Temperature Dependence Of Voltage Research Articles

Temperature dependence of superstructure and electrical tree initiation voltage of polyethylene

Below the melting point, polyethylene forms a structure in which the crystalline and the amorphous regions exist together. Therefore, polyethylene is not homogeneous. It is thought that generation of a crack by Maxwell stress is one of the tree initiation causes. The crack is generated easier in an unhomogeneous than in a homogeneous structure. Above the melting point, the homogeneity may increase because all crystalline regions melt into the amorphous region. To examine the homogeneity of polyethylene and the relationship to the generation of electrical trees, polyethylene was heated up to 180 °C. The relationship between the superstructure and the electrical tree initiation voltage at various temperatures was examined. © 1999 Scripta Technica, Electr Eng Jpn, 128(3): 24–30, 1999

A new generation of fast-switching thyristors

A new generation of fast-switching thyristors (FSThs) has been developed. It includes 100–1000 A/800–1200 V and 160–2000 A/2000–2500 V devices, turn-off times of them are equal to 6.3–12.5 μs and 32–63 μs, respectively. A new cathode emitter topology is proposed. It allows one to exclude the influence of the passive area of a p–n–p–n structure on the temperature dependence of maximal off-state voltage V Dm, on the values of critical rate of rise of off-state voltage (d V D/d t) cr and on the turn-off time t q. It also promotes some reduction of turn-on losses. Prototype samples of 1600–2000 A, 2500 V FSTh, having such cathode emitter topology, were fabricated. Their testing results confirm a new approach for the design of FSTh cathode emitter topology.

Investigation of acoustoelectric phenomena in Sn2P2S6 single crystals

The ultrasonic measurements of electronic attenuation have been performed in the crystals of ferroelectric semiconductor Sn2P2S6, which exhibit strong piezoelectric effect. From the dependence of electronic attenuation of ultrasound on conductivity the electromechanical coupling parameters have been calculated. The temperature dependence of acoustoelectric voltage has been measured and it was shown that it mainly follows the variation of electromechanical coupling constant. The influence of the long time crystal exposure in paraelectric phase near the phase transition temperature together with illumination of the Sn2P2S6 sample on ultrasonic velocity and attenuation has been also studied. It was shown, that relaxation of electronic subsystem significantly changes the critical ultrasonic behaviour. In this case the temperature anomalies of ultrasonic velocity and attenuation become very similar to that of feroelectric with incommensurate phase.

650-nm lasers with narrow far-field divergence with integrated optical mode expansion layers

By means of numerical simulation of the optical and electrical performance, we have designed 650-nm GaInP-AlGaInP quantum-well lasers with mode expansion layers which have a narrow vertical far-field divergence without sacrificing threshold current or threshold current temperature dependence. We have reduced the measured vertical far-field divergence in a 650-nm laser structure from 35/spl deg/ to 24/spl deg/ full-width at half-maximum without changing the threshold current, operating voltage, or threshold current temperature dependence. We have also calculated the tolerances in the thickness and composition necessary to realize this design in practice.

A Study on Hysteresis Effect of Barium Strontium Titanate Thin Films for Alternative Gate Dielectric Application

AbstractHysteresis effect of barium strontium titanate (BST) thin films for gate dielectric application has been studied. It is found that the “counterclockwise” hysteresis has strong sweep voltage and operating temperature dependence. It can be reduced or eliminated by proper thermal annealing or by using a barrier layer. A charge trapping and detrapping mechanism has been proposed.

Differential conductance of the ferromagnet/superconductor interface of DyBa2Cu3O7/La2/3Ba1/3MnO3 heterostructures

The voltage bias, temperature, and magnetic field dependence of the differential conductance of the interface between a half-metallic ferromagnet and a high-Tc superconductor have been studied in DyBa2Cu3O7/La2/3Ba1/3MnO3 heterostructures. Below the superconducting transition the differential conductance exhibits a dip at zero bias whose amplitude is a decreasing function of temperature and/or magnetic field. These results are interpreted qualitatively using a picture based on the suppression of Andreev reflection as a consequence of the high spin polarization of the carriers in the half-metallic ferromagnet.

