Large Negative Voltage Research Articles

Electric field induced associations in the double layer of salt-in-ionic-liquid electrolytes.

Ionic liquids (ILs) are an extremely exciting class of electrolytes for energy storage applications. Upon dissolving alkali metal salts, such as Li or Na based salts, with the same anion as the IL, an intrinsically asymmetric electrolyte can be created for use in batteries, known as a salt-in-ionic liquid (SiIL). These SiILs have been well studied in the bulk, where negative transference numbers of the alkali metal cation have been observed from the formation of small, negatively charged clusters. The properties of these SiILs at electrified interfaces, however, have received little to no attention. Here, we develop a theory for the electrical double layer (EDL) of SiILs where we consistently account for the thermoreversible association of ions into Cayley tree aggregates. The theory predicts that the IL cations first populate the EDL at negative voltages, as they are not strongly bound to the anions. However, at large negative voltages, which are strong enough to break the alkali metal cation-anion associations, these IL cations are exchanged for the alkali metal cation because of their higher charge density. At positive voltages, we find that the SiIL actually becomes more aggregated while screening the electrode charge from the formation of large, negatively charged aggregates. Therefore, in contrast to conventional intuition of associations in the EDL, SiILs appear to become more associated in certain electric fields. We present these theoretical predictions to be verified by molecular dynamics simulations and experimental measurements.

Co-regulation of phase-domain structure in Bi0.5Na0.5TiO3- based ferroelectrics to optimize energy storage properties

Sodium bismuth titanate (BNT)-based dielectric capacitors with excellent energy storage performance play an important role in electronics industry. (Sr1.05Bi0.3)ScO3 (SBS) is introduced into 0.85Bi0.5Na0.5TiO3-0.15NaNbO3 (BNT-NN) to achieve co-regulation of phase and domain structure. With the introduction of SBS, the dominated pseudocubic phase accompanied by a small percentage of rhombohedral phase are tend to form, and thus induce nanodomain structure with high-density domain walls. Under the excitation of a bias voltage, the induced nanodomains are easier to switch and effectively reduce the residual polarization. Additionally, the homogeneous nanodomains with high-density domain walls will promote large negative built-in voltage which are favorable to rise of breakdown field strength, and thus, optimize the energy storage performance. The co-regulation of phase-domain structure provides an idea for designing ferroelectrics with good energy storage performance.

Rational design of compact ceramic coating on SiCp/Al composites by tailoring soft sparking discharge of plasma electrolytic oxidation

The characteristics of PEO processes on SiCp/Al composite in aluminate electrolyte under the influence of negative pulse were comparatively investigated, aiming to tailor the soft sparking discharge states, thus achieving the compact ceramic coating and providing a deep understanding of the mechanisms involved. Tracking the variation trend of element optical emission intensity by OES technology reflects the influence of negative voltage on the evolution of the spark state, and the results show that large negative voltage accelerates the transition from arc sparking discharge to soft sparking discharge. When the PEO process completely enters the soft spark discharge state, the lowest electron density can also be kept at 1.06 × 1022 m−3, reaching the local thermodynamic equilibrium condition. At this time, the electron temperature in the plasma discharge zone is about 4000 K. In addition, the coating surface roughness value decreases with the increase of negative voltage, and the introduction of negative voltage effectively reduces the irregular convex structures and the macropores in the coating, due to inhibiting destructive high-intensity spark discharge by the soft sparking discharge.

An asymmetric-square-wave voltage injection method for online inductance identification of PMSM under sensorless control

In this paper, an online inductance identification method for PMSM, which is embedded into the flux-estimation-based sensorless control, is proposed. By injecting a periodic voltage where a larger negative voltage lasts one switching cycle, and a smaller positive voltage lasts several switching cycles, the extra voltage equation is established. Then, the q-axis current can be decomposed to an asymmetric triangular wave component and a low frequency component. Using the triangular wave current and the voltage equation, an inductance identification algorithm is designed. Since the injected positive voltage can be smaller, this method overcomes the difficulty that the symmetric square wave voltage cannot be injected at high-speed range, thus expanding the application of the inductance identification. And since the triangular wave current can be accurately extracted, the interference caused by back-EMF is eliminated. The simulation results demonstrate the effectiveness of the method.

