DC Charging Research Articles

Single charge sensing and transport in double quantum dots fabricated from commercially grown Si/SiGe heterostructures

We perform quantum Hall measurements on three types of commercially available modulation-doped Si/SiGe heterostructures to determine their suitability for depletion gate defined quantum dot devices. By adjusting the growth parameters, we are able to achieve electron gases with charge densities 1–3 × 1011/cm2 and mobilities in excess of 100 000 cm2/Vs. Double quantum dot devices fabricated on these heterostructures show clear evidence of single charge transitions as measured in dc transport and charge sensing and exhibit electron temperatures of 100 mK in the single quantum dot regime.

Proposal of evaluation test method for withstand performance under residual DC charge at GIS insulator

AbstractIn recent years, compact gas‐insulated switchgear (GIS) has been developed by rationalization of specifications. All of the GIS have been checked for passage of the AC and lightning impulse (LI) withstand test, but DC stress that occurs on an AC GIS spacer when switching devices are operated has not been sufficiently investigated. Since the electrical field strength inside a GIS tank is stronger in compact GIS, it is increasingly necessary to evaluate the withstand performance of GIS spacers under residual DC voltage. Under DC stress, electrification strengthens the electrical field strength at the creepage surface (Et) and the withstand performance of GIS spacers depends on the maximum value of Et (Etmax). When the volume resistivity at the surface layer of spacer is uneven, Et strengthens at the uneven spots. In this paper, Etmax under DC stress with uneven volume resistivity at the surface layer of the spacer is investigated, and an evaluation test method for withstand performance under residual DC charge is constructed. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 179(1): 21–28, 2012; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.21233

Dielectric properties of solid solutions (1 − x)(KBi)1/2TiO3-xNa1/4Bi3/4Fe1/2Ti1/2O3 near the morphotropic phase boundary

The dielectric properties of solid solution ceramics (1 − x)(KBi)1/2TiO3-(x/2)(NaBi)1/2TiO3-(x/2)BiFeO3 near the morphotropic phase boundary lying near x = 0.75 and separating the compositions with the orthorhombic (x 0.75) structures have been studied. The solid solutions are shown to undergo a diffuse phase transition with the Curie temperature TC = 640–650 K. Based on an analysis of the frequency dependence of the imaginary component of the electric modulus in the range T > TC, it is concluded that the transition of the system of solid solutions near the morphotropic phase boundary (x = 0.75) to the dipole-ordered state is accompanied by the formation of heterophase microregions with different relaxation times of the dielectric polarization. The activation energies of the relaxation of the dielectric polarization (ΔEM) in the aforementioned temperature range and of the dc charge carriers (ΔEdc) are determined. It is found that ΔEdc stepwise increases near 570 K in going toward higher temperatures. It is shown that the behavior of the characteristics of the dielectric response of the solid solutions below 400 K corresponds to a relaxor ferroelectric. For the compositions 0.7 ≤ x ≤ 0.8, the estimated freezing temperature of dipole clusters of the relaxation state is about 240 K, and their activation energy decreases with increasing x.

Biomolecular and electrochemical charge detection by a micromechanical electrometer

A micromechanical electrometer is applied to the label-free detection of biomolecular interactions and electrochemical charge sensing. The primary element of the electrometer is a micromechanical variable capacitor to modulate and convert a dc charge to an ac voltage output, thereby limiting the effects of low frequency noise on charge detection. At room temperature and ambient pressure the noise-limited charge resolution of a micromechanical electrometer based on this principle is found to be 3 e/ Hz , enabling the potential detection of charged single molecule binding on electrode surfaces. The detection principle is validated by several experiments. Biomolecular binding experiments are conducted on an external gold electrode situated within a custom-designed flow cell and electrically connected to the micromachined electrometer. The concepts are validated by demonstrating the detection of biotin–streptavidin binding and DNA hybridization. Furthermore, it is shown that the electrometer can be applied for the detection of the redox system ferrocyanide/ferricyanide to describe Nernstian behaviour due to well defined charge transfer on the electrode surface at different concentration ratios as expected.

Investigation on hot-carrier-induced degradation of SOI NLIGBT

The hot-carrier-induced (HCI) degradations of silicon-on-insulator (SOI) lateral insulated gate N-type bipolar transistor (NLIGBT) are investigated in detail by DC voltage stress experiment, TCAD simulation and charge pumping test. The substrate current I sub and on-state resistance Ron at different voltage stress conditions are measured to assess the HCI effect on device performance. The electric field and impact ionization rate are simulated to assist in providing better physical insights. And charge pumping current is measured to determinate the front-gate interface states density directly. The degradation mechanisms under different gate voltage stress conditions are then presented and summarized.

