Single-electron Tunneling Devices Research Articles

Nitrogen in silicon for room temperature single-electron tunneling devices

Single-electron transistor (SET) has an advanced feature that can be exploited in quantum devices. For practical utilization of such devices, the room-temperature operation is highly essential. Dopant-based single-electron devices are well studied at low temperatures although a few devices are developed for high-temperature operation with certain limitations. Here, we propose and theoretically exhibit that nitrogen (N) donor in silicon is an important candidate for the effective designing of quantum devices. Theoretical calculation of the density of states using the semi-empirical density functional theory method indicates that N-donor in silicon has a deep ground state compared to a phosphorus (P) donor. The N-donor spectrum is explored in nano-silicon structure along with the P-donor. A comparative study of the Bohr radius of N-donor and P-donor is also reported. The simulated current–voltage characteristics confirm that the N-doped device is better suited for SET operation at room temperature.

Reduced Electron Temperature in Silicon Multi-Quantum-Dot Single-Electron Tunneling Devices.

The high-performance room-temperature-operating Si single-electron transistors (SETs) were devised in the form of the multiple quantum-dot (MQD) multiple tunnel junction (MTJ) system. The key device architecture of the Si MQD MTJ system was self-formed along the volumetrically undulated [110] Si nanowire that was fabricated by isotropic wet etching and subsequent oxidation of the e-beam-lithographically patterned [110] Si nanowire. The strong subband modulation in the volumetrically undulated [110] Si nanowire could create both the large quantum level spacings and the high tunnel barriers in the Si MQD MTJ system. Such a device scheme can not only decrease the cotunneling effect, but also reduce the effective electron temperature. These eventually led to the energetic stability for both the Coulomb blockade and the negative differential conductance characteristics at room temperature. The results suggest that the present device scheme (i.e., [110] Si MQD MTJ) holds great promise for the room-temperature demonstration of the high-performance Si SETs.

An 8-Bit Full-Adder Implementation Using Single Electron Tunneling (SET) Technology (Dept.E)

Single Electron Tunneling (SET) devices have come to be considered as promising candidates for future ultra-low power and high-density integrated circuits. Their potential for ultra-low power is related to that the operation is based on only a few electrons. The term Single Electron Tunneling (SET) technology has been selected for devices sensitive to the manipulation of a single electron even if the device itself requires in fact few electrons. Besides, SET provides a simple and elegant solution for implementing threshold Logic Gates (TLGs). This paper presents a SET TLG one-bit full-adder implemented in SET technology. The paper then introduces the design and implementation of an 8-bit SET TLG full-adder and presents its SIMON 2 simulation results.

A Solution of the Two-Capacitor Problem Through its Similarity to Single-Electron Electronics

The purpose of this paper is to investigate the two-capacitor paradox using circuit models developed in the analysis of circuits that include nanoelectronic single-electron tunneling devices. The two-capacitor paradox, in which it seems that energy is not conserved in a simple circuit consisting of two capacitors in parallel separated by an ideal switch, is resolved by applying linear circuit theory utilizing a current—described by a (Dirac) delta function—and stepping voltages across all three elements. Based on a similar description, successfully used for tunneling of electrons through metal junctions in nanoelectronics, the switch is modeled as a device across which—upon closing—the voltage steps down while the current through it is an impulse. The model distinguishes three intervals in describing the ideal switch: t 0. As a consequence, the ideal switch dissipates energy during the switching action at t = 0 in zero time. Although the solution of the two-capacitor problem looks like a theoretical curiosity, the application of nanoelectronic concepts allow a physical explanation based on electron tunneling; it shows that the ideal switch is best described by the tunneling of many electrons. In such a context, some of those electrons loose energy and the v-i characteristic shows Ohm’s law.

