Showing papers on "Nanoelectronics published in 2002"

Growth of nanowire superlattice structures for nanoscale photonics and electronics.

Abstract: The assembly of semiconductor nanowires and carbon nanotubes into nanoscale devices and circuits could enable diverse applications in nanoelectronics and photonics1. Individual semiconducting nanowires have already been configured as field-effect transistors2, photodetectors3 and bio/chemical sensors4. More sophisticated light-emitting diodes5 (LEDs) and complementary and diode logic6,7,8 devices have been realized using both n- and p-type semiconducting nanowires or nanotubes. The n- and p-type materials have been incorporated in these latter devices either by crossing p- and n-type nanowires2,5,6,9 or by lithographically defining distinct p- and n-type regions in nanotubes8,10, although both strategies limit device complexity. In the planar semiconductor industry, intricate n- and p-type and more generally compositionally modulated (that is, superlattice) structures are used to enable versatile electronic and photonic functions. Here we demonstrate the synthesis of semiconductor nanowire superlattices from group III–V and group IV materials. (The superlattices are created within the nanowires by repeated modulation of the vapour-phase semiconductor reactants during growth of the wires.) Compositionally modulated superlattices consisting of 2 to 21 layers of GaAs and GaP have been prepared. Furthermore, n-Si/p-Si and n-InP/p-InP modulation doped nanowires have been synthesized. Single-nanowire photoluminescence, electrical transport and electroluminescence measurements show the unique photonic and electronic properties of these nanowire superlattices, and suggest potential applications ranging from nano-barcodes to polarized nanoscale LEDs.

Single-walled carbon nanotube electronics

Abstract: Single-walled carbon nanotubes (SWNTs) have emerged as a very promising new class of electronic materials. The fabrication and electronic properties of devices based on individual SWNTs are reviewed. Both metallic and semiconducting SWNTs are found to possess electrical characteristics that compare favorably to the best electronic materials available. Manufacturability issues, however, remain a major challenge.

Defects in carbon nanotubes.

Abstract: Carbon nanotubes are quasi one-dimensional nanostructures with unique eletrical prroperties that make them prime candidates for molecular electronics, which is certainly a most promising direction in nanotechnology. Early theoretical works predicted that the electronic properties of "ideal" carbon nanotubes depend on their diameter and chirality. However, carbon nanotubes are probably not as perfect as they were once thought to be. Defects such as pentagons, heptagons, vacancies, or dopant are found to modify drastically the electronic properties of these nanosystems. Irradiation processes can lead to interesting, highly defective nanostructures and also to the coalescence of nanotubes within a rope. The introduction of defects in the carbon network is thus an interesting way to tailor its intrinsic properties, to create new potential nanodevices. The aim of the present Acount is to investigate theoretically the effects of different types of defects on the electronic properties of carbon nanotubes, and to propose new potential applications in nanoelectronics.

Luttinger liquid theory as a model of the gigahertz electrical properties of carbon nanotubes

Abstract: Presents a technique to directly excite Luttinger liquid collective modes in carbon nanotubes at gigahertz frequencies. By modeling the nanotube as a nano-transmission line with distributed kinetic and magnetic inductance as well as distributed quantum and electrostatic capacitance, we calculate the complex frequency-dependent impedance for a variety of measurement geometries. Exciting voltage waves on the nano-transmission line is equivalent to directly exciting the yet-to-be observed one-dimensional plasmons, the low energy excitation of a Luttinger liquid. Our technique has already been applied to two-dimensional plasmons and should work well for one-dimensional plasmons. Tubes of length 100 microns must be grown for gigahertz resonance frequencies. Ohmic contact is not necessary with our technique; capacitive contacts can work. Our modeling has applications in potentially terahertz nanotube transistors and RF nanospintronics.

