Takahide Oya

A majority-logic device using an irreversible single-electron box

We describe a majority-logic gate device suitable for use in developing single-electron integrated circuits. The device consists of a capacitor array for input summation and an irreversible single-electron box for threshold operation. It accepts three binary inputs and produces a corresponding output, a complementary majority-logic output, by using the change in its tunneling threshold caused by the input signals; it produces a logical 1 output if two or three of the inputs are logical 0 and a logical 0 output if two or three of the inputs are logical 1. We combined several of these gate devices to form subsystems, a shift register and a full adder, and confirmed their operation by computer simulation. The gate device is simple in structure and powerful in terms of implementing digital functions with a small number of devices. These superior features will enable the device to contribute to the development of single-electron integrated circuits.

SINGLE-ELECTRON CIRCUITS PERFORMING DENDRITIC PATTERN FORMATION WITH NATURE-INSPIRED CELLULAR AUTOMATA

We propose a novel semiconductor device in which electronic-analogue dendritic trees grow on multilayer single-electron circuits. A simple cellular-automaton circuit was designed for generating dendritic patterns by utilizing the physical properties of single-electron devices, i.e. quantum and thermal effects in tunneling junctions. We demonstrate typical operations of the proposed circuit through extensive numerical simulations.

Thermal-Noise-Exploiting Operations of Single-Electron Majority Logic Circuits with Conventional Clock Signals

This paper describes a thermal-noise-exploiting single-electron majority logic circuit. The circuit is based on a single-electron majority logic circuit using an irreversible single- electron box that was proposed in 2003. To correctly operate the original circuit, unconventional two-step clock signals are needed to decide and hold logical outputs. Moreover, the temperature is set to 0 K because the circuit is very sensitive to thermal noise. This circuit uses conventional clock signals that lack the first step of the two-step clocks used for deciding the output, and the circuit is placed in a thermal-noise environment. The key for correct circuit operation is to base the circuit system on a model of noise- exploiting neural networks, i.e., the stochastic resonance system. The system can stochastically detect a weak input signal with the help of external noise. Thermal energy in the proposed circuit should compensate for lack of the first step of the two-step clocks. In this study, the thermal-noise-exploiting majority logic circuit was designed, and its operation was tested by using a Monte Carlo simulation. As a result, the circuit operation was evaluated, and the circuit performance was found to be improved by increasing the temperature to T ≤ 5 K, i.e., the proposed circuit can exploit thermal noise energy for correct operation.

Multifunctional Device Using Nanodot Array

We have fabricated a new single-electron device (SED) that has many nanodots. Although SEDs have the great advantages of small size and low power consumption, they should have small dots on the order of a few nanometers, which makes them difficult to fabricate. The proposed device uses many nanodots aligned as an array, on which many gate electrodes are attached so as to couple capacitively to underlying nanodots. Some of the gates are used as input gates of a logic-gate device. The others are control gates that are used to change the logic function of the device, such as from an AND gate to an XOR (exclusive OR) one. The principal operations have been demonstrated using numerical simulations.

Control of Chemical States on Locally Anode-Oxidized Si Surfaces

We have demonstrated that chemical states on the anode-oxidized Si surfaces prepared by atomic force microscopy (AFM) can be controlled by selecting the appropriate applied voltage for the oxidation. The frictional force on the oxidized surface formed at relatively low voltages (4.5–9 V) was large, whereas that at relatively high voltages (9–10 V) was small. This is due to a difference in the hydrophilicity of the surfaces. Octadecyltrichlorosilane (OTS) films were formed only on the oxidized surface prepared at the low voltages. Since OTS molecules require OH groups to form a film, the hydrophilicity originates from OH group termination of the surfaces. Therefore, the oxide surface is terminated with OH groups when the applied voltage is relatively low. When the applied voltage is relatively high, it is speculated that the oxide surface is covered with Si–O–Si groups instead of OH groups.

