High Current Levels Research Articles

High electrical performance liquid-phase HBr oxidation gate insulator of InAlAs/InGaAs metamorphic MOS-mHEMT

The InAlAs/InGaAs metal–oxide–semiconductor metamorphic high electron mobility transistors (MOS-mHEMTs) were demonstrated by using liquid-phase HBr treatment technology to form a high-quality gate insulator layer. In this study, liquid-phase HBr treatment technology was used instead of traditional plasma-assisted chemical vapor deposition (PECVD) because the proposed technology can prevent the device from plasma-induced damage. The novel HBr + ultraviolet (UV) illumination treated InGaAs provided a lower surface states such that MOS structure can be efficiently obtained. Besides, based on the atomic force microscopy (AFM) measurement, the native oxides film formed by HBr + UV illumination treatment also provided a better surface roughness compared to traditional NH 4OH and only HBr treatment solutions. It is beneficial for reducing the surface traps and lowering the leakage current in MOS-mHEMTs. Based on the flicker noise and load-pull power measurement results, HBr + UV treatment mHEMT achieved a low flicker noise at high current level and the power-added efficiency can be enhanced up to 9%. Therefore, the novel liquid phase method of HBr + UV illumination treatment exhibited a highly potential for low noise microwave power device applications.

Optical Properties of the Partially Strain Relaxed InGaN/GaN Light-Emitting Diodes Induced by p-Type GaN Surface Texturing

Partial strain relaxation from the light-emitting diode (LED) with surface-textured p-GaN was observed. The textured device possesses less efficiency droop and a higher current level at the efficiency maximum, as compared with the planar one. The results suggest that surface roughening affects not only the external light extraction but also the internal quantum efficiency. Furthermore, the photoluminescent (PL) measurement at low temperature reveals that the percentage increment of the optical power of the textured LED over that of the planar LED becomes lower. In addition to the effect of frozen nonradiative defect states, the PL difference is related to the strain-correlated quantum-confined Stark effect.

Plasma arc cutting technology: simulation and experiments

Transferred arc plasma torches are widely used in industrial processes for cutting of metallic materials because of their ability to cut a wide range of metals with very high productivity. The process is characterized by a transferred electric arc established between an electrode inside the torch (the cathode) and another electrode, the metallic workpiece to be cut (the anode). In order to obtain a high quality cut and a high productivity, the plasma jet must be as collimated as possible and must have the higher achievable power density. Plasma modelling and numerical simulation can be very useful tools for the designing and optimizing these devices, but research is still in the making for finding a link between simulation of the plasma arc and a consistent prevision of cut quality. Numerical modelling of the behaviour of different types of transferred arc dual gas plasma torches can give an insight on the physical reasons for the industrial success of various design and process solutions that have appeared over the last years. Diagnostics based on high speed imaging and Schlieren photography can play an important role for investigating piercing, dross generation, pilot arcing and anode attachment location. Also, the behaviour of hafnium cathodes at high current levels at the beginning of their service life can been experimentally investigated, with the final aim of understanding the phenomena that take place during those initial piercing and cutting phases and optimizing the initial shape of the surface of the emissive insert exposed to plasma atmosphere.

Improved organic rectifier using polymethyl-methacrylate-poly 4-vinylphenol double layer

Organic thin film transistors, owing to their low-costs fabrication process and potential to be devised on flexible substrate, can be used for varied applications such as radio frequency identification tags, flexible electronics, biosensors and integrated circuits. In this regard, the authors fabricated a pentacene organic rectifier consisting of a transistor diode and a bridge rectifier. The poly 4-vinylphenol (PVP)-based single layer, which is optimised for high current level, and polymethyl-methacrylate (PMMA)-PVP double-layer structure were compared with respect to their rectification efficiency. The electrical properties of the organic rectifier could be improved by use of the PMMA-PVP double layer as an insulator compared with a single layer of PVP. The device structure was further modified to include a diode and bridge rectifier. The rectification efficiency of the diode and bridge rectifier could be increased by 10%.

