrier motion. We anticipate that this direct visualization technique will find wide application in the illustration of space charge field formation in organic and inorganic materials, including biomaterials and polymers.

- by Takaaki Manaka
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- Optics, Technology, Quantum Optics, Spectroscopy
- by David Humphreys
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- Physics, Analog Circuits, High Energy Physics, Data Acquisition System

ABSTRACT Silicon carbide (SiC) semiconductor devices for high power applications are now commercially available as discrete devices. Recently Schottky diodes are offered by both USA and Europe based companies. Active switching devices such as bipolar junction transistors (BJTs), field effect transistors (JFETs and MOSFETs) are now available on the commercial market. The interest is rapidly growing for these devices in high power and high temperature applications. The main advantages of wide bandgap semiconductors are their very high critical electric field capability. From a power device perspective the high critical field strength can be used to design switching devices with much lower losses than conventional silicon based devices both for on-state losses and reduced switching losses. This paper reviews the current state of the art in active switching device performance for both SiC and GaN. SiC material quality and epitaxy processes have greatly improved and degradation free 100 mm wafers are readily available. The SiC wafer roadmap looks very favorable as volume production takes off. For GaN materials the main application area is geared towards the lower power rating level up to 1 kV on mostly lateral FET designs. Power module demonstrations are beginning to appear in scientific reports and real applications. A short review is therefore given. Other advantages of SiC is the possibility of high temperature operation (> 300 degrees C) and in radiation hard environments, which could offer considerable system advantages.

This paper presents a novel method to extract the biasdependent series resistances and intrinsic conductance factor of individual MOS transistors from measured I-V characteristics. If applied to groups of scaled channel length devices, it also allows determination of the effective channel length together with the transversal field dependence of the carrier mobility. The method is exactly derived from conventional MOS theory based on the gradual channel approximation, and the deviations from such an ideal case are studied by means of two-dimensional device simulations. Experimental results obtained with n-and p-channel transistors of conventional as well as LDD type are presented to show the correctness of the proposed extraction procedure.

- by Enrico Sangiorgi
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- Physics, Parameter estimation, Uncertainty, Parameter Identification

The requirements for good MOSFET modeling are discussed, as they apply to usage in analog and mixed analogiligitsl design. A set of benchmark tests that can be easily performed by the reader are given, and it is argued that most CAD models today cannot pass all the tests, even for simple, long-channel devices at room temperature. A number of other problems are discussed, and in certain cases specific cures are suggested. The issue of parameter extraction is addressed. Finally, the context of model development and usage is considered, and it is argued that some of the factors responsible for the problems encountered in the modeling effort are of a nontechnical nature.

- by Ken Suyama
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- Analog Circuits, Computer Aided Design, Modeling, Analog Circuit Design

Low frequency noise measurements are among the most sensitive tools for the investigation of the quality and of the reliability of semiconductor devices. The sensitivity that can be obtained depends on the background noise of the low noise preamplifier coupled to the device under test (DUT) that, at very low frequencies, is dominated by flicker noise. The low frequency noise produced by the DUT, on the other end, is very often the most interesting signal to be detected and analyzed. In this work we propose a very simple topology for the realization of a general purpose low noise preamplifier whose noise performances, at very low frequencies (below 10 Hz), are significantly better than those that can be obtained by the most popular commercial instrumentation. Indeed, a gain of 80 dB with a pass band extending from a few tens of mHz up to a few kHz with an equivalent input voltage noise as low as 14 nV/square root(Hz) (100 mHz), 1.4 nV/square root(Hz) (1 Hz), 1.0 nV/square root(Hz) (10 Hz), and 0.8 nV/square root(Hz) (1 kHz) are consistently obtained by using quite standard electronic components and with no need for trimming and/or calibration steps. Moreover, the junction field-effect transistor input stage of the amplifier is characterized by an equivalent input current noise below 4 fA/square root(Hz) in the entire bandwidth, resulting in negligible background noise degradation for DUT impedances in excess of 100 kohms.

