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This paper reports the radio frequency (RF) and linearity performance of transistors using high-purity semiconducting carbon nanotubes. High-density, uniform semiconducting nanotube networks are deposited at wafer scale using our APTES-assisted nanotube deposition technique, and RF transistors with channel lengths down to 500 nm are fabricated. We report on transistors exhibiting a cutoff frequency (f(t)) of 5 GHz and with maximum oscillation frequency (f(max)) of 1.5 GHz. Besides the cutoff frequency, the other important figure of merit for the RF transistors is the device linearity. For the first time, we report carbon nanotube RF transistor linearity metrics up to 1 GHz. Without the use of active probes to provide the high impedance termination, the measurement bandwidth is therefore not limited, and the linearity measurements can be conducted at the frequencies where the transistors are intended to be operating. We conclude that semiconducting nanotube-based transistors are potentially promising building blocks for highly linear RF electronics and circuit applications.

Graphene has attracted considerable interest as a potential new electronic material1–11. With the highest carrier mobility exceeding 200,000 cm2/V·s, graphene is of particular interest for ultra-high speed radio frequency (RF) electronics12–18. However, the conventional dielectric integration and device fabrication processes cannot be readily applied to fabricate high speed graphene transistors because they can often introduce significant defects into the monolayer of carbon lattices and severely degrade the device performance19–21. Here we report a new approach to fabricate high-speed graphene transistors with a self-aligned nanowire gate to enable unprecedented performance. The graphene transistors are fabricated using a Co2Si/Al2O3 core/shell nanowire as the gate, with the source and drain electrodes defined through a self-alignment process and the channel length defined by the nanowire diameter. The physical assembly of nanowire gate preserves the high carrier mobility in graphene, and the self-aligned process ensures that the edges of the source, drain, and gate electrodes are automatically and precisely positioned so that no overlapping or significant gaps exist between these electrodes and thus minimizes access resistance. It therefore enables transistor performance not previously possible. Graphene transistors with channel length down to 140 nm have been fabricated with the highest scaled on-current (3.32 mA μm−1) and transconductance (1.27 mS μm−1) reported to date. Significantly, on-chip microwave measurements demonstrate that the self-aligned devices exhibit a record high intrinsic cutoff frequency (fT) in the range of 100–300 GHz, with the extrinsic fT in the range of a few gigahertz largely limited by parasitic pad capacitance. The reported intrinsic cutoff frequency of the graphene transistors is comparable to that of the very best high electron mobility transistors with similar gate lengths10. It therefore marks an important milestone in graphene RF devices and can enable exciting opportunities in high-speed electronics.

We describe and analyze a cellular nonlinear network based on magnetic nanostructures for image processing. The network consists of magneto-electric cells integrated onto a common ferromagnetic film–spin wave bus. The magneto-electric cell is an artificial two-phase multiferroic structure comprising piezoelectric and ferromagnetic materials. A bit of information is assigned to the cell’s magnetic polarization, which can be controlled by the applied voltage. The information exchange among the cells is via the spin waves propagating in the spin wave bus. Each cell changes its state as a combined effect: magneto-electric coupling and the interaction with the spin waves. The distinct feature of a network with a spin wave bus is the ability to control the inter-cell communication by an external global parameter — magnetic field. The latter makes it possible to realize different image processing functions on the same template without rewiring or reconfiguration. We present the results of numerical simulations illustrating image filtering, erosion, dilation, horizontal and vertical line detection, inversion and edge detection accomplished on one template by the proper choice of the strength and direction of the external magnetic field. We also present numerical assets on the major network parameters such as cell density, power dissipation and functional throughput, and compare them with the parameters projected for other nano-architectures such as CMOL-CrossNet, Quantum-Dot Cellular Automata, and Quantum Dot-Image Processor. Potentially, the utilization of spin wave phenomena at the nanometer scale may provide a route to low-power consumption and functional logic circuits for special task data processing.