A new LVI assisted PSFB DC-DC converter

In this study, a new Phase Shifted Full Bridge (PSFB) Pulse Width Modulated (PWM) isolated dc-dc converter is proposed. In the proposed converter, resonant inductor is replaced with Linear Variable Inductor (LVI) that is controlled by output current. The soft switching operation range is increased and the dependency of ZVS operation on the load current is decreased. The required energy for ZVS operation at low current levels is obtained by means of the high value of the LVI. The value of LVI decreases approximately linearly with increasing current. At high current levels parasitic resonance and duty cycle loss are decreased. By selecting the range of the LVI properly, the necessity of the dead time control between gate drive signals of the IGBTs in the lagging leg is eliminated. A prototype of single phase IGBT-based inverter arc welding machine is implemented by using the proposed converter which operates at 75 kHz switching frequency and 5 kW output power. The experimental results taken from the converter show the feasibility of the proposed method.

Statin use after first myocardial infarction in UK men and women from 1997 to 2006: Who started and who continued treatment?

Background and aimsTo examine trends in initiation and continuation of statin treatment after myocardial infarction (MI) and their determinants, during a period of increasing usage. Methods and results9367 patients aged 30–84 with a first Myocardial Infarction (MI) in 1997–2006 were identified in DIN-LINK, an anonymised, UK primary care database. We assessed statin initiation (prescription within 6 months of MI) and continued therapy (% covered by a prescription on a given day of those prescribed a statin within 6 months). The influences of co-morbidities and socio-economic deprivation (Index of Multiple Deprivation) were examined.Statin initiation increased from 37% for MIs in 1997 to 92% in 2006. Continuation at 1 year remained stable over successive cohorts at approximately 80%, settling to about 76% in patients with 5–10 years follow up. Younger age, affluence, revascularisation in 6 months after MI, and absence of congestive heart failure, predicted higher initiation and continuation; a diagnosis of hypertension or diabetes predicted higher initiation, while smoking was associated with poorer continuation. Men had higher initiation and continued therapy, but these effects were largely explained by their younger age. Type of statin initially prescribed did not influence continued usage. ConclusionStatin use after MI increased markedly between 1997 and 2006, whilst continued therapy remained high and stable. Importantly, first choice of statin had no effect on continuation. Whilst the high current levels of initiation may have reached a ceiling, increasing continuation rates among smokers, older patients and those from lower socio-economic groups, should remain a priority.

Conversion between anticipating and lag chaos synchronization induced by different bias current levels in mutually delay-coupled semiconductor lasers

Based on a mutually delay-coupled semiconductor lasers (SLs) system, through adjusting the bias current of a SL and fixing that of the other one, the conversion between anticipating and lag chaos synchronization of this system has been experimentally observed for the first time. Experimental results show that for two SLs with the similar operation parameters, the SL biased at a relatively higher current level plays a leader role due to its relatively higher output power. Considering that the SL with a higher bias current level will oscillate at a longer wavelength, the SL with a longer wavelength becomes the leader, which provides a synchronization conversion scheme via by purely electronic current drive. Furthermore, the corresponding theoretical analyses have been given, and show that whether the SL with a longer or shorter wavelength becomes the leader mainly depends on the approach of the driving of frequency detuning between the two SLs.

Health inequalities affect the health of all

> ‘We must never forget: evidence has great strategic and persuasive power at the policy level.’ ( Director-General of the World Health Organization, 2007 ) The runaway publishing success of The Spirit Level by Wilkinson and Pickett has put health inequalities on everyone's lips.1,2 Using the evidence, based on decades of research, they remind us that the causes of most health inequalities in developed countries are rooted in the structure of society and particularly in income inequalities. Using data from 23 of the richest countries, and a separate analysis for the 50 states of North America, they illustrate the social gradient in life-expectancy, and physical health, along with other factors on the index of health and social problems, such as educational performance, levels of trust within local communities, imprisonment rates, teenage births, and homicides. Every country and North American state has a social gradient for each of these factors. But the book's message is that the level of income inequalities within developed countries will determine where a country falls on the international gradient. Hence the UK, with high current levels of income inequality, will fall low on the international gradient for many of the societal factors that predict premature mortality and chronic ill health. Combining this international message with that from the recent Marmot Review of health inequalities in England makes for serious reflection. Marmot confirms the continuing mortality gradient of 7 …