Carrier concentration profiles of two-dimensional electron gases are investigated in wurtzite, Ga-face and N-face heterostructures used for the fabrication of field effect transistors. Analysis of the measured electron distributions in... more

- by Martin Stutzmann
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- Engineering, III-V Semiconductors, Applied Physics, Atomic Force Microscopy

Two-dimensional (2D) plasma waves in field effect transistors are well known since the pioneer work of Dyakonov and Shur. The application to terahertz (THz) detection was proven recently both at cryogenic and room temperatures. Aside from these experiments, we used the interband photoexcitation brought by the difference-frequency component of a photomixed laser beam to excite very efficiently plasma waves in HEMT channel at room temperature. Owing to a specific experimental setup avoiding unwanted high-frequency electrical oscillations of the HEMTs, we obtained the spectral profiles of THz 2D plasma waves resonances of InGaAs HEMTs for many experimental conditions. The effect of geometrical HEMTs parameters (lengths of the gate and surrounding regions) as well as biasing conditions (drain and gate voltages) was evaluated on both plasma oscillations frequencies and amplitudes. Simultaneously, a numerical approach, based on hydrodynamic equations coupled to a pseudo-2D Poisson solver, was developed that compares well with experiments. Using this unique combination of experiments and numerical simulations, a comprehensive spectroscopy of plasma waves in HEMTs is thus obtained. It provides a deeper insight into the physical processes involved in plasma wave excitation and allows predicting for mixer operation at THz frequency only using the plasma wave nonlinearity. Mixing experiments are under progress.

- by Sylvain Bollaert
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- High Frequency, Numerical Simulation, Terahertz, Oscillations

According to aTop500.orgcompilation, large computer systems have been doubling in sustained speed every 1.14 years for the last 17 years. If this rapid growth continues, we will have computers by 2020 that can execute an Exaflop (1018) per second. Storage is also improving in cost and density at an exponential rate. Several innovations that will accompany this growth are reviewed here, including shrinkage of basic circuit components on Silicon, three-dimensional integration, and Phase Change Memory. Further growth will require new technologies, most notably those surrounding the basic building block of computers, the Field Effect Transistor. Implications of these changes for the types of problems that can be solved are briefly discussed.

- by Bruce Elmegreen
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- Three Dimensional, Phase Change Memory, Field effect transistor

A model is presented for the dynamic transconductance of small-channel-length MOSFET's operating in the linear region. The model includes the effects of interface traps and their frequency-depepdent admittance, Coulombic scattering due to all charges near the Si-Si02 interface, and surface roughness scatteriog. We use this model to explain the behavior of measured devices that have been submitted to ionizing radiation that introduces charges in the insulator and at the insulator-semiconductor interface. In particular, we show that the transconductance peak increases with the frequency of operation. The size of this effect is related mainly to the density of interface traps but is also controlled by the number of trapped charges near the Si-Si02 interface, which increases during irradiation. Static and high-frequency measurements of the transconductance of n-channel MOS-FET's are compared with simulated results using the proposed model.

- by Marvin White
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- RADIATION DAMAGE, Field effect transistors, Surface Roughness, High Frequency

This article summarizes and reviews the various preparation methods, physical properties, and potential applications of one-dimensional nanostructures of conjugated polyaniline (PANI), polypyrrole (PPY) and poly(3,4-ethylenedioxythiophene) (PEDOT). The synthesis approaches include hard physical template method, soft chemical template method, electrospinning, and lithography techniques. Particularly, the electronic transport (e.g., electrical conductivity, current-voltage (I-V) characteristics, magnetoresistance, and nanocontact resistance) and mechanical properties of individual nanowires/tubes, and specific heat capacity, magnetic susceptibility, and optical properties of the polymer nanostructures are presented with emphasis on size-dependent behaviors. Several potential applications and corresponding challenges of these nanofibers and nanotubes in chemical, optical and bio-sensors, nano-diodes, field effect transistors, field emission and electrochromic displays, super-capacitors and energy storage, actuators, drug delivery, neural interfaces, and protein purification are also discussed.

