Schottky-barrier Field-effect Transistors Research Articles

Applications of Multi-Terminal Memristive Devices: A Review

Memristive devices have the potential for a complete renewal of the electron devices landscape, including memory, logic and sensing applications. This is especially true when considering that the memristive functionality is not limited to two-terminal devices, whose practical realization has been demonstrated within a broad range of different technologies. For electron devices, the memristive functionality can be generally attributed to a state modification, whose dynamics can be engineered to target a specific application. In this review paper, we show examples of two-terminal Resistive RAMs (ReRAM) for standalone memory and Field Programmable Gate Arrays (FPGA) applications. Moreover, a Generic Memory Structure (GMS) utilizing two ReRAMs for 3D-FPGA is discussed. In addition, we show that trap charging dynamics can explain some of the memristive effects previously reported for Schottky-barrier field-effect Si nanowire transistors (SB SiNW FETs). Moreover, the SB SiNW FETs do show additional memristive functionality due to trap charging at the metal/semiconductor surface. The combination of these two memristive effects into multi-terminal MOSFET devices gives rise to new opportunities for both memory and logic applications as well as new sensors based on the physical mechanism that originate memristance. Finally, the multi-terminal memristive devices presented here have the potential of a very high integration density, and they are suitable for hybrid CMOS co-fabrication with a CMOS-compatible process.I.

Ultrashort Channel Silicon Nanowire Transistors with Nickel Silicide Source/Drain Contacts

We demonstrate the shortest transistor channel length (17 nm) fabricated on a vapor-liquid-solid (VLS) grown silicon nanowire (NW) by a controlled reaction with Ni leads on an in situ transmission electron microscope (TEM) heating stage at a moderate temperature of 400 °C. NiSi(2) is the leading phase, and the silicide-silicon interface is an atomically sharp type-A interface. At such channel lengths, high maximum on-currents of 890 (μA/μm) and a maximum transconductance of 430 (μS/μm) were obtained, which pushes forward the performance of bottom-up Si NW Schottky barrier field-effect transistors (SB-FETs). Through accurate control over the silicidation reaction, we provide a systematic study of channel length dependent carrier transport in a large number of SB-FETs with channel lengths in the range of 17 nm to 3.6 μm. Our device results corroborate with our transport simulations and reveal a characteristic type of short channel effects in SB-FETs, both in on- and off-state, which is different from that in conventional MOSFETs, and that limits transport parameter extraction from SB-FETs using conventional field-effect transconductance measurements.

Transistors with chemically synthesized layered semiconductor WS2 exhibiting 105 room temperature modulation and ambipolar behavior

We report the realization of field-effect transistors (FETs) made with chemically synthesized multilayer crystal semiconductor WS2. The Schottky-barrier FETs demonstrate ambipolar behavior and a high (∼105×) on/off current ratio at room temperature with current saturation. The behavior is attributed to the presence of an energy bandgap in the ultrathin layered semiconductor crystal material. The FETs also show clear photo response to visible light. The promising electronic and optical characteristics of the devices combined with the chemical synthesis, and flexibility of layered semiconductor crystals such as WS2 make them attractive for future electronic and optical devices.

Effect of a gate buffer layer on the performance of a 4H-SiC Schottky barrier field-effect transistor

A lower doped layer is inserted between the gate and channel layer and its effect on the performance of a 4H-SiC Schottky barrier field-effect transistor (MESFET) is investigated. The dependences of the drain current and small signal parameters on this inserted gate-buffer layer are obtained by solving one-dimensional (1-D) and two-dimensional (2-D) Poisson's equations. The drain current and small signal parameters of the 4H-SiC MESFET with a gate-buffer layer thickness of 0.15 μm are calculated and the breakdown characteristics are simulated. The results show that the current is increased by increasing the thickness of the gate-buffer layer; the breakdown voltage is 160 V, compared with 125 V for the conventional 4H-SiC MESFET; the cutoff frequency is 27 GHz, which is higher than 20 GHz of the conventional structure due to the lower doped gate-buffer layer.