We propose and describe a magnetic NanoFabric which provides a route to building reconfigurable spin-based logic circuits compatible with conventional electron-based devices. A distinctive feature of the proposed NanoFabric is that a bit of information is encoded into the phase of the spin wave signal. It makes possible to transmit information without the use of electric current and utilize wave interference for useful logic functionality. The basic elements include voltage-to-spin wave and wave-to-voltage converters, spin waveguides, a modulator, and a magnetoelectric cell. As an example of a magnetoelectric cell, we consider a two-phase piezoelectric-piezomagnetic system, where the spin wave signal modulation is due to the stress-induced anisotropy caused by the applied electric field. The performance of the basic elements is illustrated by experimental data and results of numerical modeling. The combination of the basic elements let us construct magnetic circuits for NOT and Majority logic gates. Logic gates AND, OR, NAND and NOR are shown to be constructed as the combination of NOT and a reconfigurable Majority gates. The examples of computational architectures such as Cellular Automata, Cellular Nonlinear Network and Field Programmable Gate Array are described. The main advantage of the proposed NanoFabric is in the ability to realize logic gates with less number of devices than it required for CMOS-based circuits. Potentially, the area of the elementary reconfigurable Majority gate can be scaled down to 0.1um2. The disadvantages and limitations of the proposed NanoFabric are discussed.

We describe a new approach to logic devices interconnection by the inductive coupling via a ferromagnetic film. The information among the distant devices is transmitted in a wireless manner via a magnetic field produced by spin waves propagating in the ferromagnetic film, referred to as the spin wave bus. As an alternative approach to the transistor-based architecture, logic circuits with spin wave bus do not use charge as an information carrier. A bit of information can be encoded into the phase or the amplitude of the spin wave signal. We present experimental data demonstrating inductive coupling through the 100 nm thick NiFe and CoFe films at room temperature. The performance of logic circuits with spin wave bus is illustrated by numerical modeling based on the experimental data. Potentially, logic circuits with spin wave bus may resolve the interconnect problem and provide "wireless" read-in and read-out. Another expected benefit is in the enhanced logic functionality. A set of "NOT," "AND," and "OR" logic gates can be realized in one device structure. The coupling between the circuits and the spin wave bus can be controlled. We present the results of numerical simulations showing the controllable switching of a bi-stable logic cell inductively coupled to the spin wave bus. The shortcomings and limitations of circuits with spin wave bus are also discussed.

This paper provides an approach to monitor oscillation status in tunnel diode measurement circuits-by,measuring the second derivative of the current-voltage (I-V) characteristic curve while doing I-V curve measurement. The method of using the second derivative to detect oscillations works even when the oscillation frequency is ultrahigh or the oscillation amplitude is very small, e.g., below 10 mV. In this paper, the experimental principle of the tunneling spectroscopy was extended to measurement circuits with the presence of internal oscillations, in contrast to the conventional tunneling spectroscopy, which normally does not deal with internal oscillation. The numerical relationships between the measured average values of transient derivatives and the derivatives of the average current are derived: The average values of the transient first and second derivatives are shown to equal the derivatives of the average current. These relationships serve as the foundation for the authors' experiments. The typical oscillation characteristics in the curves of the first and the second derivatives are used to detect the presence of oscillations and the bias voltage range of oscillation in the I-V curve. The monitor of oscillation status during measurements provides the tester the confidence in the measurement data and whether it is necessary to improve the test circuit further. Finally, benefited from free-of-oscillation, the indirect tunneling current contributions arising by 121-mV (TO + 0) two-phonon combination, 144-mV (TA + 0 + 0) and 181-mV (TO + 0 + 0) three-phonon combinations at the negative differential resistance region are observed from a silicon Esaki tunnel diode at 4.2 K.

