Multi-terminal Configuration Research Articles

Effect of Moderate Electropulsing on Nb Multiterminal Transport Bridges

We investigate targeted and localized material modifications produced by electropulsing of $\mathrm{Al}$-capped $\mathrm{Nb}$ microbridges with a multiterminal configuration. The affected regions of the $\mathrm{Nb}$/$\mathrm{Al}$ bilayer terminals are revealed by an in-lens secondary-electron detector in a scanning electron microscope and by Kelvin-probe force microscopy, both suggesting a decrease in the work function in the modified areas. In contrast, the affected areas are neither apparent through an Everhart-Thornley secondary-electron detector nor through atomic force microscopy, which indicates little morphological change in the microstructure. In addition, we demonstrate that the extent of the electroannealed regions is strongly influenced by the terminal geometry. These results are captured by complementary finite-element modeling, which permits us to estimate that a threshold temperature of $435\ifmmode\pm\else\textpm\fi{}35$ K is needed to induce material modifications. These findings provide further insights into the subtle modifications produced by gentle electroannealing of $\mathrm{Nb}$/$\mathrm{Al}$ microstructures and represent a step forward towards mastering this emerging nanofabrication technique.

Fault Simulations in a Multiterminal High Voltage DC Network with Modular Multilevel Converters Using Full-Bridge Submodules

The concept of high-voltage DC transmission using a multiterminal configuration is presently a central topic of research and investment due to rekindled interest in renewable energy resource integration. Moreover, great attention is given to fault analysis, which leads to the necessity of developing proper tools that enable proficient dynamic simulations. This paper leverages models and control system design techniques and demonstrates their appropriateness for scenarios in which faults are applied. Furthermore, this paper relies on full-bridge submodule topologies in order to underline the increase in resilience that such a configuration brings to the multiterminal DC network, after an unexpected disturbance. Therefore, strong focus is given to fault response, considering that converters use a full-bridge topology and that overhead power lines connect the terminals.

Directional derivative‐based method for quasi‐stationary voltage support analysis of single‐infeed VSC‐HVDC units

This study presents an investigation of the impact of the quasi-stationary voltage support provided by a voltage source converter (VSC) connected to a single point of a power system. Based on the directional derivative concept, an analytical method is developed to quantify the sensitivities of the AC bus voltage with respect to the VSC reactive power control modes. Based on a real case study, it is shown that the method applies to VSC units that are part of VSC-HVDC systems, which can operate in a point-to-point or multi-terminal configuration. Time-domain simulations are performed to verify the findings from the application of the analytical method on a reduced size power system.

Direct Visualization of Current-Stimulated Oxygen Migration in YBa2Cu3O7−δ Thin Films

The past years have witnessed major advancements in all-electrical doping control on cuprates. In the vast majority of cases, the tuning of charge carrier density has been achieved via electric field effect by means of either a ferroelectric polarization or using a dielectric or electrolyte gating. Unfortunately, these approaches are constrained to rather thin superconducting layers and require large electric fields in order to ensure sizable carrier modulations. In this work, we focus on the investigation of oxygen doping in an extended region through current-stimulated oxygen migration in YBa2Cu3O7-δ superconducting bridges. The underlying methodology is rather simple and avoids sophisticated nanofabrication process steps and complex electronics. A patterned multiterminal transport bridge configuration allows us to electrically assess the directional counterflow of oxygen atoms and vacancies. Importantly, the emerging propagating front of current-dependent doping δ is probed in situ by optical microscopy and scanning electron microscopy. The resulting imaging techniques, together with photoinduced conductivity and Raman scattering investigations, reveal an inhomogeneous oxygen vacancy distribution with a controllable propagation speed permitting us to estimate the oxygen diffusivity. These findings provide direct evidence that the microscopic mechanism at play in electrical doping of cuprates involves diffusion of oxygen atoms with the applied current. The resulting fine control of the oxygen content would permit a systematic study of complex phase diagrams and the design of electrically addressable devices.