- by Zongwen Liu
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- Engineering, Protein Purification, Sensor, Drug delivery

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- by John Joannopoulos
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- Electrical Engineering, Electronics, Epitaxial Growth, Applied Research

Nanotransistors typically operate in far-fromequilibrium (FFE) conditions, that cannot be described neither by drift-diffusion, nor by purely ballistic models. In carbonbased nanotransistors, source and drain contacts are often characterized by the formation of Schottky Barriers (SBs), with strong influence on transport. Here we present a model for onedimensional field-effect transistors (FETs), taking into account on equal footing both SB contacts and FFE transport regime. Intermediate transport is introduced within the Büttiker's probe approach to dissipative transport, in which a non-ballistic transistor is seen as a suitable series of individually ballistic channels. Our model permits the study of the interplay of SBs and ambipolar FFE transport, and in particular of the transition between SB-limited and dissipation-limited transport.

- by Paolo Michetti
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- Microscopy, Nanoelectronics, Carbon Nanotubes, Nanotechnology
- by Yang-kyu Choi
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- Materials Science, Electronics, Nonlinear dynamics, Photonics
- by Erno Lindner
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- Quality Control, Nanowires, Solid State Electrochemistry, Microfabrication

The transformation of biochemical information into a physical or chemical signal is the basic idea behind a biosensor. The efficient detection of charged biomolecules by biosensor with appropriate device has caught tremendous research interest in the present decade. The present work is related to the simulation study of the performance of a functionalized surface of a biologically sensitive field-effect transistor. The detection process is less time consuming and less expensive as it combines a biological sensor and a measurement circuit in a small chip. In this model, a constant potential difference is maintained in between the two electrodes, one of which is functionalized with different types of biomolecules. With the number of double strand DNA oligomers, the concentration of Na + and Cl ions in the electrolyte in between the electrodes is changed, resulting in changes in surface charge density and dipole moment. Monte-Carlo simulation is performed in a neutral environment after...

- by Keka Talukdar
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- Chemistry, Nanoelectronics, Modeling and Simulation, Nanomaterials

Research in multigate silicon-on-insulator metal-oxide-semiconductor field-effect transistors (MOSFETs) for deep submicron complementary MOS applications is currently be-ing carried out by many semiconductor companies, as these devices... more

- by Nima Akhavan
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- Engineering, Applied Physics, Physical sciences, Fully Depleted

We present fabrication and characterization procedures of devices for circuit quantum electrodynamics (cQED). We have made 3 GHz cavities with quality factors in the range 10 4 − 10 6 , which allow access to the strong coupling regime of cQED. The cavities are transmission line resonators made by photolithography. They are coupled to the input and output ports via gap capacitors. An Al-based Cooper pair box is made by ebeam lithography and Dolan bridge double-angle evaporation in superconducting resonators with high quality factor. An important issue is to characterize the quality factor of the resonators. We present an RF-characterization of superconducting resonators as a function of temperature and magnetic field. We have realized different versions of the system with different boxcavity couplings by using different dielectrics and by changing the box geometry. Moreover, the cQED approach can be used as a diagnostic tool of qubit internal losses.

- by William Farr
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- Condensed Matter Physics, Kinetics, Electronic Materials, Electron Beam Lithography

O28. OGTRUMJIONIAVAIAUWIU'Y STATEMENT ,jI l01 Approved for Public Release, 92 9 1i 034I Distribution Unlimited 13. A5STNaC 0fjitxk 2Own ov__ Over the three-year course of this program, several issues in the device physics of resonant-tunneling diodes (RTDs) have been investigated, including the small-signal admittance, the shot noise, and the transport through multiple-quantum well structures. A large quantum-well inductance has been measured in the negative-differential-resistance region (NDR), but not in the positive-differentialresistance (PDR) region. The microwave shot-noise has been found to be suppressed relative to normal shot-noise in the PDR region, but enhanced in the NDR region. Triple-well RTDs have displayed a much wider NDR region in voltage than conventional single-well RTDs. Several new RTD material systems have been demonstrated including Type-Il InAs/AISb and Type-I GaSb/AISb, the first of which has yielded excellent properties for high-speed device applications. Studies of highly lattice mismatched InAs/AlSb RTDs on GaAs substrates have proven that the RTD characteristics are insensitive to a high density of dislocations. Finally, these results have been incorporated into the design of RTDs in high-frequency oscillators and high-speed switches. The InGaAs/AlAs RTD has been optimized for application in a quasioptical fundamental-frequency oscillator operating above 200 GHz. The same material system has been used to make a low-power RTD load for heterojunction field-effect and bipolar transistors in high-performance digital integrated circuits.