FinFET scaling to 10 nm gate length

Abstract: While the selection of new "backbone" device structure in the era of post-planar CMOS is open to a few candidates, FinFET and its variants show great potential in scalability and manufacturability for nanoscale CMOS In this paper we report the design, fabrication, performance, and integration issues of double-gate FinFETs with the physical gate length being aggressively shrunk down to 10 nm and the fin width down to 12 nm These MOSFETs are believed to be the smallest double-gate transistors ever fabricated Excellent short-channel performance is observed in devices with a wide range of gate lengths (10/spl sim/105 nm) The observed short-channel behavior outperforms any reported single-gate silicon MOSFETs Due to the [110] channel crystal orientation, hole mobility in the fabricated p-channel FinFET exceeds greatly that in a traditional planar MOSFET At 105 nm gate length, the p-channel FinFET shows a record-high transconductance of 633 /spl mu/S//spl mu/m at a V/sub dd/ of 12 V Working CMOS FinFET inverters are also demonstrated

Simulating quantum transport in nanoscale transistors: Real versus mode-space approaches

Abstract: In this article, we present a computationally efficient, two-dimensional quantum mechanical simulation scheme for modeling electron transport in thin body, fully depleted, n-channel, silicon-on-insulator transistors in the ballistic limit. The proposed simulation scheme, which solves the nonequilibrium Green’s function equations self-consistently with Poisson’s equation, is based on an expansion of the active device Hamiltonian in decoupled mode space. Simulation results from this method are benchmarked against solutions from a rigorous two-dimensional discretization of the device Hamiltonian in real space. While doing so, the inherent approximations, regime of validity and the computational efficiency of the mode-space solution are highlighted and discussed. Additionally, quantum boundary conditions are rigorously derived and the effects of strong off-equilibrium transport are examined. This article shows that the decoupled mode-space solution is an efficient and accurate simulation method for modeling e...

Nanowire resonant tunneling diodes

Abstract: Semiconductor heterostructures and their implementation into electronic and photonic devices have had tremendous impact on science and technology. In the development of quantum nanoelectronics, one-dimensional (1D) heterostructure devices are receiving a lot of interest. We report here functional 1D resonant tunneling diodes obtained via bottom-up assembly of designed segments of different semiconductor materials in III/V nanowires. The emitter, collector, and the central quantum dot are made from InAs and the barrier material from InP. Ideal resonant tunneling behavior, with peak-to-valley ratios of up to 50:1 and current densities of 1 nA/μm2 was observed at low temperatures.

Carbon nanotube electronics

Abstract: Presents experimental results on single-wall carbon nanotube field-effect transistors (CNFETs) operating at gate and drain voltages below 1V. Taking into account the extremely small diameter of the semiconducting tubes used as active components, electrical characteristics are comparable with state-of-the-art metal oxide semiconductor field-effect transistors (MOSFETs). While output as well as subthreshold characteristics resemble those of conventional MOSFETs, we find that CNFET operation is actually controlled by Schottky barriers (SBs) in the source and drain region instead of by the nanotube itself. Due to the small size of the contact region between the electrode and the nanotube, these barriers can be extremely thin, enabling good performance of SB-CNFETs.

Fabrication and electrical characteristics of carbon nanotube field emission microcathodes with an integrated gate electrode

Abstract: We report on the fabrication of field emission microcathodes which use carbon nanotubes as the field emission source. The devices incorporated an integrated gate electrode in order to achieve truly low-voltage field emission. A single-mask, self-aligned technique was used to pattern the gate, insulator and catalyst for nanotube growth. Vertically-aligned carbon nanotubes were then grown inside the gated structure by plasma-enhanced chemical vapour deposition. Our self-aligned fabrication process ensured that the nanotubes were always centred with respect to the gate apertures (2 µm diameter) over the entire device. In order to obtain reproducible emission characteristics and to avoid degradation of the device, it was necessary to operate the gate in a pulsed voltage mode with a low duty cycle. The field emission device exhibited an initial turn-on voltage of 9 V. After the first measurements, the turn-on voltage shifted to 15 V, and a peak current density of 0.6 mA cm-2 at 40 V was achieved, using a duty cycle of 0.5%.