Silicon MIS structures using samarium oxide films

MIS structures Al–Sm 2O 3–Si were formed by vacuum evaporation of the rare earth element on silicon wafer and by thermal oxidation of the rare earth metal layer in the air at a temperature of 500–550°C. The current–voltage characteristics and temperature dependence of current were measured using direct current. The surface with silicon was determined using the method of high-frequency capacitance–voltage characteristics. The barrier energies on the interfaces Al–Sm 2O 3 (2.88–2.92 eV) Ni–Sm 2O 3 (3.28–3.32 eV), Si–Sm 2O 3 (2.69–2.72 eV) were evaluated from the spectral characteristics of photocurrent by the threshold to internal electron emission and from the dependence of photocurrent on the bias applied to the structure. The main characteristics of photo-injection current and charge trapping in MIS structures with samarium oxide film are described.

Role of defects in producing negative temperature dependence of breakdown voltage in SiC

Electron beam induced current (EBIC) techniques were employed in order to understand the role of defects on the breakdown characteristics of SiC. EBIC images revealed that certain defects caused enhanced multiplication leading to the catastrophic failures in SiC diodes. The impact ionization coefficients for holes measured at the defective site (αp,eff) were found to be higher than those measured at a nondefective site. Also, αp,eff measured at the defective site was found to increase with increasing temperature in contrast with a defect free diode where αp decreases with increasing temperature, clearly indicating that the defects produce the observed negative temperature coefficient of breakdown voltage in SiC.

Characterization of highly doped n- and p-type 6H-SiC piezoresistors

Highly doped (/spl sim/2/spl times/10/sup 19/ cm/sup -3/) n- and p-type 6H-SiC strain sensing mesa resistors configured in Wheatstone bridge integrated beam transducers were investigated to characterize the piezoresistive and electrical properties. Longitudinal and transverse gauge factors, temperature dependence of resistance, gauge factor (GF), and bridge output voltage were evaluated. For the n-type net doping level of 2/spl times/10/sup 19/ cm/sup -3/ the bridge gauge factor was found to be 15 at room temperature and 8 at 250/spl deg/C. For this doping level, a TCR of -0.24%//spl deg/C and -0.74%//spl deg/C at 100/spl deg/C was obtained for the n- and p-type, respectively. At 250/spl deg/C, the TCR was -0.14%//spl deg/C and -0.34%//spl deg/C, respectively. In both types, for the given doping level, impurity scattering is implied to be the dominant scattering mechanism. The results from this investigation further strengthen the viability of 6H-SiC as a piezoresistive pressure sensor for high-temperature applications.

Thermally-stimulated spontaneous currents from metal-iodine doped polyvinyl pyrrolidone-metal system

A study of the spontaneous response currents from the metal-iodine doped polyvinyl pyrrolidone-metal (MPM) systems, on thermal stimulation at a constant rate, has been made with similar (Al-Al, Ag-Ag and Au-Au) and dissimilar (Al-Cu/Ag/Ni/PbZn) electrode systems. Thermograms of spontaneous current emission of iodine-doped PVP films exhibit two maxima around 90 ± 10°C and 130–160°C in the first heating run, whereas with the second heating run a single peak is found around 140–170°C. The magnitude and direction of current depend on the choice and combination of electrode materials. The position of the current peak in the thermal spectrum shifts with different heating run. A temperature dependence of open-circuit voltage (OCV) is also reported and it was found that OCV varied linearly with the difference in electrode work functions. The active centres of PVP are the carbonyl group of double-bond tertiary nitrogen atom (> N-C=O), and thus the charge transfer complexes are formed with iodine in PVP. The spontaneously-generated current is discussed in terms of weak complex formation with the water molecules and the liberation of different types of charges.