Dielectric properties of perovskite ceramics of (1–x)BiFeO3 − x(KBi)1/2TiO3 (0.40 < x < 0.85) solid solutions from impedance spectroscopy data

The dielectric properties of the ceramics of (1 − x)BiFeO3 − x(KBi)1/2TiO3 (0.40 < x < 0.85) solid solutions with an orthorhombic structure have been studied using impedance spectroscopy in the frequency range 25–106 Hz at different temperatures. It has been shown that these solid solutions undergo a diffuse ferroelectric phase transition. The Curie temperature is found to be in the range 620–640 K. The activation energies of dielectric polarization relaxation (δEM) and dc charge carriers (ΔEdc) are determined. It has been established that, in the vicinity of 460 K, ΔEdc increases jumpwise as the temperature increases.

Two-Phase Flow Regimes and Discharge Characteristics of a Plasma Electrohydrodynamic Atomization

Experimental investigation was conducted to study the flow regimes and discharge characteristics of plasma electrohydrodynamic atomization (EHDA) for decane (C10H22) under pulsed applied negative voltage. The experimental parameters were set as the flow rate of decane from 0 mL/min to 10 mL/min and the DC charging voltage from DC 0 V to 12 V with a pulse repetition rates of 200 Hz. The flow regime of decane was observed and the volume-to-electrical charge ratio was measured. Unlike a conventional EHDA system, the results show that a corona discharge was initiated at the edge of the hollow electrode at a specific corona on-set voltage of −17 kV or −20 kV in the case with or without decane flow, respectively. This phenomenon was defined as plasma EHDA.

Analysis and control of self-excited induction generator-converter systems for battery charging applications

A method has been developed for the analysis of operation of self-excited induction generators (SEIGs) supplying battery charging loads through three-phase semi-converters by representing the battery circuit as equivalent resistance and reactance in the equivalent circuit of these generators. Such equivalent values are functions of the dc charging voltage and current and the control angle set in the converter. The solution for this circuit has been carried out using the genetic algorithm technique instead of using higher-order polynomials for the loop or nodal equations of the circuit. Apart from the conventional phase angle control, other firing control schemes namely negative firing angle control, extinction angle control and symmetrical angle control have been considered for the operation of the converter. The relative performance of these control schemes, for the various modes of operation of SEIG-converter systems such as constant and variable speed, has been brought out. Experimental results obtained on a three-phase SEIG charging suitable batteries through an IGBT-based semi-converter, controlled with all these schemes, confirm the usefulness of the proposed system and the validity of its analysis.

Realization of polymer charge pump circuits using polymer semiconductors

Vertical diodes made of chromium/gold/poly(3-hexylthiophene) (P3HT)/aluminum are used to implement AC–DC charge pump circuits. A single stage polymer charge pump with 470 nF capacitors is able to supply 7.2 V DC to a load of 1 MΩ || 20 pF when an AC signal with a peak value of 10 V is applied. The circuit can be used up to 10 kHz. High turn-on voltages and internal resistances and capacitances of the diodes limit the DC output voltages. The ramp-up time of the circuit built with 10 nF capacitors is 9.4 ms for a 1 kHz, 10 V peak AC signal. Diodes are modeled and simulated in SPICE using space charge limited conduction model. The simulated charge pump circuit produces consistent results with measurements. Performances of air exposed vertical diodes deteriorate under vacuum, prolonged operation at atmospheric conditions and electrical bias stress resulting in blistering, emphasizing the importance of packaging the devices under inert atmosphere. The DC output voltage and the input impedance of the circuit can be adjusted by using multiple stages.

Analysis and design of power efficient semi-passive RFID tag

The analysis and design of a semi-passive radio frequency identification (RFID) tag is presented. By studying the power transmission link of the backscatter RFID system and exploiting a power conversion efficiency model for a multi-stage AC–DC charge pump, the calculation method for semi-passive tag's read range is proposed. According to different read range limitation factors, an intuitive way to define the specifications of tag's power budget and backscatter modulation index is given. A test chip is implemented in SMIC 0.18 μm standard CMOS technology under the guidance of theoretical analysis. The main building blocks are the threshold compensated charge pump and low power wake-up circuit using the power triggering wake-up mode. The proposed semi-passive tag is fully compatible to EPC C1G2 standard. It has a compact chip size of 0.54 mm2, and is adaptable to batteries with a 1.2 to 2.4 V output voltage.

