Diode Forward Voltage Research Articles

A failure mechanism of IGBT module in MMC and improvement

In modular multi-level converter valves, as the blocked mode happens, the failure in IGBT modules often causes a chain explosion reaction, which masks the initial failure mechanism. The root cause of the failure was that the voltage, consisting of the diode forward voltage and the induced voltage on the parasitic inductance, exceeded the reverse blocking capability of the anti-parallel IGBT. The methods against the failure were studied from three aspects: decreasing the diode’s peak forward voltage, increasing the reverse blocking capability of IGBT, and minimizing the parasitic inductance of the package. It was found that the doping concentration’s effect on the diode’s peak forward voltage is not monotonic. It can be explained from the carrier density distribution during forward recovery transient that lower doping concentration reduces the carrier injection, and higher doping concentration reduces the excess carrier concentration in the doping region. Then, the influence of two buffer designs on the reverse blocking capability of IGBT was compared. It was found that a higher reverse blocking voltage would be achieved when a multi-proton implantation buffer replaced the diffused buffer. And the new design has almost no degradation in forward blocking capability.

The Influence to Uniform Current Distribution of SiC MOSFET Modules Based on the 3rd Quadrant Characteristics

This paper concentrated on the 3rd quadrant characteristics of 1200V/300A full SiC MOSFET modules produced by four SiC mainstream manufacturers; and compared the diode forward voltage (VSD) performances of “SiC MOSFET only” and SiC MOSFETs modules with SiC Schottky barrier parallel diode. The characteristics of the diode forward voltage showed that module A exhibits the same trend with the PiN diode, whereas modules B, C and D exhibit the characteristics of SBD. Through the failure analysis, it was verified that there is no parallel SBD in module A, meanwhile, it was assumed that modules B, C and D integrate a positive temperature characteristic SBD by wire bonding. The existence of SBD can prevent the modules from burning out due to excessive heating caused by non-uniform current distribution. From the analysis, it illustrated that the body diode can be used as the parallel SiC SBD, but further research on the uniform current distribution of the the body diode is needed.

Fully transparent GaN homojunction tunnel junction-enabled cascaded blue LEDs

A sidewall activation process was optimized for buried magnesium-doped p-GaN layers yielding a significant reduction in tunnel junction-enabled light emitting diode (LED) forward voltage. This buried activation enabled the realization of cascaded blue LEDs with fully transparent GaN homojunction tunnel junctions. The initial optimization of buried p-GaN activation was performed on PN junctions grown by metal organic chemical vapor deposition (MOCVD) buried under hybrid tunnel junctions grown by MOCVD and molecular beam epitaxy. Next the activation process was implemented in cascaded blue LEDs emitting at 450 nm, which were enabled by fully transparent GaN homojunction tunnel junctions. The tunnel junction-enabled multi-active region blue LEDs were grown monolithically by MOCVD. This work demonstrates a state-of-the-art tunnel junction-enabled cascaded LED utilizing homojunction tunnel junctions which do not contain any heterojunction interface.

Improved Bootstrap Methods for Powering Floating Gate Drivers of Flying Capacitor Multilevel Converters and Hybrid Switched-Capacitor Converters

A major challenge in the implementation of flying capacitor multilevel (FCML) converters and hybrid switched-capacitor (SC) converters is providing gate drive power to the large number of floating switches. A common solution uses isolated dc/dc converters, which are bulky, expensive, and energy inefficient. To design more compact and efficient gate drive power supply circuits, five methods are presented and compared in this article: bootstrap at deadtime, cascaded bootstrap with low-dropout (LDO) regulator, double charge pump, gate-driven charge pump, and synchronous bootstrap. By leveraging the inherent properties of multilevel converters, these methods can overcome the limitation of conventional bootstrap method (diode forward voltage drop) and make it possible to transfer ground-referenced power to all of the floating switches for any FCML or hybrid SC converters. Compared with the typical isolated dc/dc solution, these methods have simple structure and operating principle and can be implemented with a small number of diodes, capacitors, and LDOs. Experimental results show that an example power supply circuit can cut the size of the power stage of a state of the art seven-level FCML converter by half at 1/6 of the cost.