Drain leakage current in accumulated metal–oxide–semiconductor field-effect transistors (MOSFETs) is pumped out completely by the body, while the source current should be zero due to the barrier of the p/n junction between the source and the accumulated channel. In this letter, we observe a fraction of drain current flowing into the source terminal in accumulated p-channel MOSFETs at low temperature. Under a certain gate bias region, the random telegraph noise (RTN) with an amplitude of 30% is observed in the source current of the devices. The source-current RTN disappears completely when the measured temperature exceeds 4.2 K. The source-current RTN is strongly affected by applied magnetic field, which causes the large decrease of the average switching time of the source RTN. We believe that the random charging and discharging of single defects at the SiO2/Si interface of the gate–source overlap region may strongly disturb the band-to-band tunneling process, and thereby result in the source-current RTN.

We describe and analyze a magnetic cellular nonlinear network using spin waves for information exchange. The network consists of magneto-electric cells integrated onto a common ferromagnetic film-spin wave bus. A magneto-electric cell is an artificial multiferroic comprising piezomagnetic and piezoelectric materials, which electric and magnetic polarizations entangled via the magneto-electric coupling. A bit of information is encoded into the cell's magnetic polarization, which is controlled by the applied electric field. The cell interacts with other cells not directly but via the spin waves propagating in the spin wave bus. The latter makes it possible to control the intercell communication by an external global parameter-magnetic field. We present the results of numerical modeling illustrating network performance. The utilization of spin waves offers an intrigue possibility to exploit wave phenomena at nanometer scale for building low-power dissipating and multi-functional logic devices for special task data processing. The disadvantages and shortcomings of the magnetic network with spin wave bus are also discussed.

Spin-wave based devices [1, 2] have been shown to be promising for parallel data processing at high speed. However, no gain with current spin-wave de vice and large dam ping of spin-wave signals lim it their application, especially in cascaded signal processing. In this talk, we re port a prototype spin-wave amplifier with a power gain controlled by a pump power input.

We demonstrate a three-terminal spin wave-based device utilizing spin wave interference. The device consists of three coplanar transmission lines inductively coupled to the 100 nm thick CoFe film. Two spin wave signals are excited by microwave fields produced by electric current in two sets of lines, and the output signal is detected by the third set. The initial phases of the spin wave signals are controlled by the direction of the current flow in the excitation set of lines. Experimental data show prominent output signal modulation as a function of the relative phase (in-phase and out-of phase) of two input signals. The micrometer scale device operates in the GHz frequency range and at room temperature. Our experimental results show that spin-wave devices exploiting spin wave interference may be scaled to micrometer and nanometer scales for potential logic circuit application.

It is well recognized that novel computational models, devices and technologies are needed in order to sustain the remarkable advancement of CMOS-based VLSI circuits and systems. Regardless of the models, devices and technologies, any enhancement/replacement to CMOS must show significant gains in at least one of the key metrics (including speed, power and cost) for at least a subset of application domains currently employing CMOS circuits. In addition, effective defect tolerant techniques are a critical factor for the successful adoption of any new computing device due to the fact that nano-scale structures will have defect rates much higher than today's CMOS chips. The task of identifying application domains that could benefit the most from a new model/device/technology and ensuring that the resultant system meets functional requirements in the presence of defects requires synergistic efforts of physical scientists, and circuit and system design researchers.This paper contains a collection of three contributions-each focusing on one particular emergent technology-presenting a basic introduction on the technologies, some of their unique features in contrast with CMOS, potential application domains for these technologies, and new opportunities that they may bring forward in defect tolerance design. The contributions include both traditional and nontraditional state representations which use either electronic or magnetic interactions.

We have designed and fabricated a coplanar waveguide ferromagnetic parametric amplifier based on ferromagnetic alloy cobalt-iron (CoFe) thin film. The ferromagnetic parametric amplifier has the gain of 4 dB at 1.15 GHz. To our knowledge, it is the first coplanar waveguide ferromagnetic parametric amplifier operating at radio frequency reported to date, and we haven't found an item from Google search by keying in words "coplanar 'ferromagnetic parametric amplifier'" or "coplanar 'magnetic parametric amplifier".