Pumped charge and spin current in a quantum dot molecule

The effects of an ac electric field on the quantum transport behaviors in a parallel-coupleddouble quantum dot system are investigated theoretically. A dc charge current can bepumped at zero bias due to photon-assisted tunneling effects. The sign, magnitude andposition of the pumped current peaks can be well controlled and manipulated by simplyvarying the gate voltage, the amplitude and frequency of the ac field. Furthermore, thepossibility of electrically pumping a pure spin current in the presence of spin–orbitinteraction is discussed.

24.1: A Vertical Common Electrodes Structure for High Aperture Ratio and Stable IPS Mode TFT‐LCD

AbstractWe developed In‐Plane‐Switching (IPS) mode structure with vertically aligned common electrodes for amorphous silicon (a‐Si) thin film transistor liquid crystal display (TFT‐LCD). We could improve an aperture ratio of the panel with this new structure by the elimination of storage area and compact design. The new vertical structure showed stabilized voltage ripple, DC charge and flicker variation by RC delay reduction and direct voltage driving from every driver IC. The panel was fabricated with the conventional a‐Si TFT process. We focused on making a new structure to get better quality of image compared to previous IPS mode TFT‐LCD.

Insulation resistance under DC stress and electrification characteristics of GIS epoxy insulator

AbstractGas‐insulated switchgear (GIS) has widely been used for AC power distribution because of its high reliability and compactness. Recently, DC GIS has been developed with various investigations for dielectric breakdown characteristics of DC gas insulation. GIS insulation is composed of SF6 gas and solid spacers, and it has been recognized that the dielectric performance of DC GIS is mainly influenced by solid spacers. Under DC stress, the electric field is directed one way, the effect of electrification for charges to be accumulated in the spacer must be taken into account and also the effect exists in AC GIS because the switching operations may leave the remnant DC charge on the AC GIS spacer. This paper first describes the effective resistivity (the bulk or the surface) of the solid spacer under the DC stress from the experimental investigation, and the critical factor on the solid spacer that causes reduced dielectric performance of the GIS insulation is studied. Second, the present paper deals with the electrification on the GIS with various levels of surface roughness of the epoxy insulator and metallic electrode. Finally, the DC insulation characteristics of GIS insulator are investigated based on the experimental results. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 168(4): 6–13, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20788

Electric-field induced spin textures in a superlattice with Rashba and Dresselhaus spin-orbit coupling

The DC charge current, field-induced spin polarization and spin textures are studied in the 1D gated superlattice with both fixed and varying Rashba and Dresselhaus contributions to spin-orbit coupling. It is found that a spin component with zero mean value can demonstrate non-vanishing field-induced spin texture in a superlattice cell which can be probed experimentally, with the highest amplitudes achievable in an interval of comparable Rashba and Dresselhaus terms. The consideration of the finite parameters for collision rate and temperature is found to be non-destructive for the calculated current and spin characteristics depending on all states below the Fermi level.

Charge Transfer and Charge-Discharge Kinetics in Lithium-ion Batteries

Charge transfer and charge-discharge kinetics of practical Li-ion cells were investigated using AC impedance and DC pulse methods. Preliminary AC impedance results indicated that the activation energy for charge transfer for high power Li-ion cells employing carbonate-linear ester solvent mixtures was similar to that for cells employing carbonate solvents as reported before. At 100 milliseconds (ms), the pulsed DC impedance indicated that the charge and discharge kinetics were fast and at about the same rate. At 15 seconds (s), the pulsed DC charge resistance was apparently higher than the discharge resistance especially at temperatures below -20 oC. The slower charging kinetics may be limited by the electron transfer step including intercalation and diffusion of Li into the carbonaceous anode.

Using Portable Media Players (iPod) to Support Electronic Course Materials During a Field-based Introductory Geology Course

Electronic course materials, such a videos, PowerPoint presentations, and animations, have become essential educational tools in classroom-based geoscience courses to enhance students' introduction to basic geological concepts. However, during field trips, the ability to offer students these electronic conceptual supports is lacking where students and faculty are often without access to the electrical grid. The video iPod offers an inexpensive and reliable means by which to provide students access to a wide range of electronic course materials during field trips. GeoJourney, a nine-week field-based interdisciplinary introductory geoscience program at Bowling Green State University, is the first geology field program to use the entire range of the video iPod's capabilities to support electronic course materials while in the field. A video iPod was issued to each student at the beginning of the program, along with a battery back-up and a DC charging cable which was plugged into a custom wiring harness installed in the transport vehicles. Students were able to use the iPods during travel time, in the field on hikes and projects, and in their tents at night. Types of materials included videos, still images, animations, text, audio files, and enhanced podcasts. Students' response to the use of the iPods is overwhelmingly positive and suggest their use on GeoJourney also reduces ‘novelty space’.