An AC–DC Rectifier With Active and Non-Overlapping Control for Piezoelectric Vibration Energy Harvesting

This brief presents an ac–dc rectifier for piezoelectric vibration energy harvesting application. The proposed rectifier is designed and implemented with TSMC 0.25 $\mu \text{m}$ 1P3M 5-V CMOS process. Active control is proposed to eliminate the voltage drop from the traditional diode forward voltage and the reverse current from the output capacitor to input source. The simultaneously turn on and oscillation on power MOS $M_{N1}-M_{N2}$ gate signal $V_{GN1}-V_{GN2}$ has been overcome by a 40-ns delay time which generated by a non-overlapping control. The experimental results indicated maximum power efficiency 95% and voltage conversion ratio 99% are achieved at 20 $\text{k}\Omega $ and 200 $\text{k}\Omega $ loading resistor.

Diode junction temperature in ultraviolet AlGaN quantum-disks-in-nanowires

The diode junction temperature (Tj) of light emitting devices is a key parameter affecting the efficiency, output power, and reliability. Herein, we present experimental measurements of the Tj on ultraviolet (UV) AlGaN nanowire (NW) light emitting diodes (LEDs), grown on a thin metal-film and silicon substrate using the diode forward voltage and electroluminescence peak-shift methods. The forward-voltage vs temperature curves show temperature coefficient dVF/dT values of −6.3 mV/°C and −5.2 mV/°C, respectively. The significantly smaller Tj of ∼61 °C is measured for the sample on the metal substrate, as compared to that of the sample on silicon (∼105 °C), at 50 mA, which results from the better electrical-to-optical energy conversion and the absence of the thermally insulating SiNx at the NWs/silicon interface. In contrast to the reported higher Tj values for AlGaN planar LEDs exhibiting low lateral and vertical heat dissipation, we obtained a relatively lower Tj at similar values of injection current. Lower temperatures are also achieved using an Infrared camera, confirming that the Tj reaches higher values than the overall device temperature. Furthermore, the heat source density is simulated and compared to experimental data. This work provides insight into addressing the high junction temperature limitations in light-emitters, by using a highly conductive thin metal substrate, and it aims to realize UV AlGaN NWs for high power and reliable emitting devices.

V2O5/4H-SiC Schottky Diode Temperature Sensor: Experiments and Model

Performances of temperature sensors based on Divanadium Pentoxide/4H polytype of silicon carbide, V2O5/4H-SiC, and Schottky diodes are analyzed. The devices with an active area of $1.96\times 10^{-3}$ cm2 were characterized in a temperature range between 147.22 and 396.75 K and in a current range between $1~\mu \text{A}$ and 1 mA. Measurements reveal that at a bias current of $16~\mu \text{A}$ , the diode forward voltage shows a linear dependence on the temperature, with a sensitivity of 1.86 mV/K and a temperature error of 0.64 K. Sensors have also shown a good repeatability of sensing over more cycles of measurements in the considered temperature range. Numerical simulations are performed, and device physical parameters are obtained from the best fit with experimental data. From simulation results, we show that the conduction mechanism of the sensor is affected by traps at the V2O5/4H-SiC interface, which have been modeled with an exponential tail. Moreover, device parameters, as epilayer doping concentration and thickness, have been varied in order to evaluate the variations on the sensor performances.

High Efficiency DC/AC/DC Converter Based on Synchronous Rectifier for Proton Exchange Membrane Fuel Cells

AbstractThis paper deals with the efficiency improvement of a DC/AC/DC converter used for proton exchange membrane fuel cell (PEMFC) coupling to an electrical vehicle DC bus. The power converter is based on a MOSFET inverter stage, a high frequency planar technology transformer stage and a full bridge diode rectifier output stage. The diode rectifier is a source of losses due to the diode forward voltage, which may be reduced by implementation of synchronous rectifier technology, especially for high output current. Mosfets with low drain‐to‐source on‐resistance are coupled to the diodes to reduce the losses. Control principle of this converter is presented with losses modeling and efficiency study in order to highlight the advantages of the synchronous rectification. Efficiency improvement is quantified from a comparison study with technological choices including silicon carbide (SiC) MOSFET and Schottky diodes. This study points out that the synchronous rectification becomes really relevant for an actual scale‐1 application and not for our reduced scale laboratory power converter. Finally, experimental validation of the control is presented with our laboratory test bench. The realization of a scale‐1 converter is under study to experimentally validate the advantages of the proposed synchronous rectification.