Experimental analysis of the behaviour of high current electrodes in plasma arc cutting during first cycles

The behaviour of hafnium (Hf) cathodes at the beginning of their service life when operating at high current levels (250 A) in the plasma arc cutting (PAC) process has been experimentally investigated with the final aim of describing the phenomena that take place during those initial cutting cycles (CCs), and optimizing (with respect to expected service life) the initial shape of the electrode emissive surface. The experimental tests were carried out under realistic operative conditions for cutting mild steel plates with oxygen/air as the plasma/shield gas. Starting with an electrode with a new planar emissive surface, subsequent CCs were completed. With each cycle the dimensions of the growing concave recess naturally created on the insert, and the amount of Hf oxide (HfO2) collected on the nozzle surface and on the flat surface around the edge of the recess was recorded. Morphological and compositional analysis of the tested electrodes and nozzles led to a detailed description of Hf erosion mechanisms, modifications of the Hf insert morphological structure, and effects of HfO2 deposits on the nozzle inner surface. High-speed imaging during early stages of the transferred arc mode has been used to highlight the possible presence of non-destructive double-arcing phenomena taking place during the first few CCs as a consequence of deposition of HfO2 on the nozzle. Conclusions can be drawn concerning the optimization of the dimensions of the initial recess of the Hf insert fit to avoid the massive deposition of material on the nozzle inner surface that would cause a strong reduction of electrode and nozzle service life and a rapid degrading of cut quality.

The effect of amorphous carbon layer on the field emission characteristics of carbon nanotube film

Carbon nanotube (CNT) has excellent field emission characteristics and could play as a good cold cathode in the application of vacuum electronic devices. However, the practical application faces a big obstacle regarding current fluctuation and deterioration of the CNT cathode. In this research, the formation of amorphous carbon (ac) layer between the CNT film and the substrate, and the effect of the existence of this layer on field emission stability of the CNT film are studied. The formation of the ac layer could be controlled by adjustment of growth temperature and hydrocarbon flow rate. The field emission character and current stability of the CNT film without ac layer are better than those of the CNT film with ac layer. The results attribute to the ac layer a thermal disequilibrium state under high current level. Moreover, adhesion capacity of the CNT film without ac layer is also better than that with the ac layer. It is concluded that the ac layer between the CNT film and substrate is a key factor in the stability of field emission characteristics and should be eliminated before applications.

Effects of electrical stimulation on the acoustically evoked auditory-nerve response in guinea pigs with a high-frequency hearing loss

Criteria for cochlear implantation keep expanding and people with substantial residual low-frequency hearing are considered candidates for implantation nowadays. Therefore, electro-acoustical stimulation in the same ear (EAS) is receiving increasing interest. We have investigated the effects of intracochlear electrical stimulation on acoustically evoked auditory-nerve activity, using a forward masking paradigm. The stimulation electrode was placed in the basal turn of the cochlea. Compound action potential (CAP) recordings were performed in guinea pigs with severe high-frequency hearing loss and in normal-hearing control animals. In normal-hearing animals, electrical stimulation generally suppressed CAPs, especially at high acoustic frequencies (8 and 16 kHz) and low sound levels. At low frequencies (0.5 and 1 kHz), suppression was observed only at high sound levels. In animals with a high-frequency hearing loss, suppression of CAPs at low frequencies was substantially less compared to control animals, even at high current levels and temporal overlap of acoustic and electric stimuli. Hence, effects of electrical stimulation substantially differed between normal-hearing animals and animals with a high-frequency hearing loss. These findings stress the need for a proper animal model when investigating EAS. We conclude that in case of high-frequency loss, the basal part of the cochlea can be stimulated electrically with little effect on responses to low-frequency acoustic stimuli.

Study on Time Constants of Random Telegraph Noise in Gate Leakage Current Through Hot-Carrier Stress Test

Capture and emission time constants obtained from random telegraph noise in gate leakage current ( Ig RTN) are studied by characterizing an intentionally created trap in thin gate oxide (2.6 nm) in metal-oxide-semiconductor field-effect transistors (MOSFETs). The single oxide trap was generated at the drain edge region in virgin nMOSFETs by drain-avalanche hot-carrier stress. By analyzing the location and energy level of the trap extracted from the experimental data, the time constants of high and low current levels in Ig RTN were found to be capture and emission times, respectively.