Microstructure, electrical properties and Hall coefficient of europium-doped Li–Ni ferrites

Europium-doped Li–Ni soft ferrites with the general formula of (Li 0.5Fe 0.5) 0.5 Ni 0.5Eu y Fe 2− y O 4 (where 0 ≤ y ≤ 0.1), were prepared by using powder processing technique. The effect of Eu addition on the AC and DC electrical resistivity, Hall coefficient, charge mobility and charge carrier concentration of the prepared ferrites were characterized at room temperature. Seebeck coefficient was also calculated from the carrier concentration. Hall and Seebeck coefficients confirmed that all of the prepared samples are p-type semiconductors. The formation of the single-phase spinel ferrites structure was verified by X-ray diffraction. Lattice parameter, X-ray density, apparent density and A- and B-sites radii were calculated. The microstructure, which plays an important role in determining electrical properties, was analyzed by scanning electron microscopy and EDS, and found to have a major effect on the electrical properties. The dielectric loss was calculated from the AC conductivity and found to increase with firing temperature. This study provides information to optimize the composition and microstructure of the europium-doped Li–Ni ferrite with desired performance.

ＧＩＳ絶縁スペーサの直流残留電荷に対する耐圧性能評価試験法の提案

In recent years, compact size gas insulated switchgear (GIS) has been developed from rationalization of specifications. All of the GISs have been checked to pass the AC and lightning impulse (LI) withstand test, however, DC stress that occurs on the AC GIS spacer when switching devices are operated has not investigated enough. Since electrical field strength for inside of GIS tank is more strengthen for compact size GIS than ever, it is more necessary to evaluate the withstand performance for GIS spacer under residual DC voltage. Under the DC stress, the electrification of charges strengthen the electrical field strength at creepage surface (Et) and withstand performance for GIS spacer depends on the maximum value of Et (Etmax). When volume resistivities at surface layer of spacer are uneven, Et strengthen at the uneven spot. In this paper, Etmax under DC stress with uneven volume resistivities at surface layer of spacer is investigated, moreover, the evaluation test method for withstand performance under residual DC charge are constructed and proposed.

A Resonant Micromachined Electrostatic Charge Sensor

A micromachined electrometer, based on the concept of a variable capacitor, has been designed, modeled, fabricated, and tested. The device presented in this paper functions as a modulated variable capacitor, wherein a dc charge to be measured is up-modulated and converted to an ac voltage output, thus improving the signal-to-noise ratio. The device was fabricated in a commercial standard SOI micromachining process without the need for any additional processing steps. The electrometer was tested in both air and vacuum at room temperature. In air, it has a charge-to-voltage conversion gain of 2.06 nV/e, and a measured charge noise floor of 52.4 e/rtHz. To reduce the effects of input leakage current, an electrically isolated capacitor has been introduced between the variable capacitor and input to sensor electronics. Methods to improve the sensitivity and resolution are suggested while the long-term stability of these sensors is modeled and discussed.

Demonstrating the model nature of the high-temperature superconductorHgBa2CuO4+δ

The compound ${\text{HgBa}}_{2}{\text{CuO}}_{4+\ensuremath{\delta}}$ (Hg1201) exhibits a simple tetragonal crystal structure and the highest superconducting transition temperature $({T}_{c})$ among all single Cu-O layer cuprates, with ${T}_{c}=97\text{ }\text{K}$ (onset) at optimal doping. Due to a lack of sizable single crystals, experimental work on this very attractive system has been significantly limited. Thanks to a recent breakthrough in crystal growth, such crystals have now become available. Here we demonstrate that it is possible to identify suitable heat treatment conditions to systematically and uniformly tune the hole concentration of Hg1201 crystals over a wide range, from very underdoped (${T}_{c}=47\text{ }\text{K}$, hole concentration $p\ensuremath{\approx}0.08$) to overdoped $({T}_{c}=64\text{ }\text{K},\text{ }p\ensuremath{\approx}0.22)$. We then present quantitative magnetic susceptibility and dc charge transport results that reveal the very high-quality nature of the studied crystals. Using x-ray photoemission spectroscopy on cleaved samples, we furthermore demonstrate that it is possible to obtain large surfaces of good quality. These characterization measurements demonstrate that Hg1201 should be viewed as a model high-temperature superconductor.