- by Elliott Brown
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- Density, Field effect transistors, High Frequency, Structures

Inorganic-organic composite and hybrid films find widespread applications for the development of functional materials. Polymer matrices with embedded inorganic fillers, nanoparticles or clusters are particularly appealing for optical, electronic, dielectric and magnetic applications. In particular, the development of hybrid layers with tailored dielectric properties represents a key issue in many technological fields. In this framework, poly(methyl methacrylate) (PMMA), due to its outstanding chemico-physical properties, represents a particularly suitable polymer component for the embedding of both microscopic and nanoscopic functional inorganic fillers. The wide use of such a matrix has to be traced back to the favourable combination of chemical and physical properties and easy processing. In this review, the main features and properties of PMMA, with a particular focus on dielectric ones, are firstly briefly described. Selected examples to illustrate the state-of-the art of its corresponding use as dielectric matrix are given and several examples are provided and surveyed. Finally, three case studies concerning PMMA-based hybrid films, produced for very different application fields, are described and discussed. The first example deals with the entrapment of micrometric zinc sulphide powders in PMMA, which acts as a host matrix for the electroluminescent particles in thick film-based Alternate Current Powder Electroluminescent Lamps (ACPELs). The second example describes the preparation of low-j inorganic-organic hybrid dielectric films based on a PMMA-polyvinylchloride(PVC) blend and a hydrophobic silica powder functionalised on the surface with trimethylsiloxane groups (m-SiO 2). The composition of the investigated materials is [(PMMA) x (PVC) y ]/(m-SiO 2) z with z ranging from 0 to 38.3 wt% and x = y = (100 À z)/2. The third case concerns the use of PMMA as a matrix to embed zirconium oxoclusters through the formation of covalent bonds. The obtained material, characterised by a dielectric constant value remarkably lower (1.93 at 1 kHz and 25°C) than in pristine PMMA (3.0 at 1 kHz and 25°C), appears as very appealing for the development of microelectronic devices based on low dielectric constant polymer films such as, for instance, field-effect transistor (FET).

- by fernando patolsky
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- Biosensors, Biomarkers, Life Sciences, Drug Discovery

We report that it is possible to establish well-defined semiconducting patterns in a perfluoro-alkyl functionalized fullerene (C60-F) film using a straightforward, benign and scalable method. The patterning technique comprises a direct laser light exposure of pre-select film areas, and a subsequent development in a heptane developer solution that selectively removes the non-exposed areas of the film. It is notable that no sacrificial photo-resist material is utilized, and that the remaining patterned C60-F material exhibits high electron mobility (>4 Â 10 À2 cm 2 /Vs, as quantified in transistor experiments) and improved ambient stability, both in comparison to the pristine material and to the more commonly utilized fullerene PCBM. We demonstrate that the patterning process has left the remaining C60-F material chemically unaltered, but that its degree of crystallinity has increased. The latter rationalizes the high electron mobility, the improved air stability, and the decreased solubility in the developer solution.

- by Thomas Wagberg
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- Engineering, Physics, Comparative Study, Organic Electronics

Noise in nanostructures is one of the key problems impeding their applications in electronic devices. We show that the level of 1 / f and recombination-generation noise in GaN nanowire field effect transistors can be suppressed by ultraviolet radiation by up to an order of magnitude. This strong suppression of the noise is explained by the illumination changing the occupancy of traps responsible for noise.

- by Michael Shur
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- Engineering, Physics, Applied Physics, Nanowires