Study of dielectric breakdown in liquid xenon with XeBrA: The xenon breakdown apparatus.

Maintaining the electric fields necessary for the current generation of noble liquid time projection chambers (TPCs), with drift lengths exceeding 1m, requires a large negative voltage applied to their cathode. Delivering such high voltage is associated with an elevated risk of electrostatic discharge and electroluminescence, which would be detrimental to the performance of the experiment. The Xenon Breakdown Apparatus (XeBrA) is a 5-l, high voltage test chamber built to investigate the contributing factors to electrical breakdown in noble liquids. In this work, we present the main findings after conducting scans over stressed electrode areas, surface finish, pressure, and high voltage ramp speed in the medium of liquid xenon. Area scaling and surface finish were observed to be the dominant factors affecting breakdown, whereas no significant changes were observed with varying pressure or ramp speed. A general rise in both the anode current and photon rate was observed in the last 30s, leading up to a breakdown, with a marked increase in the last couple of seconds. In addition, the position of breakdowns was reconstructed with a system of high-speed cameras and a moderate correlation with the Fowler-Nordheim field emission model was found. Tentative evidence for bubble nucleation being the originating mechanism of breakdown in the liquid was also observed. We deem the results presented in this work to be of particular interest for the design of future, large TPCs, and practical recommendations are provided.

An on-chip integrated current sensor with high precision and large current range for smart power ICs

This work presents a precision current sensor with a high gain amplifier. Three aspects are improved. Firstly, the gain boosting is achieved by adding nested-amplifiers, namely AMPH and AMPL. Secondly, the DC error is eliminated by implementing a cascode current mirror branch with bias current compensation. Thirdly, the damage of large negative overshoot voltage to the operational amplifier is avoided because of the inserted switch transistors disconnecting the amplifier from load. For the ratio of main-FET to sense-FET, a factor of M = 5000 is chosen to keep the power consumption low. Measurement results show that this current sensor can operate from −60 °C to 120 °C with supply voltage from 10 V to 30 V. The measured absolute error between the sensed signal and the load current is less than 3% in range of 20 mA to 3.6 A at 27 °C. This current sensor has been fabricated in a 0.5 μ m SOI BCD process, which can be applied in smart power ICs.

Detection of defect levels in vicinity of Al2O3/p-type GaN interface using sub-bandgap-light-assisted capacitance–voltage method

Defect levels in the vicinity of the Al2O3/p-type GaN interface were characterized using a sub-bandgap-light-assisted capacitance–voltage (C–V) method. For metal–oxide–semiconductor (MOS) diodes prepared using p-type GaN (p-GaN) and Al2O3 formed by atomic layer deposition, the C–V curves measured in the dark showed capacitance saturation at a negative bias and a large negative voltage shift compared with ideal curves, which implied the effects of donor-like gap states in the vicinity of the Al2O3/p-GaN interface. Upon illumination with monochromated sub-bandgap light with photon energies higher than 2.0 eV under a large positive bias, the subsequently measured C–V curves showed three plateaus. The plateau under the positive bias voltage due to the surface inversion appeared despite the sub-bandgap illumination, which did not appear at 1.8 eV light illumination, indicating the existence of midgap defect levels. Moreover, the other plateaus were attributed to defect levels at 0.60 and 0.7–0.8 eV above the valence band maximum. For a sample whose surface was prepared by photo-electrochemical (PEC) etching to a depth of 16.5 nm, the C–V curve measured in the dark showed a reduced voltage shift compared with the unetched sample. Furthermore, sub-bandgap-light-assisted C–V curves of the sample with PEC etching showed no plateau at a positive bias, which indicated the reduction in the density of the midgap defect states. Possible origins of the detected defect levels are discussed. The obtained results showed that the interface control can improve the properties of p-GaN MOS structures.