Multiterminal Memristive Nanowire Devices for Logic and Memory Applications: A Review

Memristive devices have the potential for a complete renewal of the electron devices landscape, including memory, logic, and sensing applications. This is especially true when considering that the memristive functionality is not limited to two-terminal devices, whose practical realization has been demonstrated within a broad range of different technologies. For electron devices, the memristive functionality can be generally attributed to a material state modification, whose dynamics can be engineered to target a specific application. In this review paper, we show that trap charging dynamics can explain some of the memristive effects previously reported for Schottky-barrier field-effect Si nanowire transistors (SB SiNW FETs). Moreover, the SB SiNW FETs do show additional memristive functionality due to trap charging at the metal/semiconductor surface. The combination of these two memristive effects into multiterminal metal-oxide-semiconductor field-effect transistor (MOSFET) devices gives rise to new opportunities for both memory and logic applications as well as new sensors based on the physical mechanism that originate memristance. In the special case of four-terminal memristive Si nanowire devices, which are presented for the first time in this paper, enhanced functionality is demonstrated. Finally, the multiterminal memristive devices presented here have the potential of a very high integration density, and they are suitable for hybrid complementary metal-oxide-semiconductor (CMOS) cofabrication with a CMOS-compatible process.

Remote Doping and Schottky Barrier Formation in Strongly Quantum Confined Single PbSe Nanowire Field-Effect Transistors

We report studies of charge injection and transport in ambipolar, predominantly n-type, and unipolar p-type single, strongly quantum confined PbSe nanowire (NW) field effect transistors (FETs). The PbSe NW FETs operate as Schottky barrier FETs in which the Fermi level is pinned near midgap, consistent with the low ionicity of PbSe, and is nearly invariant with semiconductor doping. Electron and hole mobilities increase monotonically with decreasing temperature, dominated at high temperature by electron-phonon scattering with no evidence of scattering at low temperatures. Transport in NWs is consistent with their single crystalline nature. Surface oxygen used to dope the NWs acts remotely, providing a promising route to dope nanostructures.

Quantification of surface state effects in GaAs MESFETs

The operation of gallium arsenide schottky barrier field effect transistor is greatly affected by several anomalies such as frequency dispersion of output impedance, Zds; this low frequency behaviour is related to the presence of capture centres at the channel/substrate interface. In this context, we investigate the influence of such defects via a circuit consisting of a capacitance in series with a resistance placed in parallel to the output of a transistor, between drain and source. Then, using PSPICE program we made some simulations at several bias of the device and different values of elements characterising traps. It was found that the dispersion increases when the value of the drain bias increases. It was also shown that the dispersion increases with increasing trap resistance. Whereas, the trap capacitance greatly affects the initial and final saturation of the output impedance

Multiscale modeling of nanowire-based Schottky-barrier field-effect transistors for sensorapplications

We present a theoretical framework for the calculation of charge transport throughnanowire-based Schottky-barrier field-effect transistors that is conceptually simple but stillcaptures the relevant physical mechanisms of the transport process. Our approach combinestwo approaches on different length scales: (1) the finite element method is used to modelrealistic device geometries and to calculate the electrostatic potential across the Schottkybarrier by solving the Poisson equation, and (2) the Landauer–Büttiker approach combinedwith the method of non-equilibrium Green’s functions is employed to calculate thecharge transport through the device. Our model correctly reproduces typicalI–V characteristics of field-effect transistors, and the dependence of the saturated drain currenton the gate field and the device geometry are in good agreement with experiments. Ourapproach is suitable for one-dimensional Schottky-barrier field-effect transistors of arbitrarydevice geometry and it is intended to be a simulation platform for the development ofnanowire-based sensors.