Intrinsic Photoconductivity of Few-layered ZrS2 Phototransistors via Multiterminal Measurements

We report intrinsic photoconductivity studies on one of the least examinedlayered compounds, ZrS2.Few-atomic layer ZrS2 field-effect transistorswere fabricated on the Si/SiO2 substrate and photoconductivity measurements were performed using both two- and four-terminal configurationsunder the illumination of 532 nm laser source. We measured photocurrentas a function of the incident optical power at several source-drain (bias)voltages. We observe a significantly large photoconductivity when measured in the multiterminal (four-terminal) configuration compared to thatin the two-terminal configuration. For an incident optical power of 90nW, the estimated photosensitivity and the external quantum efficiency(EQE) measured in two-terminal configuration are 0.5 A/W and 120%,respectively, under a bias voltage of 650 mV. Under the same conditions,the four-terminal measurements result in much higher values for both thephotoresponsivity (R) and EQE to 6 A/W and 1400%, respectively. Thissignificant improvement in photoresponsivity and EQE in the four-terminal configuration may have been influenced by the reduction of contactresistance at the metal-semiconductor interface, which greatly impacts thecarrier mobility of low conducting materials. This suggests that photoconductivity measurements performed through the two-terminal configurationin previous studies on ZrS2 and other 2D materials have severely underestimated the true intrinsic properties of transition metal dichalcogenides andtheir remarkable potential for optoelectronic applications.

Hybrid HVDC (H2VDC) System Using Current and Voltage Source Converters

This paper presents an analysis of a new high voltage DC (HVDC) transmission system, which is based on current and voltage source converters (CSC and VSC) in the same circuit. This proposed topology is composed of one CSC (rectifier) and one or more VSCs (inverters) connected through an overhead transmission line in a multiterminal configuration. The main purpose of this Hybrid HVDC (H2VDC), as it was designed, is putting together the best benefits of both types of converters in the same circuit: no commutation failure and system’s black start capability in the VSC side, high power converter capability and low cost at the rectifier side, etc. A monopole of the H2VDC system with one CSC and two VSCs—here, the VSC is the Modular Multilevel Converter (MMC) considered with full-bridge submodules—in multiterminal configuration is studied. The study includes theoretical analyses, development of the CSC and VSCs control philosophies and simulations. The H2VDC system’s behavior is analyzed by computational simulations considering steady-state operation and short-circuit conditions at the AC and DC side. The obtained results and conclusions show a promising system for very high-power multiterminal HVDC transmission.

A Load Flow Analysis for AC/DC Hybrid Distribution Network Incorporated with Distributed Energy Resources for Different Grid Scenarios

With the recent developments in power electronics technologies, increased deployment of distributed energy resources (DER) with DC output type at distribution voltage levels and significant increase in the number of sensitive AC and DC loads integrated in distribution network have enforced the traditional power network in the continuous renovation process. In this paper, the load flow solution of hybrid AC/DC distribution networks with the multi-terminal configuration is studied. The impact of voltage source converter (VSC) losses and AC and DC line losses in the presence of DER in the distribution system are assessed. The motivation of this analysis is to consider an increase in the number of converter stations which might result in non-negligible converter losses and the presence of various DER within the network imposing different network scenarios. The proposed schemes are simulated on two modified IEEE 33 bus hybrid AC/DC distribution network test system equipped with VSC-MTDC and the results are presented. Obtained results show that by considering the network losses and the converter losses with large number of converters within the network could lead to very different load flow solution and power transfer between networks, especially considering the AC or DC bus dominated network.

Impact of converter losses on the optimal power flow solution of hybrid networks based on VSC-MTDC

This paper studies the impact of voltage source converter (VSC) losses on the solution of the optimal power flow (OPF) of hybrid AC/DC systems with a multi-terminal configuration. The motivation of this analysis is that the expected development of high voltage direct current (HVDC) systems will entail an increase of the number of converter stations, and consequently, converter losses might not be negligible when compared with conventional transmission losses of AC and DC lines. Towards this end, an extended OPF model is proposed considering a combination of VSC based multi-terminal HVDC grids (VSC-MTDC) and AC systems. The OPF model represents converter losses according to the state-of-the art modeling where different expressions are used when the converter functions as an inverter or as a rectifier. Three simpler alternative approaches are also implemented and the obtained OPF solutions are assessed. In order to compare the OPF solutions, a comparison metric is proposed. Obtained results show that modeling the converter losses in a simplified way could lead to very different power flow solutions, especially for the DC branches.

Photoconductivity of few-layered p-WSe2 phototransistors via multi-terminal measurements

Recently, two-dimensional materials and in particular transition metal dichalcogenides (TMDs) have been extensively studied because of their strong light–matter interaction and the remarkable optoelectronic response of their field-effect transistors (FETs). Here, we report a photoconductivity study from FETs built from few-layers of p-WSe2 measured in a multi-terminal configuration under illumination by a 532 nm laser source. The photogenerated current was measured as a function of the incident optical power, of the drain-to-source bias and of the gate voltage. We observe a considerably larger photoconductivity when the phototransistors were measured via a four-terminal configuration when compared to a two-terminal one. For an incident laser power of 248 nW, we extract 18 A W−1 and ∼4000% for the two-terminal responsivity (R) and the concomitant external quantum efficiency (EQE) respectively, when a bias voltage Vds = 1 V and a gate voltage Vbg = 10 V are applied to the sample. R and EQE are observed to increase by 370% to ∼85 A W−1 and ∼20 000% respectively, when using a four-terminal configuration. Thus, we conclude that previous reports have severely underestimated the optoelectronic response of transition metal dichalcogenides, which in fact reveals a remarkable potential for photosensing applications.

