Values Of Gate Voltage Research Articles

Improvement of device isolation using field implantation for GaN MOSFETs

Gallium nitride (GaN) metal-oxide-semiconductor field-effect transistors (MOSFETs) with boron field implantation isolation and mesa isolation were fabricated and characterized. The process of boron field implantation was altered and subsequently conducted after performing high-temperature ohmic annealing and gate oxide thermal treatment. Implanted regions with high resistivity were achieved. The circular MOSFET fabricated in the implanted region showed an extremely low current of 6.5 × 10−12 A under a gate voltage value up to 10 V, thus demonstrating that the parasitic MOSFET in the isolation region was eliminated by boron field implantation. The off-state drain current of the rectangular MOSFET with boron field implantation was 5.5 × 10−11 A, which was only one order of magnitude higher than the 6.6 × 10−12 A of the circular device. By contrast, the rectangular MOSFET with mesa isolation presented an off-state drain current of 3.2 × 10−9 A. The field isolation for GaN MOSFETs was achieved by using boron field implantation. The implantation did not reduce the field-effect mobility. The isolation structure of both mesa and implantation did not influence the subthreshold swing, whereas the isolation structure of only the implantation increased the subthreshold swing. The breakdown voltage of the implanted region with 5 μm spacing was up to 901.5 V.

Performance Optimization of Conventional CNTFETs Based on Asymmetric Lightly Doped Source and Drain Regions

Carbon nanotube (CNT) could be exploited as a channel or source/drain region in field effect transistors (FETs). We theoretically investigate the impact of Source and Drain doping level on a coaxially gated CNTFET's performance in the ballistic regime. The results show that the On/Off Ratio, Subthreshold swing, Cutoff Frequency, transconductance and delay are improved with choosing the source and drain doping structure. It seems that the most important impact of Source and Drain doping level and length is the reason of change and shift in the transfer characteristics of the device simulation results values. However, form this paper it is possible to choose an optimal value of CNTFET Gate voltage and gate length to obtain better performance.

Dual Gate Tunable and High Responsivity Graphene‐Based Field Effect Transistors

SummaryThe output characteristics of a dual gated depletion mode, n‐channel graphene field effect transistor (n‐Gr‐FET) are simulated to understand the unipolar Ids–Vds behavior for different values of gate voltages, (Vback and Vtop). In our results, the saturated drain‐source current (Ids) varies from 0.001 to 100 µA/µm, 9 to 125 µA/µm and 16 to 135 µA/µm as Vback is varied from 5 to 40 V with correspondingly Vtop of 0, 2 and 10 volts. Consequently, there is four to eight times enhancement in estimated mobility for varying Vback from 5 to 40V. The unipolar saturation in Ids at higher values of Vds can be understood from the compensation of parallel Vds and transverse (Vback−Vtop) electric fields. Furthermore, the channel length modulation (increase in Ids for Vtop > 0) supported by the increase in mobility, is observed because of reverse junction formation at the vicinity of the drain and gate terminal. The results signify that the dual gated n‐Gr‐FET, at optimum Vback, modulates the unipolar characteristics in channel region. Thus, making n‐Gr‐FET a potential candidate to stipulate the demand of low power, high performance functionalities in nano‐electronic applications.

Sub-threshold-like charge transport in organic field effect transistor: A study on effective channel thickness

A short channel organic field effect transistors (OFET) based on Pentacene, having channel length in the range of sub-micrometer, has been numerically modelled for low values of drain voltage. The output characteristics show a nonlinear concave increase of drain current for all values of gate voltages. This anomalous current-voltage behavior, which resembles sub-threshold characteristics of silicon FETs, shows a good match with earlier experimental reports on OFET at low drain voltages. The sub-threshold-like characteristics has been interpreted in light of thermionic-emission model because of the presence of hole injection barrier at drain (gold)/Pentacene interface. The associated analysis has facilitated to obtain a significant parameter, effective channel thickness [Formula: see text], for the first time in case of OFETs. It came out to be roughly 4 nm and 8 nm for experimental devices of poly(3-hexylthiophene-2,5-diyl) and Pentacene, respectively, while the numerically modelled device yielded a value of about 60 nm. Increase of [Formula: see text] with transverse gate electric field is also observed. Physical explanation of the observations is also presented.

