Internal Diodes Research Articles

A novel bidirectional DC–DC converter with high voltage conversion ratio and capability of cancelling input current ripple

AbstractThis paper proposes a novel bidirectional DC–DC converter with high voltage conversion ratio and capability of cancelling input current ripple. The proposed converter uses two coupled inductors and switched‐capacitor circuit to increase the voltage conversion ratio. The input current ripple at low voltage side can be eliminated for a pre‐selected duty cycle by adjusting special values of magnetizing inductances of coupled inductors. The input current is divided into two paths of the primary winding of coupled inductors that causes the decrease in the current stresses of switches. The proposed converter has five switches that consist the internal diodes of switches to bring about bidirectional power flow and have boost and buck operations. Here, the proposed topology is analysed in all operating modes and the current and voltage stresses of switches, input current ripple cancelling condition and voltage conversion ratio are calculated. Finally, the accuracy performance of the proposed converter is reconfirmed through EMTDC/PSCAD simulation and experimental results for boost operations.

Predicting the performance of portrait-aligned vertical bifacial agrivoltaic arrays

This work simulated and contrasted the expected electrical output of portrait-oriented vertical bifacial (VBF) solar modules versus the more frequently installed landscape-oriented modules, designed and spaced apart suitably for an agrivoltaic installation. In the portrait orientation, the expected early morning and late afternoon inter-row shading is not protected by the module’s internal bypass diodes. Instead, the top and bottom halves of portrait-oriented modules operate at independent currents, leading to a different power output than a landscape-oriented module in the same circumstance. The effects of the module dimensions, module height, row spacing, and bifaciality are all taken into account. The overall annual output for the portrait orientation was comparable to that of the landscape orientation, though differences exist and the portrait modules exceeded the output of the landscape modules in specific situations. This suggests that a variety of racking options can be considered when designing VBF arrays. For an array with rows of portrait-oriented modules with bifaciality of 92 %, an energy output of over 157 MWh/acre/year (388 MWh/hectare/year) is expected with a row spacing of 20 feet (6.1 m).

A Comparative Evaluation of Wide-Bandgap Semiconductors for High-Performance Domestic Induction Heating

This paper presents a comparative evaluation of wide-bandgap power semiconductor devices for domestic induction heating application, which is currently a serious alternative to traditional heating techniques. In the induction heating system, the power transferred to the output depends on the equivalent resistance of the load, and the resistance depends on the operating frequency. Due to the switching characteristics of wide-bandgap power semiconductor devices, an induction heating system can be operated at higher operating frequencies. In this study, SiC and Si semiconductor devices are used in the comparison. These devices are compared according to different evaluation issues such as the turn-off energy losses, turn-off times, current fall time, the power losses of the internal diodes, and the conduction voltage drops issues. To perform the proposed evaluation, the series-resonant half-bridge inverter, which is frequently used in state-of-the-art induction heating systems, has been selected. The device suitability in an induction heating system is analyzed with the help of a test circuit. A comparison is made in terms of criteria determined by using the selected switches in the experimental circuit, which is operated in the 200 W to 1800 W power range and 45 kHz to 125 kHz switching frequency range. System efficiency is measured as 97.3% when Si IGBT is used. In the case of using SiC cascode JFET, the efficiency of the system is increased up to 99%.

Correcting Calibration Drifts Using Solar and Lunar Intrusions for Miniaturized Microwave Radiometers

CubeSats with miniaturized microwave radiometers are now demonstrating the potential to provide science-quality weather measurements. For example, the Micro-Sized Microwave Atmospheric Satellite-2A (MicroMAS-2A) and Temporal Experiment for Storms and Tropical Systems–Demonstration (TEMPEST-D) CubeSats are both launched in 2018 and have demonstrated microwave atmospheric sounder data from orbit. The NASA Time-Resolved Observations of Precipitation structure and storm Intensity with a Constellation of Smallsats (TROPICS) mission is a follow-on constellation of six 3U CubeSats based on the MicroMAS-2 design that is scheduled for launch no sooner than 2021. The TROPICS sensors use internal noise diodes (NDs) for calibration. Although the NDs on TROPICS are similar to technology flown on GMI, they have not been tested on-orbit at TROPICS frequencies. In order to track and correct ND drift, we develop a novel method of calibration for CubeSat constellations, such as TROPICS, by incorporating periodic solar and lunar intrusions as an additional source of information to counter ND drift. These lunar intrusions also occur for existing satellites hosting microwave radiometers in sun-synchronous polar orbits but are much more infrequent than for the TROPICS constellation’s scanning payload. In this work, we develop a solar/lunar calibration correction algorithm and test it using advanced technology microwave sounder (ATMS) lunar intrusion data. The mean bias and standard deviation between the solar/lunar calibration correction algorithm and actual ATMS data fall within the expected ATMS error budget of 0.6–3.9 K, validating our model.