Nanotechnology: Basic Science and Emerging Technologies

Abstract: BACKGROUND TO NANOTECHNOLOGY Scientific Revolutions Types of Nanotechnology and Nanomachines The Periodic Table Atomic Structure Molecules and Phases Energy Molecular and Atomic Size Surfaces and Dimensional Space Top Down and Bottom Up MOLECULAR NANOTECHNOLOGY Atoms by Inference Electron Microscopes Scanning Electron Microscope Modern Transmission Electron Microscope Scanning Probe Microscopy - Atomic Force Microscope Scanning Tunnelling Microscope Nanomanipulator Nanotweezers Atom Manipulation Nanodots Self Assembly Dip Pen Nanolithography NANOPOWDERS AND NANOMATERIALS What Are Nanomaterials? Preparation Plasma Arcing Chemical Vapour Deposition Sol-Gels THE CARBON AGE New Forms of Carbon Types of Nanotubes Formation of Nanotubes Assemblies Purification of Carbon Nanotubes The Properties of Nanotubes Uses of Nanotubes MOLECULAR MIMICS Catenanes and Rotaxanes Molecular Switches The Electron Driven Molecular Shuttle Switch The pH Driven Molecular Shuttle Switch The Light Driven Molecular Shuttle Switch Synthesis of Rotaxanes and Catenanes Rotaxanes and Molecular Computers Chemical Rotors Prodders Flippers Atom Shuttles Actuators Contacts NANOBIOMIMETICS Introduction Lipids as Nano-Bricks and Mortar Same but Different: Self-Assembled Nanolayers The Bits that Do Things - Proteins Structure is Information - DNA A Biological Nanotechnological Future OPTICS, PHOTONICS AND SOLAR ENERGY Properties of Light and Nanotechnology Interaction of Light and Nanotechnology Nanoholes and Photons Imaging New low Cost Energy Efficient Windows and Solar Absorbers Based On Nanoparticles Photonic Crystals, Surface Wave Guides and Control of Light Paths NANOELECTRONICS Introduction What Will Nanoelectronics Do for Us? The Birth of Electronics The Tools of Micro- and Nanofabrication From Classical to Quantum Physics Quantum Electronic Devices Quantum Information and Quantum Computers Experimental Implementations of Quantum Computers FUTURE APPLICATIONS Micro-Electromechanical Machines Robots - How Small Can They Go? Ageless Materials Invisible Mending of Atomic Dislocations Inside Damaged Materials Nanomechanics and Nanoelasticity Nanoparticle Coatings - Special New Effects Nanoelectronic and Magnetic Devices and New Computing Systems Optoelectronic Devices Environmental Applications INTO THE REALMS OF IMAGINATION Introduction Communication Manufacturing Nanomedicine Society and Ethics Religion and Making Everything from Everything Else Thanks for All the Fish REFERENCES INDEX Each chapter also contains References and Exercises

Nanotechnology goals and challenges for electronic applications

Abstract: Si metal-oxide-semiconductor field-effect transistor (MOSFET) scaling trends are presented along with a description of today's 0.13-/spl mu/m generation transistors. Some of the foreseen limits to future scaling include increased subthreshold leakage, increased gate oxide leakage, increased transistor parameter variability and interconnect density and performance. Basic device and circuit requirements for electronic logic and memory products are described. These requirements need to be kept in mind when evaluating nanotechnology options such as carbon nanotube field-effect transistors (FETs), nanowire FETs, single electron transistors and molecular devices as possible future replacements for Si MOSFETs.

Crystalline Boron Nanowires

Abstract: Ideal nanowire interconnects for nanoelectronics will be refractory, covalently bonded, and highly conductive, irrespective of crystallographic orientation. Theoretical studies suggest that boron nanotubes should be stable and exhibit higher electrical conductivities than those of carbon nanotubes. We describe CVD growth of elemental boron nanowires, which are found to be dense nanowhiskers rather than nanotubes. Conductivity measurements establish that they are semiconducting, with electrical properties consistent with those of elemental boron. High conductivities should be achievable through doping.