Fundamental energy limits of SET-based Brownian NAND and half-adder circuits

The saturation in the efficiency and performance scaling of conventional electronic technologies brings about the development of novel computational paradigms. Brownian circuits are among the promising alternatives that can exploit fluctuations to increase the efficiency of information processing in nanocomputing. A Brownian cellular automaton, where signals propagate randomly and are driven by local transition rules, can be made computationally universal by embedding arbitrary asynchronous circuits on it. One of the potential realizations of such circuits is via single electron tunneling (SET) devices since SET technology enable simulation of noise and fluctuations in a fashion similar to Brownian search. In this paper, we perform a physical-information-theoretic analysis on the efficiency limitations in a Brownian NAND and half-adder circuits implemented using SET technology. The method we employed here establishes a solid ground that enables studying computational and physical features of this emerging technology on an equal footing, and yield fundamental lower bounds that provide valuable insights into how far its efficiency can be improved in principle. In order to provide a basis for comparison, we also analyze a NAND gate and half-adder circuit implemented in complementary metal oxide semiconductor technology to show how the fundamental bound of the Brownian circuit compares against a conventional paradigm.

Practical Quantum Realization of the Ampere from the Elementary Charge

One major change of the future revision of the International System of Units (SI) is a new definition of the ampere based on the elementary charge \emph{e}. Replacing the former definition based on Amp\`ere's force law will allow one to fully benefit from quantum physics to realize the ampere. However, a quantum realization of the ampere from \emph{e}, accurate to within $10^{-8}$ in relative value and fulfilling traceability needs, is still missing despite many efforts have been spent for the development of single-electron tunneling devices. Starting again with Ohm's law, applied here in a quantum circuit combining the quantum Hall resistance and Josephson voltage standards with a superconducting cryogenic amplifier, we report on a practical and universal programmable quantum current generator. We demonstrate that currents generated in the milliampere range are quantized in terms of $ef_\mathrm{J}$ ($f_\mathrm{J}$ is the Josephson frequency) with a measurement uncertainty of $10^{-8}$. This new quantum current source, able to deliver such accurate currents down to the microampere range, can greatly improve the current measurement traceability, as demonstrated with the calibrations of digital ammeters. Beyond, it opens the way to further developments in metrology and in fundamental physics, such as a quantum multimeter or new accurate comparisons to single electron pumps.

Room temperature Coulomb blockade mediated field emission via self-assembled gold nanoparticles

Coulomb blockade mediated field-emission current was observed in single-electron tunneling devices based on self-assembled gold nanoparticles at 300 K. According to Raichev's theoretical model, by fixing a proper geometric distribution of source, island and drain, the transfer characteristics can be well explained through a combination of Coulomb blockade and field emission. Coulomb blockade and field emission alternately happen in our self-assembled devices. The Coulomb island size derived from the experimental data is in good agreement with the average size of the gold nanoparticles used in the device. The integrated tunneling can be adjusted via a gate electrode.

Exciton complexes assisted transition channels in the optically excited single-electron tunneling units

The emission spectrum from the optically excited single electron tunneling devices, electrostatically coupled to a p-type side quantum dot, has been investigated. The 12 exciton-complexes transition processes have been found and can be classified into six electron-like and six hole-like transition processes. The self-consistent numerical analysis shows that the gate and bias voltages can be tuned to change the weight functions associated with the particular exciton-complexes transition processes, thereby influencing the intensity and frequency-dependence of the spontaneous emission signals. The energy discrepancies up to the quadratic terms with respect to bias voltages are taken into account to interpret different degrees of the Stark shifts experienced by the electron and the hole. There exist several competition mechanisms, where the increase of the gate voltage can neutralize the shift to lower-energy transition channels produced by the increase of the hole occupancy in the side dot, and the interdot repulsive and attractive Coulombic blockades compete with each other to determine the superiority or inferiority of the different resonance channels. The electron-like resonance channels can be switched to the hole-like ones or vice versa in the optical spectra by tuning the gate voltages.

Coulomb blockade of spin-dependent shuttling

We show that nanomechanical shuttling of single electrons may enable qualitatively new functionality if spin-polarized electrons are injected into a nanoelectromechanical single-electron tunneling (NEM-SET) device. This is due to the combined effects of spin-dependent electron tunneling and Coulomb blockade of tunneling, which are phenomena that occur in certain magnetic NEM-SET devices. Two effects are predicted to occur in such structures. The first is a reentrant shuttle instability, by which we mean the sequential appearance, disappearance and again the appearance of a shuttle instability as the driving voltage is increased (or the mechanical dissipation is diminished). The second effect is an enhanced spin polarization of the nanomechanically assisted current flow.