The authors analyze the performance and estimate the efficiency of the spin-wave based logic devices. The main potential advantage of using spin wave for information transmission and processing is that a bit of information can be transmitted without use of an electric current. Spin-wave based devices may find an application as an interface between the electronic and magnetic circuits. The authors show the schematics of the integration of the spin-wave based devices with conventional electron-based circuit. The input information is received in the form of voltage pulses. Next, it is converted into the spin wave signals, where logic state 1 and 0 corresponds to the phases of the spin waves. Spin-wave based device accomplishes computation using spin wave signals and provides the output on the form of voltage pulses.

We analyze spin wave-based logic circuits for information transmission and processing in integrated magneto-electric circuits. A bit of information is encoded into the phase of the spin wave propagating in the magnetic waveguide referred to as spin wave bus. It makes possible to transmit and process a number of bits at constant time. By exploiting sin wave superposition, a set of logic gates such as AND, OR, and Majority gate can be realized in one circuit. This paper presents the realization of a spin-wave based logic circuit fabricated on a silicon platform. The prototype micrometer scale circuit operates in the GHz frequency range and offers exciting potential as a multifunctional logic gate that could be scaled down to 0.1 mum2 with energy per bit as low as 10-18 J. Another potential advantage of the spin wave-based logic circuitry is the ability to implement logic gates with fewer elements as compared to CMOS- based circuits in achieving same functionality. The shortcomings and disadvantages of the spin wave-based devices are discussed.

We analyze spin wave-based logic circuits as a possible route to building reconfigurable magnetic circuits compatible with conventional electron-based devices. A distinctive feature of the spin wave logic circuits is that a bit of information is encoded into the phase of the spin wave. It makes possible to transmit information as a magnetization signal through magnetic waveguides without the use of an electric current. By exploiting sin wave superposition, a set of logic gates such as AND, OR, and Majority gate can be realized in one circuit. We present experimental data illustrating the performance of a three-terminal micrometer scale spin wave-based logic device fabricated on a silicon platform. The device operates in the GHz frequency range and at room temperature. The output power modulation is achieved via the control of the relative phases of two input spin wave signals. The obtained data shows the possibility of using spin waves for achieving logic functionality. The scalability of the spin wave-based logic devices is defined by the wavelength of the spin wave, which depends on the magnetic material and waveguide geometry. Potentially, a multifunctional spin wave logic gate can be scaled down to 0.1μm2. Another potential advantage of the spin wave-based logic circuitry is the ability to implement logic gates with fewer elements as compared to CMOS-based circuits in achieving same functionality. The shortcomings and disadvantages of the spin wave-based devices are also discussed.

We investigate spin wave propagation and interference in conducting ferromagnetic nanostructures for potential application in spin wave based logic circuits. The novelty of this approach is that information transmission is accomplished without charge transfer. A bit of information is encoded into the phase of spin wave propagating in a nanometer thick ferromagnetic film. A set of “AND”, “NOR”, and “NOT” logic gates can be realized in one device structure by utilizing the effect of spin wave superposition. We present experimental data on spin wave transport in 100nm CoFe films at room temperature obtained by the propagation spin wave spectroscopy technique. Spin wave transport has been studied in the frequency range from 0.5 GHz to 6.0 GHz under different configurations of the external magnetic field. Both phase and amplitude of the spin wave signal are sensitive to the external magnetic field showing 60Deg/10G and 4dB/20G modulation rates, respectively. Potentially, spin wave based logic circuits may compete with traditional electron-based ones in terms of logic functionality and power consumption. The shortcomings of the spin wave based circuits are discussed.