Maximizing fucoxanthin production in Odontella aurita by optimizing the ratio of red and blue light-emitting diodes in an auto-controlled internally illuminated photobioreactor

Fucoxanthin has multiple beneficial effects on human health. However, an efficient cultivation strategy for hyper-production of microalgae-based fucoxanthin has been seldom achieved. Here, an auto-controlled photobioreactor (PBR) installed internal light-emitting diodes illumination with adjustable spectra ratio was firstly used to culture Odontella aurita. The results showed that red light (RL) was more suitable for cell growth and fucoxanthin accumulation than blue light (BL) and white light. The biomass and fucoxanthin production were further promoted by optimizing the ratios of RL and BL, with 8:2 giving the highest productivities of 570 and 9.41 mg L-1 d-1, respectively, which is the highest fucoxanthin productivity ever reported under photoautotrophic cultivation. Pilot-scale cultivation demonstrated its promising feasibility in commercial fucoxanthin production. Our study represents a pioneering work of harnessing the PBR with internal illumination for hyper-production of microalgae-based fucoxanthin, and provides feasible strategies for high-efficient production of other value-added products in related species/strains.

Enhanced Non-Uniformity Modeling of 4H-SiC Schottky Diode Characteristics Over Wide High Temperature and Forward Bias Ranges

A practical model, adequate for full reproduction of inhomogeneous Schottky diodes' forward characteristics over wide high-temperature and bias ranges, is proposed. According to this p-diode model, the Schottky contact current is considered to flow through m parallel-connected internal diodes, each with stable, constant barrier height and specific series resistance (both main model parameters). The value of m, required to reproduce the entire electrical forward behavior of a non-uniform Schottky contact, is directly connected to a particular model parameter (p <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eff</sub> ), used to define the inhomogeneity degree. The p-diode model was tested on forward characteristics measured for both Ni and commercial Ti Schottky diodes on 4H-SiC, which exhibited varying degrees of inhomogeneity. Excellent replication of experimental curves was achieved for all investigated samples, even those with obvious irregularities, such as “humps”, explained in the model by the series resistances' influence. In the case of m = 1, the proposed model does not produce identical results with the conventional model of a homogeneous Schottky contact if p <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eff</sub> ≠ 0. The value of this parameter indicates how much of an inhomogeneous contact's area is essentially used for current conduction.

A review on the design and development of photocatalyst synthesis and application in microfluidic reactors: challenges and opportunities

AbstractMicrofluidics is an emerging branch of science that has significant applications in various fields. In this review paper, after a brief introduction to the concept of photocatalysis, nanoparticle preparation methods and film formation techniques have been studied. Nanoparticle synthesis in microfluidic systems and microreactor types for on-chip photocatalyst synthesis and challenges of nanoparticles handling in microsystems have been reviewed. To resolve particle polydispersity and microchannel clogging, a good suggestion can be the use of droplet-based microreactors. The configurative designs for the microfluidic reactor with immobilized photocatalysts, their applications, and their challenges have been comprehensively addressed. The three main challenges ahead the immobilized photocatalytic microfluidic reactors are optimal light distribution, prevention of the recombination of photogenerated electrons and holes, and improved mass transfer. Internal light-emitting diodes with a waveguide can resolve the number one challenge of photocatalysis application in optofluidic reactors, that is, light distribution.

Shutter Technique for Noninvasive Individual Cell Characterization in Sealed CPV Modules

An optical shutter technique for quality control and degradation analysis of concentrating photovoltaic (CPV) modules is presented. Shuttering configurations are described and used to determine individual component degradation or failure in field-exposed commercial modules. Cells are shuttered in specific patterns, intentionally engaging internal bypass diodes, and current–voltage ( I – V ) curves are measured at the housing terminals of the sealed module. Individual cell characteristics may be qualitatively determined by contrasting module I – V responses to different shutter configurations and quantitatively determined by fitting an extended equivalent circuit model to the shutter data.

Current and illumination dependent series resistance of solar cells

Precise knowledge of the series resistance is essential for failure and loss analysis as well as yield prediction of solar cell devices. In this work, a method which determines the current and photogeneration dependence of the series resistance without assuming any specific current-voltage characteristic for the internal diodes is presented. This approach is of particular interest for solar cells which cannot be described by the one- or two-diode model such as organic solar cells. Furthermore, it clarifies the difference in the series resistance values that are obtained from current-voltage curves in the dark and under illumination as well as short-circuit-current and open-circuit-voltage characteristics. Additionally, it is shown how other cell parameters, such as the shunt resistance or the current-voltage characteristic of the internal diode are determined in a consistent way. Finally, it is demonstrated that our approach can be easily implemented in a new generation of solar simulators that are based on light-emitting diodes instead of conventional light sources.