Hydrogen Sensing with Diameter- and Chirality-Sorted Carbon Nanotubes

The work function of palladium is known to be sensitive to hydrogen by the formation of a surface dipole layer or Pd hydride. One approach to detect such a change in the work function can be based on the formation of a Schottky barrier between the palladium metal and a semiconductor. Here, we study the hydrogen sensitivity of Schottky barrier field-effect transistors made for the first time from diameter- and chirality-sorted semiconducting single-walled carbon nanotubes (s-SWNTs) in contact with Pd electrodes. We observe an unrivaled 100-fold change in the on-state conductance at 100 ppm H2 compared to air for devices with s-SWNT and diameters between 1 and 1.6 nm. Hydrogen sensing is not observed for devices of Pd-contacted few-layer graphene (FLG), as expected due to the absence of a significant Schottky barrier. Unexpectedly, we observe also a vanishing sensitivity for small-diameter SWNTs. We explain this observation by changes in the nanotube work function caused by spillover and chemisorption of atomic hydrogen onto small-diameter nanotubes. We also observe that long-term sensing stability is only achieved if the gate voltage is inverted periodically. Under constant gate bias, the sensitivity reduces with time, which we relate to gate screening by accumulated charges in the substrate.

Remarks on theoretical modelling of spin-dependent electronic transport in carbon nanotubes and graphene

Abstract This contribution reports on charge and spin transport through graphene nanoribbons (GrNs) and carbon nanotubes (CNTs). The paper focuses on the giant magnetoresistance effect in these materials, and their potential usefulness for spintronic applications. As examples, the following devices are shortly discussed: GrNs in the ballistic transport regime, a CNT-based Schottky-barrier field effect transistor (CNT SB-FET), as well as CNT quantum dots in the Coulomb blockade limit.

Experimental demonstration of In0.53Ga0.47As field effect transistors with scalable nonalloyed source/drain contacts

We demonstrate the integration of a nonalloyed contact structure developed for III-V semiconductors to the source/drain of an In0.53Ga0.47As metal-oxide-semiconductor field effect transistor (MOSFET) with atomic layer deposition (ALD) Al2O3 high-κ dielectric. This nonalloyed contact utilizes single metals in combination with dielectric dipoles to tune the metal/semiconductor Femi level pinning toward the semiconductor’s band edge for minimal contact resistance and barrier height. The metal/III-V semiconductor effective barrier heights have been reduced by as much as 0.40 eV using SiN and 0.55 eV using Al2O3 dielectrics. With this InGaAs nMOSFET as a starting point, this contact can be applied to other III-V n-type MOSFETs, p-type MOSFETs, and Schottky Barrier field effect transistors.

Novel contact structures for high mobility channel materials

Abstract

Metal/III-V Schottky barrier height tuning for the design of nonalloyed III-V field-effect transistor source/drain contacts

In this work, we introduce a novel nonalloyed contact structure for n-GaAs and n-In0.53Ga0.47As by using single metals in combination with a thin dielectric to tune the effective metal/III-V work function toward the conduction band edge. We reduced the effective Schottky barrier height (ΦB,eff) of Al/GaAs from 0.75 to 0.17 eV through the use of a thin atomic layer deposition Al2O3. Barrier height reduction was verified for a variety of metals (Y, Er, Al, Ti, and W) through direct measurements and deduced from increased diode current and reduced contact resistance. Similar results were observed on n-In0.53Ga0.47As. Two possible underlying mechanisms are discussed: one based on the formation of a dielectric dipole and the other based on the blocking of metal induced gap states. This structure has applications as a nonalloyed low resistance ohmic contact for III-V metal-oxide-semiconductor field-effect transistors (MOSFETs) or high electron mobility transistors (HEMTs), and as a near zero barrier height contact for III-V Schottky barrier field-effect transistors or diodes.

Palladium/silicon nanowire Schottky barrier-based hydrogen sensors

This work presents the design, fabrication, and characterization of a hydrogen sensor based on a palladium/nanowire Schottky barrier field-effect transistor that operates at room temperature. The fabricated sensor consists of boron-doped silicon nanowire arrays that are contact printed on top of a SiO2/Si substrate with subsequently evaporated Pd contacts. The fabrication process is compatible with post-CMOS and plastic substrate integration as it can be completed at temperatures below 150 ◦ C with good yield and repeatability. The sensor can reliably and reversibly detect H2 concentrations in the range from 3 ppm to 5% and has a sensitivity of 6.9%/ppm at 1000 ppm. A response distinguishable from drift and noise is produced in less than 5 s for H2 concentrations over 1000 ppm and less than 30 s for concentrations over 100 ppm. The sensor settles to 90% of the final signal value in about 1 h at lower concentrations and less than 1 min at 10,000 ppm H2. Drift over an 87-h measurement period is below 5 ppm H2 concentration. © 2009 Elsevier B.V. All rights reserved.