Cryogenic-temperature investigation of negative bias stress inducing threshold voltage instabilities on 4H-SiC MOSFETs

We investigate the effect of Negative-Bias-Temperature-Instability on 4H-Silicon Carbide MOSFETs at room and cryogenic temperature and found a large negative threshold voltage shift at T < 250 K. For T < 140 K, both capture and emission follow an almost ideal exponential transient. Cryogenic temperatures reveal fast interface traps, otherwise difficult to probe at relatively high temperatures; we attribute the threshold voltage shift to a high density of hole traps located: 1) close to the SiC valence band and able to emit within the measurement time window; 2) above the SiC valence band, responsible of the slow transient at low temperature. Finally, the extraction of the emission time constant via Capture Emission Time map analysis allowed to extract the activation energy of mechanism 2 (82 meV).

Probing the charge and heat transfer channels in optically excited graphene — transition metal dichalcogenide hybrids using Johnson noise thermometry

Graphene (Gr)–transition metal dichalcogenide (TMDC) hybrids are promising platforms for achieving sensitive and ultra-fast photodetection. The process of photo-detection in such van der Waals hybrids is usually dictated by the formation of excitons followed by the transfer of charge and energy from the TMDC layer to graphene, but they have not been explored simultaneously in the same device before. In this work, we have investigated optically excited Gr–WS2 (tungsten disulfide) heterostructures using both standard electrical transport and Johnson noise thermometry. At large negative gate voltages, the experimentally observed photoresponse cannot be explained from conventional photogating but was found to host an increase in electron temperature as large as ∼4 K. Time dependence of the transport and the noise reveals that the change in temperature and photoresistance can originate from distinct microscopic processes. The findings can be exploited for the development of Gr–TMDC based ultra-fast bolometers.

Effects of applying external voltage on development of anaerobic dynamic membrane under high suspended solids conditions

Maintaining proper dynamic membrane (DM) thickness and structure is the key factor for effective filtration and biomass retention in DM bioreactors. This study investigated the effects of negative and positive applied voltages on the development and characteristics of anaerobic DM under high suspended solids conditions. The DM filtration experiments with anaerobic sludge were performed using submerged DM modules with stainless steel support material at applied voltages of –1.2 to +1.2 V. Negative applied voltage (i.e., cathodic DM) delayed the DM fouling, while positive applied voltage (i.e., anodic DM) accelerated the DM growth, within certain voltage ranges by the combined effect of electrostatic forces and electrochemical reactions. Too large negative or positive voltages caused electrochemical corrosion of support material and precipitation of mineral scales, resulting in serious chemical fouling. The cathodic and anodic DMs formed at different applied voltages achieved high suspended solids rejection efficiencies of 86.4–89.6%. The applied voltage had a significant effect not only on the DM growth and filtration resistance but also the surface morphology, cell viability (live/dead cell ratio), and extracellular polymeric substances distribution of DM. Cell damage by electrochemically formed reactive species was observed at high electrode potentials. The overall results suggest that applying external voltage within an appropriate range can be an effective way to control the DM development. Although much more research is needed, the findings of this study offer a new possibility to improve the feasibility of DM technology and its applicability in anaerobic DM bioreactors.

Decoder-Type Scan Driver Suitable for Flexible and Stretchable Displays

The integration of a scan drive circuit is required for flexible and stretchable displays because a rigid scan driver IC is not flexible and stretchable. In this study, decoder-type scan drivers were developed using amorphous IGZO thin-film transistors for both depletion and enhancement mode TFTs. Simulations and measurements show that the proposed decoder-type scan driver operates well for both the enhancement and depletion-mode TFTs without error. The measurement results show that the proposed circuit provides scan pulses well, even with depletion-mode TFTs with a large negative threshold voltage of around −25 V.