This review describes recent groundbreaking results in Si, Si/SiGe and dopant-based quantum dots, and it highlights the remarkable advances in Si-based quantum physics that have occurred in the past few years. This progress has been possible thanks to materials development of Si quantum devices, and the physical understanding of quantum effects in silicon. Recent critical steps include the isolation of single electrons, the observation of spin blockade and single-shot read-out of individual electron spins in both dopants and gated quantum dots in Si. Each of these results has come with physics that was not anticipated from previous work in other material systems. These advances underline the significant progress towards the realization of spin quantum bits in a material with a long spin coherence time, crucial for quantum computation and spintronics. CONTENTS 42 3. Interactions between donors 43 D. Double dopant quantum dots 43 E. Charge sensing in few-electron dopants 43 VI. Relaxation, coherence and measurements 44 A. Spin relaxation and decoherence 45 1. Electron spin relaxation in donors 46 2. Electron spin relaxation in quantum dots 47 3. Singlet-triplet relaxation 47 4. Spin decoherence 48 B. Orbital and valley relaxation 49 C. Control and readout of spins in silicon 50 1. Bulk spin resonance 50 2. Electrically-detected magnetic resonance 51 3. Single-shot readout of a single electron spin 51 4. Readout and control of singlet-triplet states in double quantum dots 53 5. Single-atom spin qubit 54 VII. Outlook 54 Acknowledgments 55 References 55 1 We refer to other review articles on quantum dots and singleelectron transistors for more background and details: Beenakker and van Houten (1991);

- by Gerhard Klimeck
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- Modern physics, Physical sciences, Room Temperature, Field effect transistor

This paper describes an observed difference in how DC-RF dispersion manifests itself in AlGaN/GaN HFETs when the devices are driven into different RF load impedances. The localised nature of the dispersion on the IV plane has been observed in RF waveform measurements and is explained through physical modelling. The difference in dispersive behaviours has been attributed to the geometry of the trap induced virtual gate region and the resulting carrier velocity saturation being overcome by punch through effects under high electric fields.

- by Johannes Benedikt
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- Gallium nitride, Radio Frequency, Physical Modelling, Electron Devices

Metal-oxide-semiconductor heterostructure field effect transistors (MOSHFETs) were fabricated with an AlN/GaN heterostructure grown on Si substrates. A 7-nm Al 2 O 3 serving as both gate dielectric under the gate electrode and passivation layer in the access region was used. It was found that the Al 2 O 3 was superior to SiN x in increasing the 2-D electron gas (2DEG) density and thereby reducing the access resistance. In addition, the OFF-state leakage current (I off ) in these AlN/GaN MOSHFETs was reduced by four orders of magnitude to 7.6 × 10 −5 mA/mm as a result of the Al 2 O 3 gate dielectric, compared to that of AlN/GaN HFETs. Meanwhile, the subthreshold slope was improved to a nearly ideal value of 62 mV/dec because of the extremely low I off . The MOSHFETs with 1-μm gate length exhibited good DC characteristics. A maximum drain current of 745 mA/mm and a peak extrinsic transconductance of 280 mS/mm were achieved.

- by Kei Lau
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- Gallium nitride, Leakage Current, Aluminum oxide, Logic Gate
- by majid alasadi
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- Engineering, Materials Science, Frequency, Induction Heating

Flexible and high-aspect-ratio C 60 nanorods are synthesized using a liquid-liquid interfacial precipitation process. As-grown nanorods are shown to exhibit a hexagonal close-packed single-crystal structure, with m-dichlorobenzene solvent molecules incorporated into the crystalline structure in a C 60 :m-dichlorobenzene ratio of 3:2. An annealing step at 200 • C transforms the nanorods into a solvent-free face-centred-cubic polycrystalline structure. The nanorods are deposited onto field-effect transistor structures using two solvent-based techniques: drop-casting and dip-coating. We find that dip-coating deposition results in a preferred alignment of non-bundled nanorods and a satisfying transistor performance. The latter is quantified by the attainment of an electron mobility of 0.08 cm 2 V −1 s −1 and an on/off ratio of >10 4 for a single-crystal nanorod transistor, fabricated with a solution-based and low-temperature process that is compatible with flexible substrates.

We present a systematic approach to reduce the resistance of ohmic contacts on AlGaN/GaN FET structures. We have optimised the Ti/Al/Ni/Au contact with respect to the metal composition and annealing conditions. Our optimised contact has a very low contact resistance of 0.2 O mm (7.3 Â 10 À7 O cm 2), a good reproducibility and an excellent line definition, making this contact very suitable for use in AlGaN/GaN FETs with short gate-source distances. This

- by Fouad Karouta
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- Crystal Growth, Semiconductor Devices, Contact Resistance, Ohmic Contact

Poly(3-hexylthiophene)/poly(methyl methacrylate) (P3HT/PMMA) blends were used as the semiconducting layer in water-gated organic field-effect transistors (OFETs), which resulted in improving the electrical performance of the previously reported devices with pure P3HT. Topographic investigations by atomic force microscopy carried out on blends with various PMMA to P3HT ratio reveal a lateral phase separation of the two components. All transistors operate at very low voltage (below 1 V), with a threshold voltage ranging form 0.3 to 0.5 V. An optimum of the composition of the blend is found with 70% of PMMA, leading to a maximum on/off current ratio and a mobility comparable to that of pure P3HT.

