Single-electron Devices Research Articles

Single-Electron Device With Si Nanodot Array and Multiple Input Gates

We have developed a flexible-logic-gate single-electron device (SED) with an array of nanodots. Although the small size of SEDs is highly advantageous, the size of the nanodots inevitably fluctuates, which causes variations in device characteristics. This variability can be eliminated and high device functionality can be obtained by exploiting the oscillatory characteristics and multigate capability of SEDs. We fabricated, on a silicon-on-insulator wafer, a Si nanodot array device with two input gates and a control gate and investigated its basic operation characteristics experimentally. The device was demonstrated to operate as a logic gate providing six important logic functions ( and, or, nand, nor, xor, and xnor), which are obtained by adjusting the control-gate voltage.

Diagrammatic real-time approach to adiabatic pumping through metallic single-electron devices

We present a real-time diagrammatic formalism to study adiabatic pumping in chains of tunnel-coupled metallic islands. This approach is based on an expansion to linear order in the frequency of the time-dependent parameters and on a systematic perturbation expansion in the tunnel-coupling strength. We apply our formalism to single-island and double-island systems. In the single-island setup, we find that the first-order contribution in the tunnel-coupling strength is purely due to the renormalization of the charging-energy gap. In the double-island system, we investigate the transition between weak and strong pumping.

Gate control of a quantum dot single-electron spin in realistic confining potentials: Anisotropy effects

Among recent proposals for next-generation, non-charge-based logic is the notion that a single electron can be trapped and its spin can be manipulated through the application of gate potentials. In this paper, we present numerical simulations of such spins in single electron devices for realistic (asymmetric) confining potentials in two-dimensional electrostatically confined quantum dots. Using analytical and numerical techniques we show that breaking the in-plane rotational symmetry of the confining potential leads to a significant effect on the tunability of the g-factor with applied gate potentials. In particular, anisotropy extends the range of tunability to larger quantum dots.

Ar + ion milling of InSb for manufacturing single electron devices

Ar + ion milling of InSb for manufacturing single electron devices was studied. It is shown that pyramidal structures (porous) are created on the (1 1 1) surface of InSb wafers by anisotropic etching. Also it was shown the axis of the pyramidal structure is a function of the angle of the Ar + incident beam and does not depend on the energy of the beam. EDX measurement results show In x O y and Sb x O y were not created on the surface after milling process. FTIR measurement results show that the surface reflection was decreased and less than 0.3 V flat band voltage was seen in capacitance voltage measurement results. SEM images show that the etching has approximately vertical profile. Therefore the Ar + milling technique can be used as a dry etching technique for manufacturing mesa and/or porous structures of InSb. Since the surface is porous and of near-pyramidal morphology, one can simulate the surface by a set of needles each of which is a nanometer-size capacitance (i.e. single electron device). We showed, the threshold voltage of this single electron device is 0.3 V approximately, and therefore it can be used for studying single-electron or Coulomb blockade effects.

Application of Single Electron Devices Utilizing Stochastic Dynamics

Single electron devices utilizing the Coulomb blockade phenomenon have attractive features such as extreme low power consumption, one by one electron flow controllability, small device size, etc. However, besides promising applications such as the current standard and charge detection, it is not easy to apply the single electron devices to conventional computational tasks due to its stochastic operation and low amplification capability. Therefore, it is important for us to consider suitable applications of single electron devices. In this paper, we show three applications such as a noise generator, a stochastic neural network, and a charge detector employing stochastic resonance. Trough these applications, we see the advantages of single electron devices and study the direction of applications.

A Neuromorphic Single-Electron Circuit for Noise-Shaping Pulse-Density Modulation

We propose a bio-inspired circuit performing pulse-density modulation with single-electron devices. The proposed circuit consists of three single-electron neuronal units, receiving the same input and are connected to a common output. The output is inhibitorily fedback to the three neuronal circuits through a capacitive coupling. The circuit performance was evaluated through Monte-Carlo based computer simulations. We demonstrated that the proposed circuit possesses noise-shaping characteristics, where signal and noises are separated into low and high frequency bands respectively. This significantly improved the signal-tonoise ratio (SNR) by 4.34 dB in the coupled network, as compared to the uncoupled one. The noise-shaping properties are as a result of i) the inhibitory feedback between the output and the neuronal circuits, and ii) static noises (originating from device fabrication mismatches) and dynamic noises (as a result of thermally induced random tunneling events) introduced into the network.