A Study of the Commercial Frequency Component and Doubled Component on the dc Side of Three‐Phase Rectifiers and Their Influence on Electric Railways

SUMMARYThis paper discusses nontheoretical harmonics on the dc‐side of a 12‐pulse rectifier in dc railway systems. These harmonics are the commercial frequency component and the doubled component. The causes of these harmonics are (a) diode forward voltage drop difference, (b) transformer secondary inductance difference, (c) voltage harmonics at the ac‐side of the rectifier, and (d) effects of the voltage induced by adjacent high‐voltage power transmission lines. We evaluated cases (a), (b), and (c), as case (d) has been previously studied . The results of the evaluation were as follows: · The effects of both the transformer secondary inductance difference and the voltage harmonics inside the electric power system are not negligible in some cases in the discussion of the EMC problem among railway equipments. · If there are several traction circuits in parallel, each of which consists of an input filter, an inverter, and several traction motors, the harmonic reduction effect of the filters weakens significantly.

Reliability modeling of Sn–Ag transient liquid phase die-bonds for high-power SiC devices

In this work, a novel foil-based transient liquid phase bonding process has been used to mount the SiC Schottky diodes. The Sn–Ag TLP interlayer material was produced in the form of preforms of multilayer foils, using electrochemical deposition. The foils were designed to keep the overall composition of Ag and Sn about 80% and 20% respectively. The optimized TLP bonding process parameters were used during the assembly process. The die-attachment characterizations revealed that resulting intermetallic compounds (Ag3Sn and ζ) have melting point beyond 480°C. The die-attachment produced low bending stresses, while heated from 30°C to 400°C. The reliability of Sn–Ag TLP bonded samples was studied during passive temperature cycling and during active power cycling. During power cycling, the crack rates were determined by measuring the crack lengths of the TLP bonded joints after failure. The failure criteria were set to be an increase of diode's forward voltage by 10% since the start of the power cycling tests. The thermo-mechanical simulations were performed to determine the damage parameter i.e. strain range amplitude ∆εp. Based on mechanical characterization of the TLP bonded layers, a plastic material model was used. The crack propagation rates were modeled using Paris' Law. Based on comparisons with state-of-the-art silver sintering technique, it can be stated that the TLP bonding is a promising die-attachment technique and its power cycling reliability is similar to silver sintering.

Impact of light-emitting diode chip material properties on photoelectric properties under low temperature

To study how light-emitting diode material properties impact its photoelectric characteristics at low temperature, the electrical performance of light-emitting diode chips was tested. Results of electrical performance testing of the die showed that the light-emitting diode forward voltage increases with decreasing temperature; this phenomenon is mainly caused by the material properties of the chip. Moreover, atomic force microscopy and scanning electron microscopy were used to examine crystal structure, surface morphology and layer arrangement, so as to further explore the relationship between photoelectric properties and chip material properties at low temperatures. It may be concluded that although the material properties of the chip can improve optical performance of light-emitting diodes at low temperature, they can also deteriorate the electrical performance and reduce the reliability and lifetime of the light-emitting diode chip.

The Effect of Light Ion Irradiation on 4H-SiC MPS Power Diode Characteristics: Experiment and Simulation

In this article, the effect of local radiation damage on the electrical characteristics of 1700 V 4H-SiC Merged-Pin Schottky (MPS) diode have been investigated. Radiation defects introduced by irradiation with 670 keV protons were placed into the low-doped n-type epi-layer and their influence on diode characteristics were characterized by capacitance DLTS, C-V profiling and I-V measurements. Simulation model accounting for the effect of proton irradiation was developed, calibrated and used for analysis of underlying effects and temperature dependencies. Results show that the forward voltage drop and breakdown voltage is insensitive to the position of the damage region when the defect peak is placed far away from the Schottky metal contact of the MPS diode. However, when the damage region approaches to the p <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> regions, forward voltage drop degrades significantly. For fluences higher than 3.3×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">- 2</sup> , the acceptor concentration in the peak region achieves donor doping level of the epi-layer and a sharp increase in the diode forward voltage drop is observed. Acceptor centers introduced by proton irradiation also slightly increase the breakdown voltage while decreasing the leakage current at voltages close to the MPS diode breakdown ( > 2000 V).