- by Benoit PIRO
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- Engineering, Water, Organic Electronics, Atomic Force Microscopy

By scanning a positively biased conductive AFM tip in contact mode at LaAlO 3 top surface, nanoscale patterns of conductive regions can be written at the interface between LaAlO 3 and SrTiO 3 at room temperature. by scanning the same area with negatively biased AFM probe. Conductive nanowires as narrow as 2.1 nm and Isolated dots as small as 1 nm have been created.

- by Cheng cen
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- Nanoelectronics, Science, Science and Technology, Atomic Force Microscopy

Adaptive biases are proposed for both the drain and the dummy gate of LDMOSFETs to improve their overall efficiency in amplification of highly modulated signals. At low input power, the drain bias is reduced to maintain high efficiency. At high input power, the dummy-gate bias is increased to maintain high linearity. By using such adaptive biases on both the drain and dummy gate, the measured efficiency on an LDMOSFET for a signal with a 9-dB peak-to-average modulation ratio is 16 percentage units higher than that with fixed biases and 5 percentage units higher than that with adaptive bias on the drain alone.

- by Ayman Shibib
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- Power Electronics, Adaptive Control, Low Power Electronics, Feedforward

We report that solution-based treatment of Cu electrodes with strong electron acceptor molecules significantly decreases the contact resistance towards organic semiconductors, which is advantageous for applications such as organic field-effect transistors (OFETs). Spin-coating solutions of tetracyanoquinodimethane (TCNQ) or tetrafluoro-tetracyanoquinodimethane (F4-TCNQ) onto Cu electrodes results in strongly chemisorbed acceptor (sub-)monolayers, which increase the electrode work function from 4.5 eV (bare Cu) up to 5.2 eV (F4-TCNQ-treated) even in air, as evidenced by X-ray photoelectron spectroscopy and photoelectron yield spectroscopy. The use of such modified electrodes in flexible OFETs with poly(3-hexylthiophene)-dithienyltetrafluorobenzene (P3HT-TFT) as semiconductor lead to a twofold increase of the on-current in the saturation regime and a decrease of the threshold voltage from À20 V (bare Cu) to À7 V (F4-TCNQ-treated). These results confirm that this simple solution-based process is viable for lowering organic/metal contact resistances in organic electronic devices.

- by Silvia Janietz
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- Engineering, Organic Semiconductors, Organic Electronics, Field effect transistors

Simulation results are presented for a MOSFET with position and energy (potential) dependent interface trap distributions which may be typical for devices subjected to interface trap producing processes such as hot-electron degradation. The interface trap distribution is modeled as a Gaussian peak at a given position along the channel while the energy dependence is derived from C-V measurements from an MOS capacitor exposed to ionizing radiation. A novel fixed-point technique is used to solve the two-dimensional boundaryvalue problem. The technique is shown to be globally convergent for arbitrary distributions of interface traps. A comparison of the convergence properties of the Newton and fixed-point methods is presented, and it is shown that for some important cases the Newton technique fails to converge while the fixed-point technique converges with a geometric convergence rate.

- by Professor Can E. Korman
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- Iterative Methods, Differential Equations, Simulation, Degradation
- by Igor Jovanovic
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- Nanotechnology, Field effect transistors, Films, Resistance

The manipulation of the electron spin degree of freedom is at the core of the spintronics paradigm, which offers the perspective of reduced power consumption, enabled by the decoupling of information processing from net charge transfer. Spintronics also offers the possibility of devising hybrid devices able to perform logic, communication, and storage operations. Graphene, with its potentially long spin-coherence length, is a promising material for spin-encoded information transport. However, the small spin-orbit interaction is also a limitation for the design of conventional devices based on the canonical Datta-Das spin-FET. An alternative solution can be found in magnetic doping of graphene, or, as discussed in the present work, in exploiting the proximity effect between graphene and Ferromagnetic Oxides (FOs). Graphene in proximity to FO experiences an exchange proximity interaction (EPI), that acts as an effective Zeeman field for electrons in graphene, inducing a spin precession around the magnetization axis of the FO. Here we show that in an appropriately designed double-gate field-effect transistor, with a bilayer graphene channel and FO used as a gate dielectric, spin-precession of carriers can be turned ON and OFF with the application of a differential voltage to the gates. This feature is directly probed in the spin-resolved conductance of the bilayer.