Thermoelectric efficiency of three-terminal quantum thermal machines

The efficiency of a thermal engine working in the linear response regime in a multi-terminal configuration is discussed. For the generic three-terminal case, we provide a general definition of local and non-local transport coefficients: electrical and thermal conductances, and thermoelectric powers. Within the Onsager formalism, we derive analytical expressions for the efficiency at maximum power, which can be written in terms of generalized figures of merit. Furthermore, using two examples, we investigate numerically how a third terminal could improve the performance of a quantum system, and under which conditions non-local thermoelectric effects can be observed.

Comparative Stability Analysis of Offshore Wind and Marine-Current Farms Feeding Into a Power Grid Using HVDC Links and HVAC Line

This paper presents the comparative stability analyzed results of integration of a doubly fed induction generator-based offshore wind farm (OWF), a PMSG-based OWF, and a squirrel-cage induction generator-based marine-current farm (MCF) feeding into a power grid through a high-voltage alternating-current line and two high-voltage direct-current (HVDC) links. One of the HVDC links is based on a voltage-source converter (VSC) while the other is a multiterminal configuration that uses three VSCs at the converter station and a VSC at the inverter station. A power oscillation damping (POD) controller for the MT-HVDC system is designed, and the design steps include the selection for the POD controller based on the total effects on the remaining system. A frequency-domain approach based on a linearized system model using calculated eigenvalues and a time-domain scheme based on a nonlinear system model subject to disturbances are systematically performed to compare the damping characteristics contributed by the three transmission schemes. It can be concluded from the simulation results that the proposed MT-HVDC link is capable of rendering better damping characteristics to stabilize the integrated OWFs and MCF feeding into a power grid under a severe fault than the HVAC line and the VSC-HVDC link.

Noise properties of thick-film resistors in extended temperature range

Results of thorough experimental studies on electrical properties of thick-film resistors (TFRs) have been overviewed and summarized. Experiments covered resistance and noise measurements in wide temperature range. Low-frequency noise spectroscopy has been used for the investigations of fluctuating phenomena. Sample resistors were prepared of various combinations of commercial and laboratory-made conducting and resistive pastes and printed on alumina substrates. Resistive pastes were made of materials: (i) Pb-containing RuO 2- and Bi 2Ru 2O 7-based, (ii) Pb/Cd-free RuO 2-, CaRuO 3-, and RuO 2/CaRuO 3-based. Conducting pastes included Ag, Ag–Pd and Ag–AgPt–Pd, Au, PtAu as a main ingredients. Electrical properties of various TFRs made of different materials were compared. Cross-correlation technique of noise spectra measurements in conjunction with the multiterminal configuration of TFRs was used in investigations of noise vs. resistor volume, resulting in extraction of noise components originated in different parts of the resistor. Furthermore, noise of the resistor was split up into bulk and interface noise. Resistance noise, observed in all studied TFRs, has been found to consist of background 1/ f noise and Lorentzian noise induced by thermally activated noise sources (TANSs). Properties of TANSs have been described and their relation to TFRs performance parameters have been pointed out. Noise properties of various Pb-containing and Pb/Cd-free resistive materials have been compared with the use of bulk noise intensity parameter, C bulk . Conclusions concerning compatibility of resistive and conductive pastes have been formulated. They might be useful in further improvement of materials systems for thick-film technology in order to fabricate low-noise and stable passives.

Resistance switching in silver – manganite contacts

We investigate the electric pulse induced resistance switching in a transition metal oxide-metal contact at room temperature – a non volatile, reversible and multilevel memory device. Using a simple multiterminal configuration, we find that the complementary effect -in which the contact resistance of each pulsed electrode displays variations of opposite sign- is strongly influenced by the history of the pulsing procedure. Loops performed by varying the magnitude and sign of the stimulus at each pulsed electrode allow to disentangle their sole contribution at different stages of the process. Electromigration of oxygen ions and vacancies is discussed as participating at the core of the underlying mechanisms for resistance switching.