Carbon nanotube field-effect transistors and logic circuits

Abstract: In this paper, we present recent advances in the understanding of the properties of semiconducting single wall carbon nanotube and in the exploration of their use as field-effect transistors (FETs). Both electrons and holes can be injected in a nanotube transistor by either controlling the metal-nanotube Schottky barriers present at the contacts or simply by doping the bulk of the nanotube. These methods give complementary nanotube FETs that can be integrated together to make inter- and intra-nanotube logic circuits. The device performance and their general characteristics suggest that they can compete with silicon MOSFETs. While this is true when considering simple prototype devices, several issues remain to be explored before a nanotube-based technology is possible. They are also discussed.

Carbon nanotubes from organometallic precursors.

Abstract: Multiwalled as well as single-walled carbon nanotubes are conveniently prepared by the pyrolysis of organometallic precursors such as metallocenes and phthalocyanines in a reducing atmosphere. More importantly, pyrolysis of organometallics alone or in mixture with hydrocarbons yields aligned nanotube bundles with useful field emission and hydrogen storage properties. By pyrolysis of organometallics in the presence of thiophene, Y-junction nanotubes are obtained in large quantities. The Y-junction tubes have a good potential in nanoelectronics. Carbon nanotubes prepared from organometallics are useful to prepare nanowires and nanotubes of other materials such as BN, GaN, SiC, and Si 3 N 4 .

Carbon nanotube devices for nanoelectronics

Abstract: We present a review of recent fundamental research on carbon nanotubes, with the goal of realizing future nanometer-scale electronic applications. Since nanotubes are by nature nanometer-scale devices with remarkable electrical properties, they are expected to be an important element in nanometer-scale electronics. As preliminary steps towards realizing nanotube-electronics, we have investigated the formation mechanism of metal contacts to carbon nanotubes, nanotube device fabrication possibilities, and nanotube spin electronics.

Carbon nanotube electronics

Abstract: We briefly review the electronic properties of carbon nanotubes (CNTs) and present results on the fabrication and characteristics of carbon nanotube field-effect transistors (CNTFETs) and simple integrated circuits. A novel approach allowing the catalyst-free synthesis of oriented CNTs is also presented.

Assessment of silicon MOS and carbon nanotube FET performance limits using a general theory of ballistic transistors

Abstract: A simple model for ballistic nanotransistors, which extends previous work by treating both the charge control and the quantum capacitance limits of MOSFET-like transistors, is presented. We apply this new model to MOSFET-like carbon nanotube FETs (CNTFETs) and to MOSFETs at the scaling limit. The device physics for operation at ballistic and quantum capacitance limits are explored. Based on the analysis of recently reported CNTFETs, we compare CNTFETs to MOSFETs. The potential performance advantages over Si that might be achieved at the scaling limit are established by using the new model.

Carbon nanotube transistors and logic circuits

Abstract: We discuss our recent efforts to develop high performance carbon nanotube field effect transistors (CNTFETs) and logic circuits. By improving the metal nanotube contacts the characteristics of the CNTFETs are greatly enhanced. Analysis shows that the performance of p-type CNTFETs is already competitive to that of silicon p-MOSFETs. In addition to the p-CNTFETs, we present techniques by which ambipolar and pure n-type CNTFETs can be fabricated. A particulary simple process involving the annealing in vacuum of a p-CNTFET is shown to convert it to an n-CNTFET. This conversion is reversible, and re-exposure to oxygen leads to a p-CNTFET. Evidence is found that the key effect of oxygen involves modification of the contact barriers. Having complementary CNTFETs (i.e. p- and n-type) allows us to build the first integrated circuits. We present results on a NOT logic gate. Both an inter-molecular gate involving two separate CNTFETs, and an intra-molecular gate where the logic function is encoded along the length of a single tube are demonstrated.