SU-E-T-144: Daily and Monthly Quality Assurance with TomoDose.

Examine the use of TomoDose for Tomotherapy quality assurance. Baseline TomoDose profiles are acquired annually in accordance with TG-148. During monthly quality assurance, TomoDose is irradiated with a static beam and referenced to baseline. Differences between superimposed profiles are evaluated monthly. TomoDose is further utilized in verifying transverse laser alignment. The TomoDose is aligned to virtual isocenter lasers and statically irradiated with a 40cm × 5.02cm treatment beam. Next, the TomoDose's internal diodes are imaged using the MVCT. Transverse laser, imaging beam, and treatment beam field center are verified to less than 1mm coincidence difference. For daily TomoDose irradiation the couch is set to a fixed height and irradiated. The dose to the central axis and dose rate is recorded. To check energy, the measurement is repeated with an aluminum block placed centrally on the TomoDose. The output reading relative to the dose rate is compared to the baseline determined at the time of monthly verification. A ratio of the output and energy readings serves as a daily energy constancy check. Over 28 months, for nominal field sizes of 1.05, 2.50, and 5.02cm, TomoDose measured an average field size of 1.10, 2.51, and 5.02cm with maximum deviations of 0.09, 0.09, and 0.10cm, respectively. For transverse laser alignment, TomoDose software calculates beam center location. We have found the alignment to be sensitive to sub-millimeter changes. Our nominal daily energy ratio is 0.689. We have observed a decline from an estimated 0.693 to 0.680 with target wear, providing a good indicator of degradation. TomoDose serves as a reliable constancy device with added benefits of verifying transverse laser alignment and predicting target health. I own common stock in Accuray (Tomotherapy).

Approaches for high internal quantum efficiency green InGaN light-emitting diodes with large overlap quantum wells

Optimization of internal quantum efficiency (IQE) for InGaN quantum wells (QWs) light-emitting diodes (LEDs) is investigated. Staggered InGaN QWs with large electron-hole wavefunction overlap and improved radiative recombination rate are investigated for nitride LEDs application. The effect of interface abruptness in staggered InGaN QWs on radiative recombination rate is studied. Studies show that the less interface abruptness between the InGaN sub-layers will not affect the performance of the staggered InGaN QWs detrimentally. The growths of linearly-shaped staggered InGaN QWs by employing graded growth temperature grading are presented. The effect of current injection efficiency on IQE of InGaN QWs LEDs and other approaches to reduce dislocation in InGaN QWs LEDs are also discussed. The optimization of both radiative efficiency and current injection efficiency in InGaN QWs LEDs are required for achieving high IQE devices emitting in the green spectral regime and longer.

Investigation of the Carrier Dynamic in GaN-Based Cascade Green Light-Emitting Diodes Using the Very Fast Electrical–Optical Pump–Probe Technique

For the first time, the internal carrier dynamic inside GaN-based green light-emitting diodes (LEDs) during operation has been directly observed using the demonstrated electrical-optical pump-probe technique. Short electrical pulses (~100 ps) were pumped into high-speed cascade green LEDs, and the output optical pulses were probed using high-speed photoreceiver circuits. Using such a method, the recombination time constant of the carriers can be directly measured without any assumption about the recombination process. A high-speed cascade LED structure was adopted in the experiments to eliminate the influence of the RC delay time on the measured responses. Our measurement results indicate that both single- and three-LED cascade structures have the same internal response time due to current continuity. Furthermore, based on responses measured under different temperatures (from 25°C to 200°C), the origin of the efficiency droop in GaN-based green LEDs under a high bias current density may be attributed to the strong nonradiative Auger effect rather than device heating or carrier overflow. The demonstrated measurement scheme and high-speed cascade device structure offer a novel and simple way to straightforwardly investigate the internal carrier dynamic inside the active layers of the LED during forward-bias operation.

Improved Reliability and ESD Characteristics of Flip-Chip GaN-Based LEDs With Internal Inverse-Parallel Protection Diodes

In this letter, a GaN/sapphire light-emitting diode (LED) structure was designed with improved electrostatic discharge (ESD) performance through the use of a shunt GaN ESD diode connected in inverse-parallel to the GaN LED. Thus, electrostatic charge can be discharged from the GaN LED through the shunt diode. We found that the ESD withstanding capability of GaN/sapphire LEDs incorporating this ESD-protection feature could be increased from several hundreds up to 3500 V in the human body model. Furthermore, flip-chip (FC) technology was also used to produce ESD-protected LEDs to further improve light output power and reliability. At a 20-mA current injection, the output power of the FC LEDs showed an improvement of around 60%. After a 1200-h aging test, the luminous intensities of the FC LEDs featuring an internal ESD-protection diode decreased by 4%. This decay percentage was far less than those of non-FC LEDs

On the Long-Term Stability of Microwave Radiometers Using Noise Diodes for Calibration