- by Paolo Michetti
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- Field effect transistors, Multidisciplinary, Doping, Information Processing

A mode space (MS) tight binding approach for the simulation of armchair graphene nanoribbon FETs is discussed. It makes use of slab-dependent modes and a novel criterion for mode selection, going beyond the one based on the lowest energy subbands. For ideal ribbons, we show that by splitting the modes into decoupled groups, the new method provides results almost identical to the real space (RS) with a speedup of more than one order of magnitude. Even in the presence of edge roughness, which tends to couple the modes, the MS approach still offers a sizable computational advantage with respect to the RS, while retaining a good accuracy. Index Terms-Graphene nanoribbon (GNR) FETs, mode-space (MS) approach, nonequilibrium Green's functions (NEGF), tight binding (TB) Hamiltonian.

- by G. Baccarani
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- Engineering, Physics, Materials Science, Art
- by Stephane Pleutin
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- Engineering, Nanoelectronics, Modeling, Nanoparticle
- by Anthony Parker
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- Engineering, Memory Effect, Harmonic distortion, Intermodulation Distortion

The effect of optical radiation and surface recombination on the characteristics of an ion-implanted GaAs MESFET is studied analytically in the below-pinchoff region. Results show that optical radiation significantly enhances the drain-source current of the GaAs MESFET when only electron-bole pair generation is considered. However, the surface recombination, which in turn results in a gate leakage current, reduces the drain-source current depending on the density of trap centers. The threshold voltage is found to decrease under the normally OFF condition and increase under the normally ON condition due to photogenerated carriers. The surface recombination reverses the effect, i.e., threshold voltage increases under the normally OFF condition and decreases under the normally ON condition, with the increase in the trap center density at a particular ion dose compared to those cases where the effect of recombination is not considered.

- by Sunita Mishra
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- Leakage Current, Ion Implantation, Radiation Effect, Gallium Arsenide

We present an analytical procedure to perform the local noise analysis of a semiconductor junction when both the drift and diffusive parts of the current are important. The method takes into account space-inhomogeneous and hot-carriers conditions in the framework of the drift-diffusion model, and it can be effectively applied to the local noise analysis of different devices: n ϩ nn ϩ diodes, Schottky barrier diodes, field-effect transistors, etc., operating under strongly inhomogeneous distributions of the electric field and charge concentration.

- by Gabriel Gomila
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- Engineering, Applied Physics, Mathematical Sciences, Physical sciences

- by Elliott Brown
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- Density, Field effect transistors, High Frequency, Structures

The traditional monostable-bistable transition logic element (MOBILE) structure is usually composed of resonant tunneling diodes (RTD). This letter describes a new type MOBILE structure consisting of singleelectron transistors (i.e. SET-MOBILE). The analytical model of single-electron transistors(SET)has been considered three states (including an excited state) of the discrete quantum energy levels. The simulation results show negative differential conductance (NDC) characteristics in I DS-V DS curve. The SET-MOBILE utilizing NDC characteristics can successfully realize the basic logic functions as the RTD-MOBILE.

Mobility profiles of GaAs power MESFET's have been measured using the magnetotransconductance technique. Unliklt devices with small gate widths, large periphery power devices exhibi: significant parasitic resistance effects, and corrections have to he n alde. To obtain a realistic mobility profile of the channel, precise meal urement of the magnetic field dependence of the transconductance :and parasitic resistance is necessary. The technique for obtaining thes: accurate measurements is detailed. The FET's studied are standarc microwave power devices for amplifier circuit applications. Devices having gate peripheries of up to 3.5 mm have been studied, and corrected mobility in the range of 3500-6000 cm2 / V . s has been obtained.