Single-electron shift-register circuit

This work presents a 4-bit shift-register designed with single-electron tunneling devices. Firstly, a single-electron D flip-flop based on NAND gates was designed and simulated. Based on D flip-flops, the shift-register architecture was also designed and successfully simulated at room temperature. Some considerations about noise margin were made. Moreover, stability analyses for the SET NAND, SET D flip-flop and SET shift-register were carried out.

Room-temperature characterization of gold self-assembled single electron tunneling devices

Graphical abstractDisplay Omitted Highlights? A single-electron-tunneling device was produced using pre-made gold nanoparticle. ? The nanodevice was fabricated by lithography with self-assembly technique. ? The nanodevice demonstrates Coulomb staircases at room temperature. Single-electron tunneling devices based on self-assembled gold nanoparticles have been fabricated. Two main transport mechanisms were found to interpret the conductive behaviors of the devices. One is attributed to the electron emission, and the other is depended on the bias tunneling with asymmetrical tunnel barriers. The resemblant Coulomb Blockade response was measured at room temperature. The charging energy is estimated to be much larger than the thermal energy. The Coulomb Island sizes calculated from the experimental data are consistent with the size range of the gold nanoparticles used in the self-assembly fabrication.

Sorter-Based Arithmetic Circuits for Sigma-Delta Domain Signal Processing—Part II: Multiplication and Algebraic Functions

We construct arithmetic modules for signal processing with sigma-delta modulated signal form which has advantage in signal quality over other pulsed signal forms. In the second part of this paper, multi-input multipliers are presented first. Secondly, dividers and square root function modules with the multiplier on their internal feedback path are constructed. Combined use of the multipliers, dividers, and the square root functions creates various algebraic functions including polynomial and rational functions. Only two bit-manipulations, bit-permutation with sorting networks and bit-reversal with NOT gates, have built up all the algebraic operations on any form of SD modulated signals. These modules, together with transcendental functions presented in the first part of this paper, organize an extensive module library for the sigma-delta domain signal processing. The multiplier output contains noise components which originate from quantization. The noise power can decrease in exchange for circuit complexity. A time-division multiplexing technique based on N-tone sigma-delta modulation is applied to the multipliers for reducing the complexity. Signal processing circuits built of nanometer-scale quantum effect devices must be equipped with fault tolerance of transient device error. By computer simulation of a multiplier built of single-electron tunneling devices, we found that the multiplier decreased its output SNDR from 43 to 27 dB at an OSR of 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</sup> as the device error rate increased from 0 to 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> . However, the multiplier was never functionally failed during the simulation.

Electron temperature in electrically isolated Si double quantum dots

Charge-based quantum computation can be attained through reliable control of single electrons in lead-less quantum systems. Single-charge transitions in electrically isolated double quantum dots (DQDs) realised in phosphorus-doped silicon can be detected via capacitively coupled single-electron tunnelling devices. By means of time-resolved measurements of the detector’s conductance, we investigate the dots’ occupancy statistics in temperature. We observe a significant reduction of the effective electron temperature in the DQD as compared to the temperature in the detector’s leads. This sets promises to make isolated DQDs suitable platforms for long-coherence quantum computation.

Electron Counting Capacitance Standard with an improved five-junction R-pump**Official contribution of the National Institute of Standards and Technology; not subject to copyright in the United States.

The Electron Counting Capacitance Standard currently pursued at PTB aims to close the Quantum Metrological Triangle with a final precision of a few parts in 107. This paper reports the considerable progress recently achieved with a new generation of single-electron tunnelling devices. A five-junction R-pump was operated with a relative charge transfer error of five electrons in 107, and was used to successfully perform single-electron charging of a cryogenic capacitor. The preliminary result for the single-electron charge quantum has an uncertainty of less than two parts in 106 and is consistent with the value of the elementary charge.

Single-charge escape processes through a hybrid turnstile in a dissipative environment

We have investigated the static, charge-trapping properties of a hybrid superconductor–normal metal electron turnstile embedded in a high-ohmic environment. The device includes a local Cr resistor on one side of the turnstile, and a superconducting trapping island on the other side. The electron hold times, τ∼2–20 s, in our two-junction circuit are comparable with those of typical multi-junction, N⩾4, normal-metal single-electron tunneling devices. A semi-phenomenological model of the environmental activation of tunneling is applied for the analysis of the switching statistics. The experimental results are promising for electrical metrology applications.