Empirical Modeling of a Graphene Field-Effect Transistor Sensor

This theoretical nanoscience work explore the empirical method of extracting experimental radiation sensor data from published work and project the performance limit of the sensor in term of back gate voltage, resistance and radiation flux. We demonstrate an empirical regression modeling of an X-ray radiation sensor based on a graphene field effect transistor (GFET). The experimental data obtained from published work only showed the values of resistance, R versus back gate voltage, Vbg for X-ray flux, E of 0 kV, 30 kV and 40 kV. Least Squares Estimation (LSE) in nonlinear regression model is utilized to obtain the individual polynomial regression model of resistance versus back gate voltage model for each of the 3 X-ray flux. LSE with multiple nonlinear regression incorporating with Nimmo and Atkinsmethod is employ to get a unified polynomial regression based on the individual model. The model is simulated in MATLAB and provide fast execution time. The unified model for is able to predict the resistance versus back gate voltage for various X-ray radiation flux beyond these three values given values. In addition to that, we are able to find the limit of X-ray flux based on the initial characteristic. Moreover, our technique enable one to visualize the interrelationship between R, Vbg and E variables and perform multivariate analysis. The empirical regression model of GFET is shown to have good agreement with experimental data and theoretical prediction for multivariate such as back gate voltage, resistance and X-ray flux.

플로팅 게이트형 유기메모리 동작특성

Abstract Organic memory devices were made using the plasma polymerization method. The memory device consistedof ppMMA(plasma polymerization MMA) thin films as the tunneling and insulating layer, and a Au thin film as the memory layer, which was deposited by thermal evaporation. The organic memory operation theory was developed according to the charging and discharging characteristics of floating gate type memory, which would be measuredby the hysteresis voltage and memory voltage with the gate voltage values. The I-V characteristics of the fabricatedmemory device showed a hysteresis voltage of 26 [V] at 60 ∼ -60 [V] double sweep measuring conditions. The programming voltage was applied to the gate electrode in accordance with the result of this theory. A programmingvoltage of 60[V] equated to a memory voltage of 13[V], and 80[V] equated to a memory voltage of 18[V]. The memory voltage of approximately 40 [%]increased with increasing programming voltage. The charge memory layer charging or discharging according to the theory of the memory was verified experimentally.

A Single Electron Transistor Made From Lead Cadmium Selenide Nanocrystals

With the miniaturization of transistor size, fabrication of transistor with lithography technique is a foreseen problem. It is possible to routinely create semiconductor nanocrystals whose dimensions are much smaller than those can be realized by lithography techniques using colloidal chemistry. The size of the nanocrystals can be varied easily by varying the process parameters to study the quantum confinement effect. Here we present the simple synthesis method of Pb-CdSe and characterization of the same with XRD, UV-VIS spectroscopy and AFM. Also we present the I-V characteristics of Single Electron Transistor, by applying different values of Gate voltage. Decrease in the size of the nanoparticles will result in increase in charging energy and hence leads to more prominent Coulomb Blockade phenomena. Gate voltage controls the movement of electron from the blockade region and hence can be used in charge sensing application as they detect the motion of single electron.