We present a feasibility study of logic circuits utilizing spin waves for information transmission and processing. As an alternative approach to the transistor-based architecture, logic circuits with a spin wave bus do not use charge as an information carrier. In this work we describe the general concept of logic circuits with a spin wave bus and illustrate its performance by numerical simulations based on available experimental data. Theoretical estimates and results of numerical simulations on signal attenuation, signal phase velocity, and the minimum spin wave energy required per bit in the spin bus are obtained. The transport parameters are compared with ones for conventional electronic transmission lines. The spin wave bus is not intended to substitute traditional metal interconnects since it has higher signal attenuation and lower signal propagation speed. The potential value of a spin wave bus is, however, an interface between electronic circuits and integrated spintronics circuits. The logic circuits with a spin wave bus allow us to provide wireless read-in and read-out.

An analytical expression for the amplitudes of magnetostatic surface spin waves (MSSWs) propagating in opposite directions at a magnetic film surface is presented. This shows that for a given magnetic field H, it is forbidden for an independent MSSW to propagate along the direction of − H→×n→, where n→ is the surface normal. This unidirectional propagation property is confirmed by experiments with both permalloy and yttrium iron garnet films of different film thicknesses, and has implications in the design of spin-wave devices such as isolators and spin-wave diodes.

The ambipolar random telegraph signal (RTS) (i.e., RTS in both hole conduction at negative gate biases and electron conduction at positive gate biases) is observed in an ambipolar carbon nanotube field-effect transistor (CNT-FET). Then, the ambipolar RTS is used to extract the small band gap of the SWNT. The determination of the small band gap CNT using RTS demonstrates a potentially high accuracy and stability. Other methods are provided to confirm the small band gap of the SWNT.

In this work, we report on the demonstration of voltage-driven spin wave excitation, where spin waves are generated by multiferroic magnetoelectric (ME) cell transducers driven by an alternating voltage, rather than an electric current. A multiferroic element consisting of a magnetostrictive Ni film and a piezoelectric [Pb(Mg1/3Nb2/3)O3](1−x)–[PbTiO3]x substrate was used for this purpose. By applying an AC voltage to the piezoelectric, an oscillating electric field is created within the piezoelectric material, which results in an alternating strain-induced magnetic anisotropy in the magnetostrictive Ni layer. The resulting anisotropy-driven magnetization oscillations propagate in the form of spin waves along a 5 μm wide Ni/NiFe waveguide. Control experiments confirm the strain-mediated origin of the spin wave excitation. The voltage-driven spin wave excitation, demonstrated in this work, can potentially be used for low-dissipation spin wave-based logic and memory elements.

The utilization of a magnetoelectric film composite to control, by an electric field, the phase of magnetostatic surface spin waves propagating along thin films is reported. Laminates of ferromagnetic films of Ni and NiFe are deposited on a ferroelectric substrate, lead magnesium niobate-lead titanate. The phase of propagating spinwaves is shown to be modulated by an electric field while traveling a finite distance along the surface. The observed phase change in the spinwaves is in agreement with the anisotropy field changes measured with magneto optical Kerr effect hysteresis loops. A quantitative agreement is demonstrated.

Electrical control of the dielectric constant in (011) [Pb(Mg1/3Nb2/3)O3](1−x)-[PbTiO3]x (PMN-PT, x ≈ 0.32) single crystal ferroelectric material is reported. It is demonstrated that the metastable dielectric constant value of (011) PMN-PT can be manipulated from approximately 3000 to 1000 by applying electric pulses of different amplitudes. These metastable properties are due to non-180° polarization reorientation within the ferroelectric crystals. Taking advantage of the tunable and metastable dielectric constant, a reconfigurable RC oscillator as well as a ferroelectric memory device is demonstrated. The reconfigurability of this ferroelectric capacitor and potential applications for low-power electronics are described.

The ferroelectric properties of (011) [Pb(Mg1/3Nb2/3)O3](1−x)-[PbTiO3]x (PMN-PT, x≈0.32) single crystals with focus on piezoelectric strain response were reported. Two giant reversible and stable remanent strain states and tunable remanent strain properties are achieved by properly reversing the electric field from the depolarized direction. The unique piezoelectric strain response, especially along the [100] direction, mainly stems from the non-180° ferroelectric polarization reorientation in the rhombohedral phase crystal structure. Such giant strain hysteresis with tunable remanent strain properties may be useful for magnetoelectric based memory devices as well as a potential candidate for other applications.