High Annealing Stability of InAlZnO Nanofiber Field-Effect Transistors with Improved Morphology by Al Doping.

In2O3 nanofibers usually suffer a high off-current and consequent low on/off current ratio, as well as a large negative threshold voltage (Vth). Furthermore, regarding Zn doped binary-cation In2O3 nanofibers, severe thermal diffusion of Zn elements can result in deteriorated electrical performance when annealed at high temperature. Here, we applied an electrospinning technique to obtain ternary-cation IAZO nanofibers with controllable Vth and chemical stoichiometry. The presence of the Al element in IAZO nanofibers can lead to more superior microstructure with improved uniformity, lower surface defect, and superior metal-oxide-metal lattice at high annealing temperature. Consequently, our Al-doped ternary-cation IAZO devices exhibited an improved on/off current ratio of 107 and a high electron mobility of ∼10 cm2 V-1 s-1. Moreover, the electron mobility can be increased to 30 cm2 V-1 s-1 in our low-voltage operated FETs with high-k AlOx as the dielectric layer, which can be envisioned to exhibit vast implications for high-performance transparent electronics.

Multipurpose Drivers for MEMS Devices Based on a Single ASIC Implemented in a Low‐Cost HV CMOS Process without a Triple Well

This paper presents a novel topology for multipurpose drivers for MEMS sensors and actuators, suitable for integration in low‐cost high‐voltage (HV) CMOS processes, without a triple well. The driver output voltage, VMEMS, can be programmed over a wide, symmetrical range of positive and negative values, with the maximum output voltage being limited only by the maximum drain‐source voltage that the HV transistors can handle. The driver is also able to short its output to the ground line and to leave it floating. It comprises generators for large positive and negative voltages followed by an LDO for each polarity that ensures that VMEMS has a well‐controlled level and a very low ripple. The LDOs also help implement the grounded‐ and floating‐output operating modes. Most of the required circuitry is integrated within a HV CMOS ASIC: the drivers for the large voltage generators, the error amplifiers of the LDOs, the DAC used to program the VMEMS level, and their support circuits. Thus, only the power stages of the large voltage generators, the pass transistors of the LDOs and two resistors for the LDO feedback network are discrete. A suitable configuration was devised for the latter that allows for the external resistor network to be shared by the two LDOs and prevents negative voltages from developing at the ASIC pins. Two circuit implementations of the proposed topology, designed in a low‐cost 0.18 μm HV CMOS process, are presented in some detail. Simulation results demonstrate that they realize the required operating modes and provide VMEMS voltages programmable with steps of 100 mV or 200 mV, between ‐20 V and +20 V or between −45 V and +45 V, respectively. The output voltage ripple is relatively small, just 3.4 mVpkpk for the first implementation and 17 mVpkpk for the second. Therefore, both circuits are suitable for biasing and controlling a wide range of MEMS devices, including MEMS mirrors used in applications such as endoscopic optical coherence tomography.

High-performance field effect transistors based on large ratio metal (Al、Ga、Cr) doped In2O3 nanofibers

Indium oxide nanofibers (In2O3 NFs) are considered to be one of the possible channel materials for future electronic devices, however, these NFs devices suffer from low on/off current ratio (Ion/Ioff), large negative threshold voltage (VTH), and high leakage current due to the excess carriers in NFs. A facile one-step electrospinning technique is employed to synthesize metal element (aluminum (Al), chromium (Cr) or gallium (Ga)) highly-doped In2O3 NFs to both improve the electrical performance of the NFs field effect transistors (FETs) and reduce the consumption of indium. The devices exhibit optimal performance at 10 mol% doping concentration (Al, Cr and Ga): small and positive VTH (<6.0 V), large Ion/Ioff (∼108), high saturation current (∼10−4 A), and decent carrier mobility (∼2.0 cm2/V−1s−1). When a high-k AlOx thin-film is employed as the gate dielectric for the NFs FETs (10 mol% Al–In2O3 NFs), the gate voltage and drain voltage is reduced to 5 V and 3 V, respectively, and the μfe is increased by 6X. Furthermore, 10 mol% Al–In2O3 NFs FETs with enhancement-mode operation were integrated into highly efficient NMOS inverters. All the results indicate that the highly metal-doped In2O3 NFs have practical application for next-generation low-cost, large-area, energy-efficient and high-performance nanoelectronic devices.

