Arrays Of Small Tunnel Junctions Research Articles

Coherence of oscillations generated by single-electronic two-dimensional arrays of tunnel junctions

The single-electron devices (SEDs) are novel devices based on a new operation concept and technologies, with great scaling potential that has been fabricated and is under investigation. The SEDs are based on the controllable transfer of single electrons (SEs) between small conducting electrodes. They have had already several demonstrative scientific experiments as well as enabled fabrication methods. The present work studies the coherence of signals in a two-dimensional homogeneous arrays of small tunnel junctions. The Monte-Carlo technique is used to simulate the circuit and collect the required statistics. The simulator is a hybrid simulator that uses at the beginning the Master Equation representation to compute the steady-state current through the circuit. It is shown, how the coherence of oscillations is strengthened with longer arrays structures, and that the coupled two-dimensional long arrays are having strong correlated tunnel events, when the finite frequency noise characteristics and oscillations pattern variation are addressed. The variation of both the applied voltage and the coupling capacitors is illustrated. The dependency of the transport process and distribution of time between the events on their setting parameters is shown and the coefficient of variation was calculated to clarify the results. Also, the state’s transition flow is reviewed for the traverse of electrons through the arrays structure for different bias conditions.

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

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

Monte Carlo study of charge transport in slantingly coupled arrays of small tunnel junctions

We present a numerical investigation on the charge transport in capacitively coupled arrays of small tunnel junctions in the case of slanted coupling. Current-voltage characteristics of the arrays having various coupling capacitance $({C}_{c})$ are simulated using the Monte Carlo method. In contrast to the case of straight coupled arrays, slantingly coupled arrays exhibit the current mirror effect using a coupling capacitance as small as ${C}_{c}∕C\ensuremath{\simeq}0.1$, where $C$ is the junction capacitance. However, when ${C}_{c}$ is too large $({C}_{c}∕C>1)$, electron-electron or hole-hole chains are formed in each array, which deteriorate the current mirror effect. Conditions for the formation of such chains are derived from analysis of a simplified model of slantingly coupled arrays.

Experimental test of the correction terms for Coulomb blockade thermometry

We have experimentally investigated the higher-order correction terms for Coulomb blockade thermometry using two-dimensional arrays of small tunnel junctions and compared our results to the theory for one-dimensional arrays. We find that the correction term for the conductance dip is two times smaller, whereas the correction term for the half-width has a slightly higher value than the theoretical prediction.

Numerical investigation on the current mirror effect in a single-electron turnstile capacitively coupled to a one-dimensional array of small junctions

We present numerical results of an examination of the current mirror effect in a single-electron turnstile capacitively coupled to a one-dimensional (1D) array of small tunnel junctions. We deal with a 20-junction 1D array and 4-junction turnstile coupled at their center electrodes via a coupling capacitor. A coupling parameter, Qc, and a current mirror index are introduced to define the strength of coupling and to evaluate the quality of the current mirror effect, respectively. Numerical results show that a finite gate charge of e/2 to the center electrodes of both the 1D array and the turnstile enhances the current mirror effect, where −e is the charge of an electron. To investigate the enhanced current mirror effect, charge propagation in the 1D array under a finite gate charge of e/2 is simulated. It is found that electrons temporarily trapped at the center electrode in the 1D array play an important role in the enhancement of the current mirror effect.

Single-Electron Turnstile Locked to Charge Solitons in a One-Dimensional Array of Small Junctions

We present numerical results on the current mirror effect in a single-electron turnstile capacitively coupled with a one-dimensional (1D) array of small tunnel junctions. Contrary to conventional operation with a sinusoidal signal source, the single-electron turnstile is driven by charge solitons (and anti-solitons) transferred through the 1D array. Then, the current through the turnstile can be locked to the current through the 1D array; this is the current mirror effect. We numerically demonstrate the current mirror effect in our circuit, where a 4-junction turnstile and a 20-junction 1D array are coupled at their middle nodes via a coupling capacitor. We introduce a coupling parameter, Qc, to define the strength of coupling between the 1D array and the turnstile. We also introduce a current mirror index, CMI, to evaluate the quality of the current mirror effect. The dependence of CMI upon the soliton length, the current through the 1D array, and Qc is discussed.