Design and analysis of crossbar circuits for molecular nanoelectronics

Abstract: We consider crossbar structures for nanoelectronics from a circuit design perspective. Given the large design space and the many promising nanotechnologies, we develop parameterized circuit models for quickly surveying the crossbar design space. We then present methods for implementing logic and memory in crossbars via a programmed decoder. Finally, we consider the implications of logic representation when mapping circuits to crossbars.

G-quartet biomolecular nanowires

Abstract: We present a first-principle investigation of quadruple helix nanowires, consisting of stacked planar hydrogen-bonded guanine tetramers. Our results show that long wires form and are stable in potassium-rich conditions. We present their electronic band structure and discuss the interpretation in terms of effective wide-band-gap semiconductors. The microscopic structural and electronic properties of the guanine quadruple helices make them suitable candidates for molecular nanoelectronics.

Few electron devices: towards hybrid CMOS-SET integrated circuits

Abstract: In this paper, CMOS evolution and their fundamental and practical limitations are briefly reviewed, and the working principles, performance, and fabrication of single-electron transistors (SETs) are addressed in detail. Some of the unique characteristics and functionality of SETs, like unrivalled integration and low power, which are complementary to the sub-20 nm CMOS, are demonstrated. Characteristics of two novel SET architectures, namely, C-SET and R-SET, aimed at logic applications are compared. Finally, it is shown that combination of CMOS and SET in hybrid ICs appears to be attractive in terms of new functionality and performance, together with better integrability for ULSI, especially because of their complementary characteristics. It is envisioned that efforts in terms of compatible fabrication processes, packaging, modeling, electrical characterization, co-design and co-simulation will be needed in the near future to achieve substantial advances in both memory and logic circuit applications based on CMOS-SET hybrid circuits.

Issues of nanoelectronics: a possible roadmap.

Abstract: In this review, we will discuss a possible roadmap in scaling a nanoelectronic device from today's CMOS technology to the ultimate limit when the device fails. In other words, at the limit, CMOS will have a severe short channel effect, significant power dissipation in its quiescent (standby) state, and problems related to other essential characteristics. Efforts to use structures such as the double gate, vertical surround gate, and SOI to improve the gate control have continually been made. Other types of structures using SiGe source/drain, asymmetric Schottky source/drain, and the like will be investigated as viable structures to achieve ultimate CMOS. In reaching its scaling limit, tunneling will be an issue for CMOS. The tunneling current through the gate oxide and between the source and drain will limit the device operation. When tunneling becomes significant, circuits may incorporate tunneling devices with CMOS to further increase the functionality per device count. We will discuss both the top-down and bottom-up approaches in attaining the nanometer scale and eventually the atomic scale. Self-assembly is used as a bottom-up approach. The state of the art is reviewed, and the challenges of the multiple-step processing in using the self-assembly approach are outlined. Another facet of the scaling trend is to decrease the number of electrons in devices, ultimately leading to single electrons. If the size of a single-electron device is scaled in such a way that the Coulomb self-energy is higher than the thermal energy (at room temperature), a single-electron device will be able to operate at room temperature. In principle, the speed of the device will be fast as long as the capacitance of the load is also scaled accordingly. The single-electron device will have a small drive current, and thus the load capacitance, including those of interconnects and fanouts, must be small to achieve a reasonable speed. However, because the increase in the density (and/or functionality) of integrated circuits is the principal driver, the wiring or interconnects will increase and become the bottleneck for the design of future high-density and high-functionality circuits, particularly for single-electron devices. Furthermore, the massive interconnects needed in the architecture used today will result in an increase in load capacitance. Thus for single-electron device circuits, it is critical to have minimal interconnect loads. And new types of architectures with minimal numbers of global interconnects will be needed. Cellular automata, which need only nearest-neighbor interconnects, are discussed as a plausible example. Other architectures such as neural networks are also possible. Examples of signal processing using cellular automata are discussed. Quantum computing and information processing are based on quantum mechanical descriptions of individual particles correlated among each other. A quantum bit or qubit is described as a linear superposition of the wave functions of a two-state system, for example, the spin of a particle. With the interaction of two qubits, they are connected in a "wireless fashion" using wave functions via quantum mechanical interaction, referred to as entanglement. The interconnection by the nonlocality of wave functions affords a massive parallel nature for computing or so-called quantum parallelism. We will describe the potential and solid-state implementations of quantum computing and information, using electron spin and/or nuclear spin in Si and Ge. Group IV elements have a long coherent time and other advantages. The example of using SiGe for g factor engineering will be described.