High current fast switching n-ZnO/p-Si diode

The authors report on the high current density n-ZnO/p-Si heterojunction diode that has been fabricated by atomic layer deposition (ALD) of 70 nm thin ZnO on a p-Si substrate. While the diode was formed at four different ALD temperatures of 80, 100, 150 and 200 °C, the 100 °C processed diode showed an optimal behaviour of an on–off ratio over 3.3 × 103 and a high forward current density, ∼300 A cm−2 at 3 V. Although the highest film conductance appeared from the 200 °C deposited ZnO layer, nanometre thin SiOx was also revealed at the ZnO/p-Si interface; it might cause a high reverse leakage current level. Our high current density diode also demonstrates a fast switching performance without any reverse recovery delay, which is often observed at a usual Si p–n diode.

InGaN staircase electron injector for reduction of electron overflow in InGaN light emitting diodes

Ballistic and quasiballistic electron transport across the active InGaN layer are shown to be responsible for electron overflow and electroluminescence efficiency droop at high current levels in InGaN light emitting diodes both experimentally and by first-order calculations. An InGaN staircase electron injector with step-like increased In composition, an “electron cooler,” is proposed for an enhanced thermalization of the injected hot electrons to reduce the overflow and mitigate the efficiency droop. The experimental data show that the staircase electron injector results in essentially the same electroluminescence performance for the diodes with and without an electron blocking layer, confirming substantial electron thermalization. On the other hand, if no InGaN staircase electron injector is employed, the diodes without the electron blocking layer have shown significantly lower (three to five times) electroluminescence intensity than the diodes with the blocking layer. These results demonstrate a feasible method for the elimination of electron overflow across the active region, and therefore, the efficiency droop in InGaN light emitting diodes.

Growth of Bulk GaN and AlN: Progress and Challenges

GaN-based optoelectronic and electronic devices such as light-emitting diodes (LEDs), laser, and heterojunction field-effect transistors (HFETs) typically use material grown on foreign substrates such as sapphire, Si, and SiC. However, thermal and lattice mismatch present prevent attainment of quality films deemed necessary by ever increasing demand on device performance. In fact in LEDs intended for solid state lighting, internal quantum efficiencies near 100% might be needed, and further these high efficiencies would have to be retained at very high injection current levels. On the electronic device side, high radio-frequency (RF) power, particularly high-power switching devices, push the material to its limits. Consequently, as has been the case for other successful semiconductor materials systems, native substrates must be developed for the GaN family. In this paper, various approaches such as high-pressure nitrogen solution (HPNS), ammonothermal, and Na flux methods, and an intermediary technique called the hydride vapor phase epitaxy (HVPE; to a lesser extent as there is a review devoted to this technique in this issue) along with their strengths and challenges are discussed.

Investigations on Surge Current Capability of SiC Schottky Diodes by Implementation of New Pad Metallizations

In this paper we describe how a merged pn Schottky diode (MPS diode) is capable to drive surge current levels far beyond the normal current of the diode and how to improve the device in order to achieve even higher surge current levels. For a sine half wave of 10 µs an 8A MPS diode (size: 2.52mm2) with conventional Al pad metallization shows surge current levels of greater than 500A, using Cu it can be increased to ~900A. For 10ms pulse length a different behaviour was observed, here diodes with Al pad metallization show a higher surge current level (80A) compared to Cu pad metallization (~ 40A). The root cause for this negative result at longer pulse time is based in a chemical interaction between Cu and the Schottky metal (Ti). Additionally, an outlook is given how Cu can contribute to improved surge current capability also at longer pulse lengths.