Temperature Influence on Nanowire Tunnel Field Effect Transistors

This work presents a study of the temperature impact on the performance of nanowire tunnel field effect transistors (TFETs). After explaining the fundamental working principles based on simulated energy band diagrams, experimental data were analyzed for temperatures ranging from 300 to 420 K. Therefore, it was possible to evaluate the TFET performance regarding the subthreshold slope (S) and the on-state and off-state current ratio (ION/IOFF) for different nanowire diameters and bias conditions. The drain current susceptibility to the temperature can be explained based on the influence of each of the most relevant transport mechanisms (band-to-band tunneling, trap-assisted tunneling and Shockley-Read-Hall generation/recombination). The resulting subthreshold slopes in the different regions were compared to the 60 mV/dec limit at room temperature for standard MOSFET devices. It was observed that the ION/IOFF ratio increased for larger nanowire diameters but decreased for higher temperatures. Drain current was reported to be much less influenced by the temperature for higher gate voltage values, when band-to-band tunneling prevailed over the other components.

Ultraviolet photoresponse of ZnO nanowire thin-film transistors

Thin-film transistors (TFTs) based on ZnO nanowire (NW) film are fabricated and used as ultraviolet (UV) photodetectors. The decay time constants and the ratio of photocurrent to dark current do not reach their own optimum value under the same conditions, and so a compromise between them should be decided with appropriate values of gate voltages and drain-source voltages. A negative gate voltage applied to the UV photodetectors causes the energy band tilting toward the interface of thin film/air, which make the free electrons in NWs migrate to the interface of thin film/air along the potential gradient and so promotes the depletion of free electrons by adsorption of oxygen molecules. A positive gate voltage applied before the normal time-resolved measurement of photoresponse can make additional oxygen molecules remain in close proximity to the surface of ZnO NWs, which leads to the decrease of the decay time constant. The decay time constant can be greatly decreased by applying a negative gate voltage to the device in the process of time-resolved measurement of photoresponse and a positive gate voltage in advance.

(Invited) Electroluminescence in Metal-Oxide-Semiconductor Tunnel Diodes with Nanometer-Thick Silicon

Electroluminescence in metal-oxide-semiconductor tunnel diodes with a transparent conductive oxide gate and a nanometer-thick silicon layer on silicon-on-insulator substrates has been studied. The electroluminescence spectra from the diodes are peaked at ~1120 nm (~1.11 eV). The peak shifts toward lower energy as the negative gate voltage value increases. The peak shift can be explained by a Stark effect. The peak tail intensity at the short-wavelength side of the peak at ~1120 nm increases as the silicon layer thickness decreases. This may indicate that the increase in the intensity is due to transitions between subbands near the silicon band edges. Small peaks have been observed at ~1050 nm (~1.18 eV) and ~1010 nm (~1.23 eV). The peak wavelengths are independent of the silicon layer thickness. This exhibits that the electroluminescence is due to defect-mediated transitions.

Transport properties of graphene quantum dots

In this work we present a theoretical study of transport properties of a double crossbar junction composed by segments of graphene ribbons with different widths forming a graphene quantum dot structure. The systems are described by a single-band tight binding Hamiltonian and the Green's function formalism using real space renormalization techniques. We show calculations of the local density of states, linear conductance and I-V characteristics. Our results depict a resonant behavior of the conductance in the quantum dot structures which can be controlled by changing geometrical parameters such as the nanoribbon segments widths and relative distance between them. By applying a gate voltage on determined regions of the structure, it is possible to modulate the transport response of the systems. We show that negative differential resistance can be obtained for low values of gate and bias voltages applied.

Stochastic dynamics for a single vibrational mode in molecular junctions

We propose a very accurate computational scheme for the dynamics of a classical oscillator coupled to a molecular junction driven by a finite bias, including the finite mass effect. We focus on two minimal models for the molecular junction: Anderson-Holstein (AH) and two-site Su-Schrieffer-Heeger (SSH) models. As concerns the oscillator dynamics, we are able to recover a Langevin equation confirming what found by other authors with different approaches and assessing that quantum effects come from the electronic subsystem only. Solving numerically the stochastic equation, we study the position and velocity distribution probabilities of the oscillator and the electronic transport properties at arbitrary values of electron-oscillator interaction, gate and bias voltages. The range of validity of the adiabatic approximation is established in a systematic way by analyzing the behaviour of the kinetic energy of the oscillator. Due to the dynamical fluctuations, at intermediate bias voltages, the velocity distributions deviate from a gaussian shape and the average kinetic energy shows a non monotonic behaviour. In this same regime of parameters, the dynamical effects favour the conduction far from electronic resonances where small currents are observed in the infinite mass approximation. These effects are enhanced in the two-site SSH model due to the presence of the intermolecular hopping t. Remarkably, for sufficiently large hopping with respect to tunneling on the molecule, small interaction strengths and at intermediate bias (non gaussian regime), we point out a correspondence between the minima of the kinetic energy and the maxima of the dynamical conductance.