Results are presented from the long-term monitoring and calibration of the National Aeronautics and Space Administration Jason Microwave Radiometer (JMR) on the Jason-1 ocean altimetry satellite and the ground-based Advanced Water Vapor Radiometers (AWVRs) developed for the Cassini Gravity Wave Experiment. Both radiometers retrieve the wet tropospheric path delay (PD) of the atmosphere and use internal noise diodes (NDs) for gain calibration. The JMR is the first radiometer to be flown in space that uses NDs for calibration. External calibration techniques are used to derive a time series of ND brightness for both instruments that is greater than four years. For the JMR, an optimal estimator is used to find the set of calibration coefficients that minimize the root-mean-square difference between the JMR brightness temperatures and the on-Earth hot and cold references. For the AWVR, continuous tip curves are used to derive the ND brightness. For the JMR and AWVR, both of which contain three redundant NDs per channel, it was observed that some NDs were very stable, whereas others experienced jumps and drifts in their effective brightness. Over the four-year time period, the ND stability ranged from 0.2% to 3% among the diodes for both instruments. The presented recalibration methodology demonstrates that long-term calibration stability can be achieved with frequent recalibration of the diodes using external calibration techniques. The JMR PD drift compared to ground truth over the four years since the launch was reduced from 3.9 to -0.01 mm/year with the recalibrated ND time series. The JMR brightness temperature calibration stability is estimated to be 0.25 K over ten days.

Highly Reliable Nitride-Based LEDs With Internal ESD Protection Diodes

Nitride-based light-emitting diodes (LEDs) with internal electrostatic-discharge (ESD) protection diodes emitting at 460 nm were proposed and realized. By building an internal GaN p-n junction diode, a negative ESD-induced pulse current is expected to flow through the protection diode without damaging the major LED. The ESD characteristic of the fabricated LEDs was obviously improved with this design. Furthermore, the dimension of the internal p-n diode would influence the capacity for tolerating the ESD stress. It was found that a negative ESD threshold could be significantly increased from 300-400 to 2000 V. On the other hand, the authors managed to bring down the 20-mA operation voltage to 3.29 V using the n-metal finger, which entails a good current spreading under operation as the result of a reduced current-crowding effect. Since a good current spreading beneficially alleviates the thermal effect under long-term operation, an effective pattern layout design clearly would also prolong the lifetime of the proposed LEDs

LVTSCR structures for latch-up free ESD protection of BiCMOS RF circuits

The results of a numerical and experimental study aimed at increasing the holding on-state voltage of a low-voltage triggered silicon controlled rectifier are presented. Using TCAD numerical simulations two solutions are presented that are based on emitter injection control by the modification of the emitter–drain area ratio and by the addition of internal diodes in the emitter line. Experimental data generated in a 0.18 μm CMOS technology demonstrate the effectiveness of the new low-voltage triggered silicon controlled rectifier (LVTSCR) structures and validates the simulation results. It has been demonstrated that for the LVTSCR structures with high holding voltage the electrostatic discharge efficiency is 3–5 times higher than that of a conventional grounded gate snapback NMOS and simultaneously has 50% lower RF load capacitance.

High-resistivity GaAs grown by high-temperature molecular-beam epitaxy

It is shown that when grown by molecular-beam epitaxy at high temperatures around 700 °C, undoped GaAs layers display high resistivity. Preliminary results seem to imply that Ga-related inclusions that produce internal Schottky diodes might be responsible for this effect rather than the presence of deep centers. It is proposed that Ga-related inclusions that produce internal Schottky diodes might possibly be responsible for this effect rather than the presence of deep centers.

Optimization of the tradeoff between switching speed of the internal diode and on-resistance in gold- and platinum-implanted power metal-oxide-semiconductor devices

Diffusion of platinum and gold has been used to reduce minority-carrier lifetime in power metal-oxide-semiconductor devices in order to improve the switching characteristics of the internal diode. Gold thin-film deposition and gold- or platinum-ion implantation techniques have been adopted to realize the prediffusion source. For a given reduction in lifetime, the concomitant increase in the on-resistance of the device, as determined by the forward characteristics, is smaller in gold-implanted than in gold-deposited devices; an even smaller increase in on-resistance is obtained by using platinum implantation. Therefore, ion implantation of platinum in power MOS devices fabrication provides a better tradeoff between static characteristics of the devices and switching speed of their internal diodes. >

Noise studies in internal field emission diodes

The breakdown process of a zener diode in reverse direction is governed by internal field emission at low voltage and by impact ionization at higher voltage. For breakdown voltage in the transition range between 3 and 6 V, both physical processes appear in combination. Measuring the I– V characteristic and the noise current fluctuations spectral density it is possible to show the zener current multiplication by the multiplication effect described by Tager. In addition the I– V characteristic can be written empirically I = αV n .