Coulomb blockade threshold in finite one-dimensional arrays of small tunnel junctions: computer simulation

The current–voltage characteristics of one-dimensional tunnel junction arrays are simulated using the semiclassical and full capacitance matrix description. The threshold voltage V th of the Coulomb blockade (CB) is evaluated and analyzed in detail as a function of the gate capacitance C 0, the array length N, the temperature, and the degree of disorder. The disordered effect is found to be essential, while the long range interaction included in the full capacitance matrix calculations, when decreasing V th, weakly affects the qualitative behaviour of the CB for the V th( C 0) and the V th( N) dependences.

A fast, primary Coulomb blockade thermometer

We have measured the third derivative of the current–voltage characteristics, d3I/dV3, in a two-dimensional array of small tunnel junctions using a lock-in amplifier. We show that this derivative is zero at a voltage which scales linearly with the temperature and depends only on the temperature and natural constants, thus providing a primary thermometer. We demonstrate a measurement method which extracts the zero crossing voltage directly using a feedback circuit. This method requires only one voltage measurement, which makes it substantially faster than the original Coulomb blockade thermometry method.

A two-dimensional array of tunnel junctions used for Coulomb blockade thermometry

We have measured current–voltage characteristics of a two-dimensional array of small tunnel junctions at temperatures from 1.4 to 4.2 K. This corresponds to thermal energies larger than the charging energy. We show that 2D-arrays can be used as primary thermometers in the same way as 1D-arrays, and have several advantages over 1D-arrays.

Coulomb blockade thermometry using a two-dimensional array of tunnel junctions

We have measured current–voltage characteristics of two-dimensional (2D) arrays of small tunnel junctions at temperatures from 1.5 to 4.2 K. This corresponds to thermal energies larger than the charging energy. We show that 2D arrays can be used as primary thermometers in the same way as one-dimensional (1D) arrays, and even have some advantages over 1D arrays. We have carried out Monte Carlo simulations, which agree with our experimental results.

A current mirror based on single electron devices

Abstract We have fabricated Coulomb blockade devices which act as current mirrors. Each sample consists of two nominally identical one-dimensional arrays of small tunnel junctions. Each electrode of one array is capacitively coupled to two electrodes in the other array. By measuring the current voltage characteristics of the two arrays simultaneously, we observe a coupling between the currents in the two arrays. We have studied the properties both in the superconducting state and in the normal state, and we interpret the data in terms of correlated transport of charges in the two arrays. The locking between the currents in the two arrays is strongest for intermediate magnetic fields where the electrodes are still superconducting. At best we find current locking over a range of ±6.7 pA

Single Electron Transfer Logic Gate Family

Single electron transfer logic circuits, where logical bit information is represented by the existence of discrete small current pulses accompanied by single electron tunneling (SET) in a one-dimensional array of small tunnel junctions, have been investigated. The basic operation characteristics of several key circuit elements, such as an SET transmission line, a confluence circuit, a split circuit and a set-reset gate were examined and their correct functionality was verified by Monte Carlo simulation. We have shown that basic logic gates, such as NOT, AND and OR, can be implemented using these circuit elements if we provide periodic single electron clock pulses to the gates. Robustness of these logic gates has also been investigated by calculating the dc bias margin.

Slanted coupling of one-dimensional arrays of small tunnel junctions

We have studied the electrostatic problem of the slanted coupling of two one-dimensional (1D) arrays with equal junction capacitances C, equal stray capacitances Co, equal coupling capacitances Cc, and with both arrays biased. In the weak coupling limit (Cc/C≪1), we obtain an analytic solution for the potential profile and the corresponding Gibbs free energy, and we derive threshold voltages for various charge transport modes. Our results show that C0, Cc, and the bias voltage V1 all play important roles in determining the threshold voltage of the system. In the small stray capacitance limit (C0/C≪1), the threshold voltage is proportional to 1/C, while in the large stray capacitance limit (C0/C≫1), the threshold voltage becomes independent of C. Also, in the small Cc/C limit, single electron tunneling always has a lower threshold voltage than that of the electron-hole and mixed tunneling. In addition, we find that V1 has a more dramatic effect on the electron-hole tunneling threshold voltage than on that of the single electron tunneling, i.e., at some favored value of Cc/C a small change in V1 can switch the transport of the system from single electron to electron-hole transport.