Determination of the elementary charge and the quantum metrological triangle experiment

The elementary charge e is of fundamental importance in physics. The determination of its value, which is closely linked to progress of the measurement techniques, started in the beginning of the twentieth century and is still on-going. Today, in the frame of the CODATA adjustment, the evaluation of the fundamental constant, e, is derived from a complex calculation and is no more related to a single experiment. But the development of single electron tunneling (SET) devices, started in the early 90s, has opened the path towards modern metrological systems as quantum current sources. Thus a new direct determination of e is possible by implementing an electron pump and the set-up of the quantum metrological triangle (QMT) in combination with the experiments linking mechanical and electrical units. Furthermore, we show how the QMT experiment can contribute to the establishment of a new system of units based on fundamental constants of physics.

Why the long-term charge offset drift in Si single-electron tunneling transistors is much smaller (better) than in metal-based ones: Two-level fluctuator stability

A common observation in metal-based (specifically, those with AlOx tunnel junctions) single-electron tunneling (SET) devices is a time-dependent instability known as the long-term charge offset drift. This drift is not seen in Si-based devices. Our aim is to understand the difference between these, and ultimately to overcome the drift in the metal-based devices. A comprehensive set of measurements shows that (1) brief measurements over short periods of time can mask the underlying drift, (2) we have not found any reproducible technique to eliminate the drift, and (3) two-level fluctuators (TLFs) in the metal-based devices are not stable. In contrast, in the Si-based devices the charge offset drifts by less than 0.01e over many days, and the TLFs are stable. We also show charge noise measurements in a SET device over four decades of temperature. We present a model for the charge offset drift based on the observation of nonequilibrium heat evolution in glassy materials, and obtain a numerical estimate in good agreement with our charge offset drift observations. We conclude that, while the Si devices are not perfect and defect-free, the defects are stable and noninteracting; in contrast, the interacting, unstable glasslike defects in the metal-based devices are what lead to the charge offset drift. We end by suggesting some particular directions for the improvement in fabrication, and in particular, fabrication with crystalline metal-oxide barriers, that may lead to charge offset drift-free behavior.

Interconnection effects on the performance of basic subcircuits with single-electron tunneling devices

Interconnection limits seem to be a potential problem to the evolution of the semiconductor industry, especially in the nanoscale. In this work, the electrical performance of basic cells is studied with the help of a simple interconnection model, whose parameters can be changed. Our goal, with this study, is to determine the interconnection's influence upon the circuit behavior and to establish interconnection-related limits for its functionality. An extrapolation to more complex circuit topologies is also discussed. Finally, the implementation possibilities using new interconnection technologies, like carbon nanotubes, are presented.

Metrology triangle using a Watt balance, a calculable capacitor and a single-electron tunnelling device

The combination of a Watt balance, a calculable capacitor and a single-electron tunnelling device forms a triangle that yields a value for the single-electron charge quantum QS in terms of the SI coulomb. Importantly, this result is independent of the Josephson and quantum Hall effects, and thus avoids the possible confounding corrections from these two effects that arise in the traditional quantum metrology triangle. This new triangle can be used to test for corrections to the expected relation QS = e, where e is the elementary charge. Combining existing results for Watt balances, calculable capacitors and an electron counting capacitance standard yields (QS/e) − 1 = (−0.09 ± 0.92) × 10−6.

Self-Organization of Irregular Nanoelectromechanical Vibrations in Multimode Shuttle Structures

We investigate theoretically multimode electromechanical "shuttle" instabilities in dc voltage-biased nanoelectromechanical single-electron tunneling devices. We show that initially irregular (quasiperiodic) oscillations that occur as a result of the simultaneous self-excitation of several mechanical modes with incommensurable frequencies self-organize into periodic oscillations with a frequency corresponding to the eigenfrequency of one of the unstable modes. This effect demonstrates that a local probe can selectively excite global vibrations of extended objects.