Enhancement of the Supercurrent at a Finite Voltage in a Sandwich-Type Ballistic SINIS Junction

A large, reentrant, Josephson current is observed in SINIS (Nb/Al/AlOx/Al/AlOx/Al/Nb) junctions at a finite voltage close to Delta/e (where Delta is the superconducting energy gap in S) and a bias current exceeding the zero-voltage Josephson current. The effect is studied using a multiterminal device configuration. A theoretical interpretation in terms of quantized electron states in the N layer is provided.

Electrical properties of a single electrochemically template-synthesized polypyrrole nanowire

The electrical properties of a single conducting polypyrrole nanowire, template-synthesized by electrochemical polymerization of pyrrole, were directly measured by the four-terminal technique. Two pairs of microelectrodes were deposited by the focused ion beam system. It is found that the resistivity of the measured nanowire lies in the insulating regime and it follows the one-dimensional Mott variable range hopping model in the temperature range of 77–300K. The conductivity of several segments of another single polypyrrole nanowire was also measured by a multiterminal configuration at room temperature, and it is found that the conductivity is not uniform even on the same nanowire.

Transverse and secondary voltages in Bi2Sr2CaCu2O8 single crystals

Multicontact configuration is one of the most powerful arrangements for electrical transport measurements applied to study vortex phase transition and vortex phase dimensionality in strongly anisotropic high-Tc superconducting materials. In this paper we present electrical transport measurements using a multiterminal configuration, which prove both the existence of guided vortex motion in Bi2Sr2CaCu2O8 single crystals near the transition temperature and that secondary voltage in zero external magnetic field is induced by thermally activated vortex loop unbinding. The phase transition between the bound and unbound states of the vortex loops was found to be below the temperature where the phase coherence of the superconducting order parameter extends over the whole volume of the sample. We show experimentally that 3D/2D phase transition in vortex dimensionality is a length-scale-dependent layer decoupling process and takes place simultaneously with the 3D/2D phase transition in superconductivity at the same temperature.

Length-scale-dependent phase transition in Bi2Sr2CaCu2O8 single crystals

Electrical transport measurements using a multi-terminal configuration are presented, which prove that in Bi2Sr2CaCu2O8 single crystals near the transition temperature in zero external magnetic field the secondary voltage is induced by thermally activated vortex loop unbinding. The phase transition between the bound and unbound states of the vortex loops was found to be below the temperature where the phase coherence of the superconducting order parameter extends over the whole volume of the sample. We show experimentally that 3D–2D phase transition in vortex dimensionality is a length-scale-dependent layer decoupling process and takes place simultaneously with the 3D–2D phase transition in superconductivity at the same temperature.

Spatially resolved resistivity near the vortex lattice phase transition in Bi2Sr2CaCu2O8+δ single crystals

Using a multiterminal contact configuration, we investigate the local variations of the resistivity drop near the vortex lattice first order phase transition in a very homogeneous Bi2Sr2CaCu2O8+δ (BSCCO) single crystal.

Multiterminal source coding achievable rates and reliability

Some open problems concerning classical multiterminal configuration in which two correlated sources {X} and {Y} are encoded separately and decoded by common decoder with respect to a fidelity criterion for messages of both sources are resolved. The results of Berger and Yeung (1989) are expanded in two directions. First, we determine the rate-distortion region R(/spl Delta/) of achievable rates R/sub x/, R/sub y/ for a given /spl Delta/=(/spl Delta//sub x/,/spl Delta//sub y/) with /spl Delta//sub x/ the permissible level for reproduction of X and /spl Delta//sub y/- for Y. Thus we give a full solution of the problem noted by Kaspi and Berger (1982) (they constructed the inner bound for R(/spl Delta/)), and solved by Berger and Yeung for the case of one distortion. Second, we introduce the notion of rate-reliability, distortion region for the multiterminal source encoding problem; more precisely, the region of admissible rates of codes ensuring exponential decrease with a given exponent E>0 of the probability of exceeding the levels /spl Delta//sub x/ or /spl Delta//sub y/. The inner and outer bounds for this region R(E,/spl Delta/) are constructed. The analytical representation obtained for R(/spl Delta/) proved to be somewhat simpler than that considered by Kaspi and Berger and by Berger and Yeung. Ours uses only variables pertaining to the problem statement with no auxiliary ones.

A contact limited precision of the quantized Hall resistance

A four-terminal Hall resistance is analyzed using the Büttiker formalism of contacts. The possible maximum deviation of a quantized Hall resistance from ideal values in a multiterminal device is shown to be limited by the resistances of contacts. A general expression for the possible maximum deviation is derived for a multiterminal configuration with an arbitrary number of terminals in the condition of an arbitrary (integer) number of filled Landau levels. The influence of an inhomogeneous two-dimensional electron gas on the Hall resistance is also discussed.