Performance analysis of long Ge channel double gate (DG) p MOSFETs with high- k gate dielectrics based on carrier concentration formulation

In this paper, electrical behavior of symmetric double gate Ge channel MOSFETs with high- k dielectrics is reported on the basis of carrier concentration formalism. The model relies on the solution of Poisson–Boltzmann equations subject to suitable boundary conditions taking into account the effect of interface trap charge density ( D it ) and the Pao-Sah’s current formulation considering field dependent hole mobility. It is continuous as it holds good for sub-threshold, weak and strong inversion regions of device operation. The proposed model has been employed to calculate the drain current of DG MOSFETs for different values of gate voltage and drain voltage along with various important device parameters such as transconductance, output conductance, and transconductance per unit drain current for a wide range of interface trap charge density, equivalent oxide thickness (EOT) and bias conditions. Moreover, most of the important device parameters are compared with their corresponding Si counter parts. Accuracy of the model has been verified by comparing analytical results with the numerical simulation data. A notable improvement of the drive current and transconductance for Ge devices is observed with reference to Si devices, particularly when D it is small.

Electrical characterization of high-k based metal-insulator-semiconductor structures with negative resistance effect when using Al2O3 and nanolaminated films deposited on p-Si

In this work, the results of the electrical behavior of metal-insulator-semiconductor (MIS) structures using Al2O3, HfO2, and nanolaminated layers as gate insulators are reported. The MIS structures were deposited by atomic layer deposition on several Si substrates. The authors observed different conduction mechanisms for these high-k based MIS structures depending on the bias regime. Direct tunneling, Fowler–Nordheim, Poole–Frenkel emission, and a negative resistance region have been observed at different gate voltage values. The tunneling conduction of majority and minority carriers assisted by defects located at the Al2O3/HfO2 and Al2O3/metal interfaces can explain the negative resistance behavior observed in Al2O3 and nanolaminated samples. In addition to current-voltage (I-V) measurements, MIS structures were also electrically characterized using capacitance-voltage (C-V), deep level transient spectroscopy, conductance transients (G-t), and flat-band voltage transient (VFB-t) techniques.

Influence of Atmospheric Gases on the Electrical Properties of PbSe Quantum-Dot Films

We report the effects of N2 and O2 on the electrical properties of PbSe quantum-dot (QD) films treated with 1,2-ethanedithiol (EDT) by measuring the changes in the current−voltage characteristics of QD field-effect transistors (FETs). EDT-treated PbSe QD films at a base pressure of ∼10−5 Torr exhibit ambipolar transport. Exposing these films to N2 shifts the transfer characteristics toward negative gate-voltage values and increases the electron mobility. These changes could be reversed entirely by removing the N2 gas over the FET and returning to base pressure. Oxygen exposure shifts the transfer characteristics in the opposite direction toward positive gate-voltage values. Moreover, oxygen exposure reduces charge mobility but increases film conductivity. For exposures up to ∼108 langmuir, these O2-induced changes could be reversed completely by removing the O2 gas over the sample and returning to base pressure. However, after ∼1010 langmuir of O2 exposure, the changes are irreversible. The QD films then ...

