Single-Flux-Quantum Bipolar Digital-to-Analog Converter Comprising Polarity-Switchable Double-Flux-Quantum Amplifier

We present a single-flux-quantum (SFQ)-based digital-to-analog converter (DAC) generating bipolar output voltages, in which the key component is a polarity-switchable double-flux-quantum amplifier (PS-DFQA). The DAC comprised a dc/SFQ converter, an 8-bit variable pulse-number-multiplier (PNM), and a 8-fold PS-DFQA integrated on a single chip. SFQ pulse-frequency modulation was employed to realize variable output voltage amplitude, for which the multiplication factor of the variable-PNM was controlled by a commercial data generator situated at room temperature. The variable-PNM realized 8-bit resolution with a multiplication factor between 0 and 255. Bias currents fed to the 8-fold PS-DFQA were polarity-switched in synchronization with the digital code for the variable-PNM. The whole circuits including I/O elements were designed using SFQ cell libraries, and fabricated using a niobium integration process. Sinusoidal bipolar voltage waveform of 0.38 mVpp was demonstrated using a reference signal source of 43.94 MHz

Numerical Simulation of Single-Electron Tunneling in Random Arrays of Small Tunnel Junctions Formed by Percolation of Conductive Nanoparticles

We numerically simulated electrical properties, i.e., the resistance and Coulomb blockade threshold, of randomly-placed conductive nanoparticles. In simulation, tunnel junctions were assumed to be formed between neighboring particle-particle and particle-electrode connections. On a plane of triangle 100×100 grids, three electrodes, the drain, source, and gate, were defined. After random placements of conductive particles, the connection between the drain and source electrodes were evaluated with keeping the gate electrode disconnected. The resistance was obtained by use of a SPICE-like simulator, whereas the Coulomb blockade threshold was determined from the current-voltage characteristics simulated using a Monte-Carlo simulator. Strong linear correlation between the resistance and threshold voltage was confirmed, which agreed with results for uniform one-dimensional arrays

Fabrication of resistively-coupled single-electron device using an array of gold nanoparticles

We demonstrated one type of single-electron device that exhibited electrical characteristics similar to those of resistively-coupled SE transistor (R-SET) at 77 K and room temperature (287 K). Three Au electrodes on an oxidized Si chip served as drain, source, and gate electrodes were formed using electron-beam lithography and evaporation techniques. A narrow (70-nm-wide) gate electrode was patterned using thermal evaporation, whereas wide (800-nm-wide) drain and source electrodes were made using shadow evaporation. Subsequently, aqueous solution of citric acid and 15-nm-diameter gold nanoparticles (Au NPs) and toluene solution of 3-nm-diameter Au NPs chemisorbed via decanethiol were dropped on the chip to make the connections between the electrodes. Current–voltage characteristics between the drain and source electrodes exhibited Coulomb blockade (CB) at both 77 and 287 K. Dependence of the CB region on the gate voltage was similar to that of an R-SET. Simulation results of the model based on the scanning electron microscopy image of the device could reproduce the characteristics like the R-SET

Gate-tuned negative differential resistance observed at room temperature in an array of gold nanoparticles

We fabricated a single-electron (SE) device using gold nanoparticles (Au NPs). Drain, source, and gate electrodes on a SiO2/Si substrate were formed using electron beam lithography (EBL) and thermal evaporation of Au. Subsequently, solutions of 3-nm-diameter and 5-nm-diameter Au NPs were dropped on the device to make current paths through Au NPs among the electrodes. Measurements of the device exhibited negative differential resistance (NDR) in the current-voltage characteristics between the drain and source electrodes at room temperature (298 K). The NDR behavior was tuned by applying a gate voltage

1000-Fold Double-Flux-Quantum Voltage Multiplier Employing Directional Propagation of Flux Quanta Through Asymmetrically Damped Junction Branches

Precise voltage generation is a unique feature of single-flux-quantum (SFQ) circuits, in addition to their high-speed digital signal processing with low power consumption. We investigated SFQ pulse-frequency modulation D/A converters for metrological applications. In our SFQ-based D/A converters, the maximum output voltage is determined by the maximum SFQ pulse-frequency at the pulse number multiplier, and by the voltage multiplication factor at the voltage multiplier. In this study, we present our new design for a double-flux-quantum amplifier (DFQA) that works as a quantum voltage multiplier. In the new parameter set, we tuned the damping parameters of the Josephson junctions to realize proper propagation of SFQ pulses. A 1000-fold DFQA designed with the new parameter set was fabricated using a 25-μ A/μ m 2 Nb/AlOx/Nb integration technology. A 1000-fold voltage multiplication was confirmed for the input voltage up to 43 μV, with a corresponding SFQ repetition frequency of 21 GHz. That is, the output voltage reached 43 mV

4-bit Bipolar Triangle Voltage Waveform Generator Using Single-Flux-Quantum Circuit

AbstractSFQ digital-to-analog converters (DACs) are one of the candidates for AC voltage standards. We have proposed SFQ-DACs based on frequency modulation (FM). Bipolar output is required for applications of AC voltage standards, while our previous SFQ-DACs generated only positive voltages. In this paper, we present our design of a 4-bit bipolar triangle voltage waveform generator comprising an SFQ-DAC. The waveform generator has two output ports. Synthesized half-period waveforms are alternately generated in one of the output ports. The bipolar output is realized by observing the differential voltage between the ports. We confirmed a 72-μVPP bipolar triangle voltage waveform at the frequency of 35.7Hz