Single-Electron Devices and Circuits Utilizing Stochastic Operation for Intelligent Information Processing

The single-electron circuit technology should aim at developing information processing systems using the intrinsic properties of single-electron devices. The operation principles of single-electron devices are completely different from that of conventional CMOS devices, but both devices should co-exist in the information processing systems. In this paper, according to a scenario for achieving large-scale integrated systems of single-electron devices, some single-electron devices and circuits utilizing stochastic operation for associative processing and a spiking neuron model are described.

Electronic transport in silicon nanocrystals and nanochains

Si nanocrystals and nanochains, prepared by material synthesis, provide a means to define nanoscale devices using growth rather than lithographic techniques. Electronic transport in thin films of Si nanocrystals is influenced strongly by single-electron charging and quantum-confinement effects, and by the grain boundary regions between nanocrystals. This paper reviews electronic transport mechanisms in Si nanocrystal materials. These include thermionic emission of electrons across grain boundaries, space charge limited current, hopping transport, and single-electron charging effects. The fabrication of single-electron devices in Si nanocrystal thin films and nanochains is considered, particularly with regards to their operation at room temperature.

Single-Gated Single-Electron Transfer in Nonuniform Arrays of Quantum Dots

Single-electron transfer in single-gated one-dimensional quantum dot arrays is investigated statistically from the viewpoint of robustness against parameter fluctuations. We have found numerically that inhomogeneous quantum dot arrays formed in doped nanowires exhibit single-electron transfer over a wide range of parameters. This confirms our frequent experimental observation of single-electron transfer in doped-nanowire field-effect transistors. The most important result in this work is that three-dot arrays with small-large-small dot size distribution always allow single-electron transfer even if dot sizes fluctuate. This structure is, we believe, most promising for fabricating devices with high immunity against structural fluctuations on the nanometer scale. On the basis of these findings, we propose methods to fabricate high-yield single-electron transfer devices.

Conductance of the capacitively coupled single-electron transistor with a Tomonaga-Luttinger liquid island in the Coulomb blockade regime

We consider the electron transport in the capacitively coupled single-electron transistor with an ultrasmall Tomonaga-Luttinger liquid island. The charging effects, as well as the Tomonaga-Luttinger liquid nature, are treated by a self-consistent theory of the Coulomb blockade using the open boundary bosonization technique. Analytical expressions for conductance are derived in the limits of low and high voltages and temperatures, for bulk and edge island contact geometries, and for arbitrary environmental impedance. For an infinite system, we obtain the power law of the conductance with the exponent changed from the usual Tomonaga-Luttinger exponent due to the effects of the electromagnetic environment. For a finite system, we obtain expressions for the conductance as a function of voltage near the Coulomb blockade boundary and as a function of temperature for low temperatures; these expressions differ from the usual power-law behavior. The results show the potential for improving the accuracy of single-electron devices such as those used in electrical metrology.

Development of single-electron devices and molecular devices by highly precise bottom-up processes and scanning probe microscopy

Development of single-electron devices and molecular devices by highly precise bottom-up processes and scanning probe microscopy

An Elementary Neuro-Morphic Circuit for Visual Motion Detection with Single-Electron Devices Based on Correlation Neural Networks

An Elementary Neuro-Morphic Circuit for Visual Motion Detection with Single-Electron Devices Based on Correlation Neural Networks

Current-Induced Magnetic Dynamics in Asymmetric Ferromagnetic Single-Electron Devices

The theoretical calculations of possible dynamics for a localized magnetic moment of the central electrode in a ferromagnetic single-electron devices are presented. The spin-transfer torque from spin current absorbed by the central electrode is calculated. Thereafter, an in-plane component of spin torque is regarded during the integration of Landau-LifsitzGilbert equation and the time evolution of the localized magnetic moment of the central electrode is obtained. The necessary conditions for switching of the magnetic moment is discussed.

Electron beam induced deposited etch masks

In this paper we present a method based on electron beam induced deposition (EBID) to fabricate small electrodes with sub-10 nm gaps as required e.g. in single electron devices. EBID provides nanometer resolution combined with a relatively high throughput and reproducibility. Some known drawbacks of EBID are the limited choice of materials, inclusion of large amounts of carbon and low aspect ratio (AR) in the sub-10 nm regime. These drawbacks have been circumvented by using EBID deposits as an etch mask to pattern other materials, rather than using EBID to deposit the electrodes directly. Using this method 15–20 nm wide electrodes separated by a 7 nm gap were successfully fabricated.