Tunable electrical superlattices in periodically gated bilayer graphene

The paper demonstrates that a single flake of bilayer graphene patterned with a periodic array of metallic gate electrodes behaves like a programmable superlattice formed by heterostructures of type I, II, or III, depending on the dc gate voltage values. The engineering of the width and position of the band gap in each region is performed only by tuning the dc voltages applied on the gate electrodes. Such a single programmable superlattice on bilayer graphene could replace the existing superlattices that require different semiconductor materials for each heterostructure type.

Mechanisms of Hot-Carrier-Induced Threshold-Voltage Shift in High-Voltage p-Type LDMOS Transistors

The phenomena and mechanisms of hot-carrier-induced threshold-voltage ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> ) shift in high-voltage p-type laterally diffused MOS (LDMOS) transistors are investigated. At low-| <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">gs</sub> | (absolute value of gate voltage) stress condition, electrons are injected and trapped in the gate oxide at the channel region near the drain, resulting in <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> increase (Delta|V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> | < 0). At high-| <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">gs</sub> | stress condition, however, severe <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> decrease (Delta|V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> | > 0) is found after stress. Experimental results suggest that donor-type interface traps created by hole injection in the channel region is the dominant factor for <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> decrease.

Self-consistent Wigner distribution function study of gate-voltage controlled triple-barrier resonant tunnelling diode

The electron transport through the triple-barrier resonant tunnelling diode (TBRTD) has been studied by the self-consistent numerical method for the Wigner–Poisson problem. The electron flow through the TBRTD can be controlled by the gate voltage applied to one of the potential well regions. For different gate voltage values we have determined the current–voltage characteristics, potential energy profiles and electron density distribution. We have found the enhancement of the peak-to-valley ratio (up to ∼10), the appearance of the linear current versus bias voltage behaviour within the negative-differential resistance region and the bistability of the current–voltage characteristics. We provide a physical interpretation of these results based on the analysis of the self-consistent potential profiles and electron density distribution.

Impact of classical forces and decoherence in multiterminal Aharonov-Bohm networks

Multi-terminal Aharonov-Bohm (AB) rings are ideal building blocks for quantum networks (QNs) thanks to their ability to map input states into controlled coherent superpositions of output states. We report on experiments performed on three-terminal GaAs/Al_(x)Ga_(1-x)As AB devices and compare our results with a scattering-matrix model including Lorentz forces and decoherence. Our devices were studied as a function of external magnetic field (B) and gate voltage at temperatures down to 350 mK. The total output current from two terminals while applying a small bias to the third lead was found to be symmetric with respect to B with AB oscillations showing abrupt phase jumps between 0 and pi at different values of gate voltage and at low magnetic fields, reminiscent of the phase-rigidity constraint due to Onsager-Casimir relations. Individual outputs show quasi-linear dependence of the oscillation phase on the external electric field. We emphasize that a simple scattering-matrix approach can not model the observed behavior and propose an improved description that can fully describe the observed phenomena. Furthermore, we shall show that our model can be successfully exploited to determine the range of experimental parameters that guarantee a minimum oscillation visibility, given the geometry and coherence length of a QN.

Organic field-effect transistors for biosensing applications

Organic field-effect transistors (OFETs) with regioregular poly(3-hexylthiophene) (P3HT) have been designed and fabricated aiming at the lowest possible working point (i.e. the adjusted values of gate voltage and drain–source voltage) for the use as sensor in electrolytes. Using thermally grown silicondioxide with a thickness of 45 nm it has been possible to dramatically lower the gate potential. Even around one volt the channel current and its modulation are still large enough for detection with simple operational amplifiers. The experimental results indicate a strong dependence of the transistor performance on the solvent used for spin coating the organic film. A theoretical analysis based on an analytical model allowed us to relate the different behavior of the transistor to their mobility, which is in turn dependent on the density of traps. In the context of this paper the leakage currents – as a non-zero gate current – have been analyzed. The observed gate leakage currents of the electrode structures themselves as well as of the complete transistors can be well described by Fowler’s and Nordheim’s field enhanced tunneling.