Time-resolved Langmuir probe diagnostics of a bipolar high power impulse magnetron sputtering discharge

High power impulse magnetron sputtering (HiPIMS) of a cobalt cathode in argon gas was investigated by time-resolved electrical (Langmuir) probe diagnostics and by time-integrated energy-resolved mass spectrometry. The HiPIMS discharge was operated with a bipolar pulsed power supply, providing a large negative voltage with a typical pulse width of 100 μs followed by a long positive pulse with a pulse width of about 310 μs. The time-resolved Langmuir probe results yield a small negative plasma potential in the negative pulse regime and a large positive floating potential and plasma potential in the positive pulse regime. The electron density is significantly reduced during the positive pulse regime. The probe results are supported by ion energy measurements.

Bound Electron Pairs Formed by the Spin–Orbit Interaction in 2D Gated Structures

The bound electron pairs (BEPs) arising due to the pair spin–orbit interaction (PSOI) in 2D structures are explored with a gate that allows the BEPs to be manipulated. The gate breaks the in‐plane reflection symmetry of the pair Coulomb field and creates a one‐particle Rashba spin–orbit interaction. It is found that the normal component of the electric field substantially affects the BEPs but the key role in forming the BEPs belongs to the in‐plane component. The ground state of a BEP with zero total momentum, which is doubly degenerate in the absence of the gate, splits into two states. One of them is tunable by varying the gate voltage, whereas the other is on the contrary robust. The tunable BEP has a higher binding energy which grows as the gate voltage increases, with its orbital and spin structure changing continuously. At large negative voltage, the tunable BEP decays. The orbital and spin structure of the robust BEP does not depend on the gate voltage. Its energy level crosses the conduction band bottom at high gate voltage of any polarity, but the robust BEP remains bound and localized even when in continuum.

Design options for implementing in standard CMOS drivers for MEMS body biasing

This paper presents design options and transistor-level solutions for implementing, in CMOS processes without triple-well, drivers suitable for MEMS body biasing. The output voltage of the driver envisaged here can be set to positive or negative levels, programmable between (+10 ​V to +20 ​V), respectively (−20 ​V to −10 ​V), with a resolution of 100 ​mV. Also, the driver can ground its output terminal, as well as leave it open/floating, all under digital control. The key parts of such a driver are the voltage generators that provide positive and negative voltages several times larger than the supply voltage and the output stage that delivers the voltage required to bias the MEMS body terminal, VMEMS. Three solutions, which consist of driver topology and circuit implementation of key elements, are proposed and analyzed comparatively. The first solution requires the development of one ASIC that comprises a 9-bit DAC, as well as drivers for the digitally-programmable voltage generators – a boost DC-DC converter and an inverting (negative output voltage) charge pump – which provide directly the wanted positive or negative VMEMS voltage levels, while the output stage is a voltage multiplexer implemented with high-voltage external transistors. The second solution requires two ICs that operate at different substrate voltage levels: an ASIC comprising the same DAC but simpler drivers for more compact, but less accurate, voltage generators. This time, the large positive and negative voltages are only used to supply the output stage of the system. Two options are presented for the later: an off-the-shelf IC and an ASIC that implements a single-OpAmp differential amplifier with positive/negative gain set digitally. The third solution is a more versatile version of the same approach, whereby the first ASIC implements only the positive and negative voltage generators that supply the second ASIC, which comprises a 7-bit DAC and a digitally configurable amplifier. One instance of the first ASIC can supply multiple instances of the second ASIC that operate in parallel, under common or individual control. Proof-of-concept implementations of the proposed ASICs were designed in a high-voltage 0.18 ​ ​μm CMOS process without triple well; schematics of key blocks are presented in the paper. Simulation results validate the design, demonstrating that it is indeed possible to implement in standard CMOS all the circuit functions mentioned above, while reducing the number of external components to a minimum.