Additional Coulomb blockade and negative differential conductance in closed two-dimensional tunnel junction arrays

We have theoretically investigated the transport properties of a two-dimensional array of small tunnel junctions having two different paths between the source and the drain electrodes. We have found that at zero temperature the Coulomb interaction between tunneling electrons in the upper and the lower branches of the array can bring about stationary configurations of electrons which completely block further influx of electrons from the source at voltages above the usual Coulomb blockade. This “additional” Coulomb gap is transformed into a negative differential conductance regime at finite temperature. We also discuss the effect of imperfection of arrays on the additional Coulomb blockade phenomena.

Geometrically Induced Multiple Coulomb Blockade Gaps

We have theoretically investigated the transport properties of a ring-shaped array of small tunnel junctions, which is weakly coupled to the drain electrode. We have found that the long range interaction together with the semi-isolation of the array bring about the formation of stable standing configurations of electrons. The stable configurations break up during each transition from odd to even number of trapped electrons, leading to multiple Coulomb blockade gaps in the $I\ensuremath{-}V$ characteristics of the system.

Shot noise of single-electron tunneling in one-dimensional arrays

We have used numerical modeling and a semi-analytical calculation method to find the low frequency value S_{I}(0) of the spectral density of fluctuations of current through 1D arrays of small tunnel junctions, using the ``orthodox theory'' of single-electron tunneling. In all three array types studied, at low temperature (kT << eV), increasing current induces a crossover from the Schottky value S_{I}(0)=2e<I> to the ``reduced Schottky value'' S_{I}(0)=2e<I>/N (where N is the array length) at some crossover current I_{c}. In uniform arrays over a ground plane, I_{c} is proportional to exp(-\lambda N), where 1/\lambda is the single-electron soliton length. In arrays without a ground plane, I_{c} decreases slowly with both N and \lambda. Finally, we have calculated the statistics of I_{c} for ensembles of arrays with random background charges. The standard deviation of I_{c} from the ensemble average <I_{c}> is quite large, typically between 0.5 and 0.7 of <I_{c}>, while the dependence of <I_{c}> on N or \lambda is so weak that it is hidden within the random fluctuations of the crossover current.

Gate Voltage Dependence of the Resistance of a Two-Dimensional Array of Small Tunnel Junctions

We studied the gate voltage dependence of the resistance of a two-dimensional array of Al/AlOx/Al small tunnel junctions. The resistance exhibited periodic oscillations similar to those in a single electron transistor in both superconducting and normal states. The amplitude of the oscillation in the superconducting state was much smaller than that in the normal state.

Electron-Hole Transport in Capacitively Coupled 1D Arrays of Small Tunnel Junctions

We have measured the current-voltage characteristics of two capacitively coupled 1D arrays of small tunnel junctions, where the coupling capacitance is significantly larger than the junction capacitance. We voltage biased only one of the arrays, while the current was measured simultaneously in both arrays. We find that, at low bias voltages, the currents in the two arrays are comparable in magnitude but opposite in direction. The currents are carried by tunneling electron-hole pairs that are bound by the charging energy of the coupling capacitance.

Chemical Potential Dependence of Resistance of Two-Dimensional Array of Small Tunnel Junctions

Chemical Potential Dependence of Resistance of Two-Dimensional Array of Small Tunnel Junctions

Effect of self-capicitance on charge Kosterlitz-Thouless transition in two-dimensional arrays of small tunnel junctions

We have studied the self-capacitance dependence of zero-bias resistance in two-dimensional arrays of highly resistive small tunnel junctions. All samples showed the square-root-cusp temperature dependence, which is inherent in the precursor of Kosterlitz-Thouless (KT) transition of charge, in a limited temperature range. Deviation from it at lower temperatures is more prominent in arrays with smaller screening length. The results suggest that the finiteness of the screening length is responsible for the disappearance of the charge KT transition in these arrays.