Fe-Filled Carbon Nanotubes: Nano-electromagnetic Inductors

Abstract: Fe-filled carbon nanotubes exhibit an electromagnetic induction in ac excitation mode, which suggest the possible construction of electrical nanomotors.

Molecular clusters as building blocks for nanoelectronics: the first demonstration of a cluster single-electron tunnelling transistor at room temperature

Abstract: This work is the result of coherent effort of a multi-disciplinary research team working for a considerable number of years in the former USSR in the area of nanocluster molecular electronics. For the first time the successful demonstration of a single-electron tunnelling transistor working reliably at room temperature and based on a single molecular metallorganic cluster is presented. A broad spectrum of different molecular clusters was investigated. Our group has developed a complete cycle of custom-designed molecular cluster manufacturing, deposition, characterization and modification of nanoelectronic devices based on a single molecular cluster. It was shown that the atomic and electronic structure of nanoclusters containing from 3 up to 23 metal atoms had no crucial importance for the transistor fabrication. At the same time extensive research into characteristics of nanoelectronic devices based on single molecular clusters and their tunnelling properties is summarized.

Template synthesis of Y-junction metal nanowires

Abstract: Template synthesis of large-scale Y-junction metal nanowires is reported. In this approach, a Y-shaped nanochannel porous anodic alumina (PAA) template is prepared by using a two-step anodization of aluminum in which the metal of interest, such as copper, is electrodeposited to form the Y-junction metal nanowires. The synthesis method presented here is simple and versatile. This method can be extended to the preparation of other Y-junction nanowires with desirable composition and shows great promise for the development of nanoelectronics.

Electron ratchet effect in semiconductor devices and artificial materials with broken centrosymmetry

Abstract: Studies on nonlinear electron transport in nanometer-sized semiconductor devices with broken centrosymmetry are reviewed. In these devices, an applied alternating (rocking) electric field induces a net flow of electrons in the direction perpendicular to that of the applied field. Such an electron ratchet effect has been observed in a number of differently designed devices, fabricated from two types of semiconductor material systems. The functionality is interpreted with an extended Buttiker-Landauer formula. We show that the devices operate at both cryogenic and room temperatures and at frequencies up to at least 50 GHz. Based on a similar microscopic mechanism, we have also constructed, to the best of our knowledge, the first artificial electronic nanomaterial that operates at room temperature. The promising possibilities for practical applications, such as rectification, microwave detection, second-harmonic generation, etc., are also discussed.

Organometallic precursor route to carbon nanotubes

Abstract: Multi-walled as well as single-walled carbon nanotubes are conveniently prepared by the pyrolysis of organometallic precursors, such as metallocenes and phthalocyanines, in a reducing atmosphere. Pyrolysis of organometallics alone or in mixture with hydrocarbons also yields aligned nanotube bundles with useful field emission properties. By pyrolyzing organometallics in the presence of thiophene, Y-junction nanotubes are obtained in large quantities. The junction nanotubes have a good potential in nanoelectronics. Carbon nano- tubes prepared from organometallics are useful for preparing nanowires and nanotubes of materials such as BN, GaN, SiC, and Si 3 N 4 .