On the Fault-Tolerance of a Clustered Single-Electron Neural Network for Differential Enhancement

Reference LSM-ARTICLE-2005-003View record in Web of Science Record created on 2005-11-21, modified on 2017-05-10

Fabrication of Aligned-Carbon-Nanotube-Composite Paper with High and Anisotropic Conductivity

A functional carbon-nanotube (CNT)-composite paper is described in which the CNTs are aligned. This “aligned-CNT composite paper” is a flexible composite material that has CNT functionality (e.g., electrical conductivity) despite being a paper. An advanced fabrication method was developed to overcome the problem of previous CNT-composite papers, that is, reduced conductivity due to random CNT alignment. Aligning the CNTs by using an alternating current (AC) field was hypothesized to increase the electrical conductivity and give the paper an anisotropic characteristic. Experimental results showed that a nonionic surfactant was not suitable as a CNT dispersant for fabricating aligned-CNT composite paper and that catechin with its six-membered rings and hydrophilic groups was suitable. Observation by scanning electron microscopy of samples prepared using catechin showed that the CNTs were aligned in the direction of the AC field on the paper fibers. Measurement of the electric conductivity showed that the surface resistance was different between the direction of the aligned CNTs (high conductivity) and that of verticality (low). The conductivity of the aligned-CNT-composite paper samples was higher than that of nonaligned samples. This unique and functional paper, which has high and anisotropic conductivity, is applicable to a conductive material to control the direction of current.

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. [Article copies are available for purchase from InfoSci-on-Demand.com]

Study of two-dimensional device-error-redundant single-electron oscillator system

This paper reports the study of a two-dimensional device-error-redundant single-electron (SE) circuit. The circuit is an SE reaction-diffusion (RD) circuit that imitates the unique behavior of the chemical RD system and is expected to be a new information processing system. The original RD system is a complex chemical system that is said to express selforganizing dynamics in nature. It can also be assumed to operate as parallel information processing systems. Therefore, by imitating the original RD system for SE circuits, this SE-RD circuit can perform parallel information processing that is based on a natural phenomenon. However, the circuit is very sensitive to noise because it is controlled by a very small amount of energy. It is also sensitive to device errors (e.g., circuit parameter fluctuations in the fabrication process). Generally, fluctuations caused by errors introduced in manufacturing the circuit components trigger incorrect circuit operations, including noises. To overcome such noises, the circuit requires redundant properties for noise. To address this issue, we consider mimicking the information processing method of the natural world for the circuit to obtain noise redundancy. Actually, we previously proposed a unique method based on a model of neural networks with a stochastic resonance (SR) for the circuit. The SR phenomenon, which was discovered in studies of living things (e.g., insects), can be considered a type of noise-energy-harnessing system. Many researchers have proposed SR-based applications for novel electronic devices or systems. In networks where SR exists, signals can generally be distinguished from noise by harnessing noise energy. We previously designed SE-SR systems and succeeded in making an architecture for an SE circuit that has thermal noise redundancy. At the time, we applied an SR model proposed by Collins to our circuit. Prior to our current study, however, it had not yet been confirmed whether SE circuits have device-error redundancy. In this study, we attempt to confirm this by using Monte Carlo simulation to study the characteristics of the abovementioned SE-RD circuit. Simulation results indicate that the SE-RD circuit, which is based on an SR model, has not only deviceerror redundancy but also thermal noise redundancy. The circuit is therefore expected to prove that the parameter matching step in the circuit fabrication process can be omitted.

Study of stochastic resonance in a quantum dot network

This paper reports a study of stochastic resonance in a huge quantum dot network for single-electron (SE) circuits. Such circuits, which are controlled by the Coulomb blockade, are one type of next-generation information-processing device. However, they are very sensitive to noises such as thermal noise and device mismatch noise. Thus, we introduce the stochastic resonance phenomenon into the circuit to improve its noise tolerance. Stochastic resonance is a phenomenon that was discovered in the brains of living things in noisy environments and was modeled for neural networks. When the phenomenon occurs, its harnessing of noise energy makes weak signals become clear. In current research, SE devices that operate with stochastic resonance have been reported. However, signals were attenuated in particularly noisy environments. In contrast, it was reported that a huge molecular network amplified weak signals by harnessing noise energy. The report said the current-voltage characteristics of the molecular network described the Coulomb blockade under a noisy environment. Thus, a huge quantum dot network that is partly similar to a molecular network is expected to amplify the weak signal harnessing noise, when the current-voltage characteristics of the network show the Coulomb blockade. To confirm this, in this study we use the Monte Carlo method to simulate the noisy-environment operation of a quantum dot network comprising quantum dots and tunneling junctions. We observe the current-voltage characteristics of the network, when changing the network size (5×5, 10×10, and 100×100) and the noise intensity (0 K, 2 K, 5 K, and 10 K for operating temperature, and 0%, 5%, 10%, and 30% for device mismatch). As a result, we are able to observe the Coulomb blockade under the appropriate noise strength, which in this study is 5 K or less with thermal noise, and 30% with device mismatch. From the results, we conclude the network operates correctly under appropriate noise strength. Moreover, the noise energy amplifies the network current, indicating that SE circuits can function as signal-amplifying devices.