Neutral base recombination and its influence on the temperature dependence of Early voltage and current gain-Early voltage product in UHV/CVD SiGe heterojunction bipolar transistors

We present the first comprehensive investigation of neutral base recombination (NBR) in ultra-high vacuum/chemical vapor deposited (UHV/CVD) SiGe heterojunction bipolar transistors (HBT's), and its influence on the temperature characteristics of Early voltage (V/sub A/) and current gain-Early voltage product (/spl beta/V/sub A/). We show that a direct consequence of NBR in SiGe HBT's is the degradation of V/sub A/ when transistors are operated with constant-current input (forced-I/sub B/) as opposed to a constant-voltage input (forced-V/sub BE/). In addition, experimental and theoretical evidence indicates that with cooling, V/sub A/ in SiGe HBT's degrades faster than in Si bipolar junction transistors (BJT's) for forced-I/sub B/ mode of operation. Under the forced-V/sub BE/ mode of operation, however, SiGe HBT's exhibit a thermally-activated behavior for both V/sub A/ and /spl beta/V/sub A/, in agreement with the first-order theory. The differences in V/sub A/ as a function of the input bias and temperature for SiGe HBT's are accurately modeled using a modified version of SPICE. The performance of various practical SiGe HBT circuits as a function of temperature, in the presence of NBR, is analyzed using this calibrated SPICE model.

Breakdown characteristics in InP/InGaAs avalanche photodiode with p-i-n multiplication layer structure

We report on the breakdown voltages in InP/InGaAs avalanche photodiode (APD) experimentally and theoretically, based on the parameters of electric field distribution, carrier concentrations, thicknesses, and temperatures. According to the calculation, the breakdown voltage has its minimum point, w0, at each carrier concentration in charge plate and avalanche photodiode with very thin multiplication layer width will provide high gain bandwidth product. The devices having different multiplication layer width showed different breakdown voltages and temperature behaviors. We introduced newly defined temperature coefficient, γ, and found that γ’s are linearly dependent on breakdown voltages at each temperature. From these results, the empirical formula which effectively describes the temperature dependence of breakdown voltages was obtained.

Pulsed thermal characterization of a reverse biased pn-junction for ESD HBM simulation

Compact electro-thermal simulation of an ESD event in a semiconductor structure requires proper definition and calibration of the equivalent thermal circuit. We demonstrate an approach to determine the device temperature during square pulse stress on the basis of the temperature dependence of the avalanche breakdown voltage. This global temperature is relevant to the transient IV-characteristic. The simulation accuracy of an HBM-stressed diode is improved significantly.

High-breakdown voltage Al 0.66 In 0.34 As 0.85 Sb 0.15 /In 0.75 Ga 0.25 As/InPheterostructure field-effect transistors

Al0.66In0.34As0.85Sb0.15/In0.75Ga0.25As/InP heterostructure field-effect transistors (HFETs) with high breakdown voltage have been successfully fabricated by low-pressure metal organic chemical vapour deposition (LP-MOCVD). By virtue of an Al0.66In0.34As0.85Sb0.15 Schottky layer and an inverted δ-doped carrier supplier, a gate-to-drain breakdown voltage as high as 40 V can be obtained. Moreover, the temperature dependence of breakdown voltage shows a negative temperature coefficient.

A Simple Method for Determining the Temperature Coefficient of Voltaic Cell Voltage

Although use of the Nernst equation to illustrate the dependence of cell potential on half-cell concentrations is routinely covered in first-year college chemistry and high school AP chemistry classes, the temperature dependence of cell voltages is rarely encountered outside of the undergraduate physical chemistry laboratory. Even there, its coverage is somewhat limited because of the cost and sophistication of the instrumentation required. This article describes a relatively simple method for preparing voltaic cells, and through their temperature coefficient, _Eo/_T, it explores relationships between DeltaGo, DeltaHo and DeltaSo for the cell reactions involved.