Schottky Barrier Field Effect Transistors with a Strained Carbon Nanotube Channel

Schottky Barrier Field Effect Transistors with a Strained Carbon Nanotube Channel

Impact of Line-Edge Roughness on Double-Gate Schottky-Barrier Field-Effect Transistors

The impact of line-edge roughness (LER) on double-gate (DG) Schottky-barrier field-effect transistors (SBFETs) in the level of device and circuit was investigated by a statistical simulation. The LER sequence is statistically generated by a Fourier analysis of the power spectrum of the Gaussian autocorrelation function. The results show that SBFETs are more sensitive to the LER effect in the 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> region and less sensitive in the subthreshold region compared with DG FinFETs. The aggressive fluctuation of drive current can be attributed to the variation of tunneling barrier width. Lowering the Schottky-barrier height and increasing the silicon-body thickness can suppress the parameter fluctuations from the LER effect. The simulation also shows that a 6T SRAM cell consisting of SBFETs is more vulnerable to noise disturbance than its counterpart consisting of FinFETs, particularly for the read operation, which is due to a larger mismatch of drivability of SBFETs within the cell.

Procedure for calculating microwave-amplifier matching circuits

A procedure for calculating the parameters of matching circuits in the case of complex-valued impedances of the generator and the load has been developed. The procedure has been tested by calculating the parameters of a microwave amplifier based on a Schottky-barrier field-effect transistor and by measuring the amplifier’s characteristics. The test results are presented.

Biomolecule detection using a silicon nanoribbon: accumulation mode versus inversionmode

Silicon nanoribbons were fabricated using standard optical lithography from silicon oninsulator material with top silicon layer thicknesses of 100, 60 and 45 nm. Electrically thesework as Schottky-barrier field-effect transistors and, depending on the substrate voltage,electron or hole injection is possible. The current through the nanoribbon is extremelysensitive to charge changes at the oxidized top surface and can be used for biomoleculedetection in a liquid. We show that for detection of streptavidin molecules theresponse is larger in the accumulation mode than in the inversion mode, althoughnot leading to higher detection sensitivity due to increased noise. The effect isattributed to the location in depth of the conducting channel, which for holes is closerto the screened surface charges of the biomolecules. Furthermore, the responseincreases for decreasing silicon thickness in both the accumulation mode and theinversion mode. The results are verified qualitatively and quantitatively through atwo-dimensional simulation model on a cross section along the nanoribbon device.

Schottky-barrier double-walled carbon-nanotube field-effect transistors

We investigate electronic transport properties of Schottky-barrier field-effect transistors (FETs) based on double-walled carbon nanotubes (DWCNTs) with a semiconducting outer shell and a metallic inner one. This kind of DWCNT-FETs shows asymmetries of the $I\text{\ensuremath{-}}V$ characteristics and threshold voltages due to the electron-hole asymmetry of the Schottky barrier. The presence of the metallic inner shell induces a large effective band gap, which is one order of magnitude larger than that due to the semiconducting shell alone of a single-walled carbon-nanotube FET.

Understanding Coulomb Effects in Nanoscale Schottky-Barrier-FETs

We employ a novel multiconfigurational self-consistent Green's function approach (MCSCG) for the simulation of nanoscale Schottky-barrier-field-effect transistors (SB-FETs). This approach allows the calculation of electronic transport with a seamless transition from the single-electron regime to room-temperature FET operation. The particular improvement of the MCSCG stems from a self-consistent division of the channel system into a small subsystem of resonantly trapped states for which a many-body Fock space approach becomes numerically feasible and the rest of the system which can be treated adequately on a conventional mean-field level. The Fock space description allows for the calculation of few-electron Coulomb charging effects beyond the mean-field. We compare a conventional Hartree nonequilibrium Green's function calculation with the results of the MCSCG approach. Using the MCSCG method, Coulomb blockade effects are demonstrated at low temperatures while, under strong nonequilibrium and high-temperature conditions, the Hartree approximation is retained. Finally, the visibility of quantum and single-electron effects in scaled transistor structures is discussed