Total-Ionizing-Dose Effects in InGaAs MOSFETs With High-k Gate Dielectrics and InP Substrates

The total-ionizing-dose (TID) response of indium gallium arsenide (InGaAs) MOSFETs with Al2O3 gate dielectrics and several channel lengths is evaluated under different biases. DC static characteristics show large negative threshold voltage $V_{\text {th}}$ shifts and subthreshold stretchout ( SS ), indicating net positive charge trapping in the gate oxide and generation of the interface and border traps. Hysteresis and $I_{d}$ – $V_{\text {gs}}$ measurements from cryogenic to high temperatures show the important role of defects in the Al2O3 gate dielectric to the TID response. Radiation-induced-hole trapping is attributed to oxygen vacancies in the Al2O3. The relatively large hysteresis in these devices is attributed primarily to dangling Al bonds in the near-interfacial Al2O3. Analysis of the temperature dependence of $V_{\text {th}}$ and SS suggests that the rate at which electrons leave the Al2O3 during a positive-to-negative gate-bias sweep is higher than the rate at which they enter during a negative-to-positive gate-bias sweep.

Time-resolved optical emission spectroscopy of a unipolar and a bipolar pulsed magnetron sputtering discharge in an argon/oxygen gas mixture with a cobalt target

Reactive high power impulse magnetron sputtering (HiPIMS) of a cobalt cathode in pure argon gas and with different oxygen admixtures was investigated by time-resolved optical emission spectroscopy (OES) and time-integrated energy-resolved mass spectrometry. The HiPIMS discharge was operated with a bipolar pulsed power supply capable of providing a large negative voltage with a typical pulse width of 100 μs followed by a long positive pulse with a pulse width of about 350 μs. The HiPIMS plasma in pure argon is dominated by Co+ ions. With the addition of oxygen, O+ ions become the second most prominent positive ion species. OES reveals the presence of Ar I, Co I, O I, and Ar II emission lines. The transition from an Ar+ to a Co+ ion sputtering discharge is inferred from time-resolved OES. The enhanced intensity of excited Ar+* ions is explained by simultaneous excitation and ionisation induced by energetic secondary electrons from the cathode. The intensity of violet Ar I lines is drastically reduced during HiPIMS. Intensity of near-infrared Ar I lines resumes during the positive pulse indicating an additional heating mechanism.

Use of Discharge Resistor to Improve Transient De-Excitation in Brushless Synchronous Machines

The discharge resistor is only used in case of electrical trip to reduce the field current as fast as possible and to minimize the damages produced by the short-circuit current supplied by the synchronous machine. The connection of the discharge resistor is done by opening the field breaker and it implies a large negative voltage in the field winding. This negative voltage is limited to 80% of the winding insulation voltage. On the other hand, in case of a transient de-excitation, at the first moment, the automatic voltage regulator (AVR) reduces the field voltage to the minimum. In case of one-quadrant rectifier type AVR, the minimum voltage is zero and in case of two-quadrant rectifier AVR, the minimum voltage is close to the ceiling voltage with negative polarity. In both cases, the minimum voltages are much smaller than the negative voltage produced by the connection of the discharge resistor. This paper presents a new system that improves the transient de-excitation of synchronous machines using the discharge resistor by an additional static field breaker (SFB). The control of the static field breaker and consequently the connection and disconnection of the discharge resistor is done based on the output field voltage supplied by the AVR. This allows the exciter field current to be reduced in a faster way and continue with the normal operation of the machine after the transient. In this study, the correct operation of the additional static field breaker (SFB) has been validated by computer simulations and experimental test in a 15 MVA generator comprising a commercial one-quadrant rectifier AVR type obtaining excellent results.