Electromigration in flip chip solder joints under extra high current density

Electromigration in flip chip solder joints under extra high current density (4.5×104 A/cm2) is studied. At such a high current density level, due to Joule heating, the chip temperature is strongly coupled to the applied current density. Accordingly, it is highly desirable to have the capability to decouple the chip temperature and the current density. Two experimental setups were used in this study, one with a cooling module to keep the chip temperature constant and the other one without a cooling module. Without the cooling module, the temperature increased rapidly with the applied current. When the current density reached 4.5×104 A/cm2, a rapid failure caused by excessive Joule heating was observed only after 10 min of current stressing. With the cooling module attached, the joint exhibited a much longer life (935 h) under 4.5×104 A/cm2. It was successfully demonstrated that the cooling module was able to decouple the applied current density and the chip temperature.

Components of Negative Affect As Moderators of the Relationship Between Early Drinking Onset and Binge-Drinking Behavior

This study examines the moderating effects of negative affect on the relationship between early drinking onset and binge-drinking behavior. Six hundred and thirty-five eleventh- and twelfth-grade students completed the American Drug and Alcohol Survey and reported on a variety of measures, including items assessing anxiety, anger, depression, age first drunk, and current level of binge drinking. Results indicate that males that began drinking at age 12 or younger and reported higher levels of anxiety and depression showed higher current levels of binge drinking compared to later onset drinking males. In addition, female early onset drinkers with higher levels of anger showed lower current levels of binge drinking compared to later onset drinking females. Results are discussed in regard to understanding and preventing binge-drinking behavior.

A Micromachined Robust Planar Triggered Sparkgap Switch for High Power Pulse Applications

High voltage (HV) switches capable of operating at high speeds with high current levels are used in a variety of applications in commercial and government systems. Examples of HV switches include triggered sparkgap, dielectric breakdown, and mercury vapor switches. The triggered sparkgap switch is a three-element, gas-filled, ceramic-to-metal, hermetically sealed, pressurized switch that operates in an arc discharge mode. Triggered sparkgaps have been in use for many years, providing precision timing and activation of in-flight functions such as missile stage separation. These applications involve the activation of electro-explosive devices such as an exploding bridge-wire [EBW] or an exploding foil initiator [EFI]. This paper discusses the fabrication and characterization of a novel high voltage planar discharge switch using micromachining techniques. The switch provides a low cost alternative to conventional triggered sparkgaps. The switch is designed for direct integration into the strip-line geometries used in a conventional capacitive discharge unit (CDU). The geometry of the device was selected to minimize parasitic impedances associated with conventional firing circuits. The switch design is microfabricated on an alumina substrate utilizing a patterned electron-beam deposited metallic stack. A polyimide layer selectively deposited over the metal stack provides dielectric isolation and passivation for the switch electrodes. A similar methodology was utilized to fabricate sample EFIs for switch validation tests with insensitive secondary high explosive (HE) pellets. The discharging of the HV capacitor through the patterened bridgefoil of an EFI results in rapid vaporization of the metal stack. The high pressure gas formed by the vaporized metal accelerates the adjacent polyimide layer to high velocity. The polyimde layer then impacts the HE pellet, inducing a shock wave, which results in prompt detonation of the material. Thus, this device is a type of MEMS actuator with a very specialized use. Design, fabrication and test data are presented and discussed.

Size-dependent light output, spectral shift, and self-heating of 400 nm InGaN light-emitting diodes

We have systematically investigated the impact of device size scaling on the light output, spectral shift, and self-heating of 400 nm InGaN light-emitting diodes (LEDs). Devices with diameters in the range 20–300 μm have been studied. It is shown that smaller LED pixels can deliver higher power densities (despite the lower absolute output powers) and sustain higher current densities. Investigations of the electroluminescence characteristics of differently sized pixels against current density reveal that the spectral shift is dominated by blueshift at the low current density level and then by redshift at the high current density level, owing to the competition between the bandgap shrinkage caused by self-heating and band-filling effects. The redshift of the emission wavelength with increasing current density is much faster and larger for the bigger pixels, suggesting that the self-heating effect is also size dependent. This is further confirmed by the junction-temperature rise measured by the established spectral shift method. It is shown that the junction-temperature rise in smaller pixels is slower, which in turn explains why the smaller redshift of the emission wavelength with current density is present in smaller pixels. The measured size-dependent junction temperature is in reasonable agreement with finite element method simulation results.