We describe and analyse possible approaches to magnonic logic circuits and basic elements required for circuit construction. A distinctive feature of the magnonic circuitry is that information is transmitted by spin waves propagating in the magnetic waveguides without the use of electric current. The latter makes it possible to exploit spin wave phenomena for more efficient data transfer and enhanced logic functionality. We describe possible schemes for general computing and special task data processing. The functional throughput of the magnonic logic gates is estimated and compared with the conventional transistor-based approach. Magnonic logic circuits allow scaling down to the deep submicrometre range and THz frequency operation. The scaling is in favour of the magnonic circuits offering a significant functional advantage over the traditional approach. The disadvantages and problems of the spin wave devices are also discussed.

Even though the strong Fermi-level pinning at the metal/germanium (Ge) interface can be alleviated by inserting a thin layer of tunneling oxide, the still sizeable Schottky barriers and the wide depletion regions of the Fe/oxide/n-Ge contacts make the junction resistances strongly dependent of temperature. The resistance-area (RA) products of these junctions are too high for spin injection and cannot be tuned by simply varying oxide thickness or using ferromagnetic metal (FM) with a lower work function. In this work, low energy ion implantation and rapid thermal annealing were utilized to degenerately dope the Ge surface layer to facilitate single-step tunneling transport. The RA products of the junctions with surface doping are significantly reduced and weakly dependent of temperature. This method gives a prospect for spin injection to Ge from FM.

Different to conventional ferromagnetic resonance methods, we use the phase-shift of spin-wave propagation to investigate spin-wave in conducting ferromagnetic thin films. Spin-wave wave vector (or wave number) k, a key parameter in the study of spin-wave dispersion and propagation, is extracted from the ratio of the phase-shift to the propagation distance and the ratio of the intercepts to the slopes of the plot of frequency square (f2) vs. the bias field (H). The wave vectors calculated by both methods are in good agreement. The in-plane anisotropy field Hk and saturation magnetization MS can also be extracted from the phase-shift map.

Electron tunneling spectroscopy is used to study drain-source current spectra of metal-oxide-semiconductor field-effect transistors (MOSFETs). Measured at liquid helium temperature (4.2 K), experimental results reveal that as drain-source voltage (V-ds) increases, the first derivative of drain-source current (or conductance) first decreases, then increases to a maximum and finally decreases again at higher Vds, which is different from the monotonous decreasing feature described by the conventional MOSFET theory. In addition, the measured MOSFET spectra show that there are fine features on the second derivative spectra, and these features may be used to extract trap information. (c) 2005 American Institute of Physics.

The gate-dependent one-dimensional transport of single-crystal In2O3 nanowire field effect transistors is studied at low temperature by measuring current (I-V) and differential conductance (dIds∕dVds). At a smaller positive gate bias, gaps at near-zero source-drain bias were observed for both current and differential conductance spectra due to the absence of the density of states in the source-drain energy window for a small Vds. The transport can be explained using conventional low-temperature field effect transistor theory. On the other hand, at a large gate bias when the Fermi energy of the nanowire moves up into its conduction band, the differential conductance of the semiconducting In2O3 nanowire exhibits zero-bias anomalies, following a power-law behavior.

Giant random telegraph signals (RTSs) are observed in p-type semiconducting single-wall carbon nanotube (SWNT) field-effect transistors (FETs). The RTSs are attributed to the trapping and detrapping of the two defects inside SiO2 or in the interface between SWNT and SiO2. The amplitude of the RTSs is up to 60% of total current. The giant switching amplitude of RTSs is believed to be caused by the strong mobility modulation originated from the charging of the defects in the one-dimensional carbon nanotube channels with an ultrasmall channel width on the order of 1–3 nm. The potential application of RTSs in SWNT as a sensitive probe to study single defects is discussed.