An overvoltage self-protected thyristor with a structure to predict breakover voltage

A new concept for an overvoltage self-protected thyristor was theoretically analyzed and the thyristor manufactured. Its breakover operation is basically a combination of punchthrough and avalanche phenomena. Temperature dependence of the original structure in this thyristor is 5% from 20 to 125/spl deg/C. A second device which has a function to predict breakover voltage was also produced. The difference in temperature dependence of breakover voltage for both devices was investigated by an analytical model. Structures offering improved characteristics were proposed. The breakover voltage decrease of the developed structures at high temperature could be made equal to that of the original structure by a slight modification of the breakover region.

Temperature Dependence of Threshold Voltage of Metal-Semiconductor Field Effect Transistors in the Presence of an Uneven Distribution of Interface and Bulk States

The temperature dependence of threshold voltage of metal-semiconductor field effect transistors is studied considering a generalised interface state model and an uneven distribution of interface and bulk impurity states. The analysis predicts a sharp variation of threshold voltage with temperature which is in contrast to the conventionally known temperature dependence due to the band gap energy. The theoretical results are found in agreement with previous experimental findings.

Crossover of Noise Power from Thermal to Shot Noise in Superconducting Mesoscopic Devices

Low-frequency noise properties of all-thin-film superconducting Nb-(constrictions)-NbN point contacts have been investigated. This type of contact can be regarded as a superconducting mesoscopic system, and its quasiparticle characteristic can be analyzed effectively Blonder, Tinkham and Klapwijk ( BTK) theory based on the Bogoliubov-de Gennes equation. We also discuss on white noise in Nb-(constrictions)-NbN point contacts, in the clean and ballistic limit. The temperature dependence of crossover voltages between thermal noise and shot noise in the ballistic system is in good agreement with calculated values.

Current-temperature feedback effects in III-V heterojunction bipolar transistors

The consequence of the reciprocal relation between the temperature and current distributions in heterojunction bipolar transistors (HBTs) has been determined. The dc current voltage (I-V) characteristics, RF small-signal parameters, and temperature distributions of discrete devices with emitter fingers of varying lengths were analyzed empirically and their thermal profiles calculated numerically. The lateral temperature gradient induced in the finger due to power dissipation under normal operating conditions is shown to directly affect the current distribution in the transistor. The negative temperature dependence of the HBT base-emitter junction turn-on voltage results in positive feedback between current and temperature. This current temperature relationship leads to higher localized current densities in the hottest portion of the device, the center of the emitter. The temperature of the hot section rises with increasing power dissipation, continually drawing more current. Ultimately, the current through HBTs is localized to a comparable area at the finger center, independent of the emitter length.

PHOTOVOLTAIC WATER PUMPS COUPLED WITH DC/AC INVERTER

Proper sizing of photovoltaic (PV) array and motor/pump subsystem are essential for maximum utilisation of PV water pumping systems. A proper matching of electromechanical loads to a PV array is a great problem in many PV systems. This is mainly related to the non-linear, solar irradiance and cell temperature-dependent voltage and current characteristics of the PV array generator. In a proper matching system, the electrical energy supplied to the load is close to the maximum available array energy. The load matching factor is one of the basic comparison method used in the optimisation of PV water pumping systems. Optimisation of PV pumping system can be made from a simple non-linear mathematical model and from experimental data. From this optimisation technique, array configuration can be determined using the required rated power of the motor/pump subsystem and the I-V characteristic of a single cell. Conversely, the optimal size of motor/pump subsystem can be determined from a known array configuration. In this study, October field experiment data was taken to calculate the load matching factor of the PV system using K36 type Kyocera Solar modules (8 in series by 4 in parallel) and Grundfos made M402/SP5A-7 motor/pump with SA1500 dc/ac inverter interfacing device. The field test result shows that an optimum load matching factor of 0.72 can be achieved in October for this type of PV system in this works field study area. It is possible to achieve a higher load matching factor by carefully selecting the proper size of the array and the motor/pump subsystem. The load matching factor is used to prove the design quality of the PV system. The result shows that the load matching factor mainly depends on the solar radiation seasonal variations, and the array and the load characteristics.