Analytical Study on a Single Electron Device with Two Islands Connected to One Gate Electrode

We have studied a double-dot single electron device that includes three tunnel junctions connecting a source, two islands and a drain, and a gate electrode capacitively connected to the two islands. Analytical solutions for voltage distribution and Coulomb blockade conditions were derived for the double-dot device with a symmetrical equivalent circuit by solving equations algebraically. With the help of derived formulas, stability diagrams for the device were drawn and the device operation was investigated in detail. Large and small rhombic stability diagrams are arranged alternately along the Vg axis. Large rhombic diagrams change to hexagonal shape, depending on a ratio of capacitances. A single electron can transfer from the source to the drain through the islands, that is, the device operates as a single electron transistor. The stability diagrams suggested that periodic double peaks of the drain current would appear. We also proved that this device cannot operate as a single electron turnstile.

Virtual electron diffusion through a quantum dot in the presence of electromagnetic fluctuations

We consider a double junction system in the Coulomb blockade regime with an island with discrete energy levels and analyze the effect of electromagnetic fluctuations on elastic cotunneling. We obtain the analytic expression for the elastic cotunneling current at zero temperature, which shows the power-law suppression of cotunneling at low voltages due to circuit impedance $I\ensuremath{\sim}{V}^{1+2\text{ }\text{Re}\text{ }Z(0)/{R}_{K}}$. The results will be useful for calculating the accuracy of single-electron devices used in metrology.

Silicon nanodot-array device with multiple gates

We fabricated a nanodot-array device with multiple input gates on a silicon-on-insulator (SOI) wafer by using a pattern-dependent oxidation method with multiple input gates, which embodies a new concept of a flexible single-electron device. Although the device can generate many logic functions owing to the capacitive coupling between dots and many gates, the complicated structural configuration makes it difficult to confirm the formation of the nanodot array. For further investigation of this kind of device to achieve higher functionality, it is important to demonstrate experimentally that the dot array is actually formed. We analyzed the oscillation-peak shift caused by the gate voltage change, and successfully determined the location of the dots that contributed to the experimentally observed oscillations.

CMOS-compatible fabrication of room-temperature single-electron devices

Devices in which the transport and storage of single electrons are systematically controlled could lead to a new generation of nanoscale devices and sensors. The attractive features of these devices include operation at extremely low power, scalability to the sub-nanometre regime and extremely high charge sensitivity. However, the fabrication of single-electron devices requires nanoscale geometrical control, which has limited their fabrication to small numbers of devices at a time, significantly restricting their implementation in practical devices. Here we report the parallel fabrication of single-electron devices, which results in multiple, individually addressable, single-electron devices that operate at room temperature. This was made possible using CMOS fabrication technology and implementing self-alignment of the source and drain electrodes, which are vertically separated by thin dielectric films. We demonstrate clear Coulomb staircase/blockade and Coulomb oscillations at room temperature and also at low temperatures.

Single-Electron Devices With Input Discretizer

We propose an input discretizer for single-electron (SE) devices. The input discretizer is composed of one small tunnel junction and two capacitances. Adjusting the capacitances to be equal discretizes the gate charge with interval of a half of the elementary charge <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</i> , which enhances the performance of SE devices. An SE transistor with the input discretizer has abrupt switchings of the Coulomb blockade thresholds, resulting in steep responses to the input signal. An SE turnstile with the input discretizer enhances its operation margins for the application of a digital-to-analog converter element. Both analytical and numerical results are presented.

Anodic Oxidation Technique using an Atomic Force Microscope to Fabricate a Single-Electron Device for a Radiation Imaging Detector

We have employed an anodic oxidation technique using an atomic force microscope to fabricate a single-electron transistor (SET) as the nanoscale thermometer for the new real-time radiation imaging detector with nanometer spatial resolution proposed for isotope ratio mass spectroscopy. We have estimated the precision of the anodic oxidation technique in making an oxide on a thin Ti film deposited on a SiO2 substrate, and determined the conditions for forming the oxides. It is found that the size of the oxide can be controlled in the nanometer scale from 100 to 240 nm with the precision of 15 nm for the oxide width and a positional precision of 23 nm under the relative humidity of 60%.