High-Input-Voltage High-Frequency Class E Rectifiers for Resonant Inductive Links

The operation of traditional rectifiers such as half-wave and bridge rectifiers in wireless power transfer applications may be inefficient and can reduce the amount of power that is delivered to a load. An alternative is to use Class E resonant rectifiers that are known to operate efficiently at high resonant frequencies and at large input voltages. Class E rectifiers have a near sinusoidal input current which leads to an improved overall system performance and increased efficiency, especially that of the transmitting coil driver. This paper is the first to investigate the use of Class E resonant rectifiers in wireless power transfer systems based on resonant inductive coupling. A piecewise linear state-space representation is used to model the Class E rectifier including the rectifying diode's forward voltage drop, its ON resistance, and the equivalent series resistance of the resonant inductor. Power quality parameters, such as power factor and total harmonic distortion, are calculated for different loading conditions. Extensive experimental results based on a 10-W prototype are presented to confirm the performed analysis and the efficient operation of the rectifier. An impressive operating efficiency of 94.43% has been achieved at a resonant frequency of 800 kHz.

Thermal Transient Effect and Improved Junction Temperature Measurement Method in High-Voltage Light-Emitting Diodes

The diode forward voltage method with pulsed currents was widely used for monitoring junction temperature (Tj) of light-emitting diodes (LEDs). However, a thermal transient effect (TTE) was observed by the pulsed currents and consequent errors were introduced. Thermoelectric physics was conducted to explain this phenomena and a group of experiments was used to reveal the TTE during Tj measurement for high-voltage (HV) LEDs. In addition, an improved pulse-free direct junction temperature measurement method was conducted for HV LEDs to reduce the errors and to achieve in situ Tj measurement with dc currents, simpler setups, and a less step sequence.

Transient thermal characteristics related to catastrophic optical damage in high power AlGaAs/GaAs laser diodes

The transient thermal characteristics related to catastrophic optical damage (COD) in high power AlGaAs/GaAs laser diodes (LDs) are studied experimentally by means of thermal infrared imaging, laser scanning confocal microscopy, and transient thermal technique. The transient thermal technique is based on the diode forward voltage method in which the structure function theory is applied to determine the component thermal resistance and temperature rise of the LDs. We have recorded the dynamics of COD process using thermal infrared camera. Two melting spots are observed in the output facet after COD which location exactly matches the position of the thermal flash from the thermal imaging and even the temperature of COD seed has a sudden increase of 32 K when the COD event occurs. Furthermore, we find that the thermal resistance from chip to In solder increases remarkably after COD, meanwhile the thermal resistance of solder and package does not change apparently. The results are attributed to the heat power dissipation increase originating from the enhancement of nonradiative recombination after COD under constant input electrical power.

Effect of Voiding in Solder Joints on Thermal Performance of the LED

Light-Emitting Diode (LED) lighting has potential to fundamentally alter lighting by replacing incandescent and fluorescent technologies because it offers significant energy saving, longer operational life, and many other advantages. Excellent thermal management and low-cost is vital for LED lighting to become the market standard for general lighting. The packaged LED is typically soldered to the metal-core printed circuit board (MCPCB). However, as the size of the packaged LED increases, voiding in solder joints becomes a major problem since voiding increases the thermal resistance. The research questions are: what is the effect of flux in solder paste and the LED size on the voiding? What is the relationship between the voiding and the thermal performance of the LED? In this study, packaged LEDs with three different sizes were assembled to MCPCBs using solder paste with two different types of fluxes. The voiding in solder joints was imaged by an X-Ray machine. The detailed void characteristics were analyzed. The LED's junction temperature was measured based on the diode's forward voltage junction temperature measurement method. The results show that both flux in solder paste and the LED size have significant effect on the voiding. There is weak positive correlation between the voiding and the thermal performance when the voiding is over 25% coverage. However, the effect of voiding on the thermal performance is insignificance when the voiding is less than 25% coverage.

The thermal properties of AlGaAs/GaAs laser diode bars analyzed by the transient thermal technique

The thermal properties of AlGaAs/GaAs laser diode bars have been analyzed in detail by transient thermal technique based on the diode forward voltage method on the vertical and horizontal thermal conduction paths, respectively. On the vertical thermal conduction path, it is found that the steady-state temperature rise of the central emitter among operated emitters has a linear relationship with the logarithm of the total operating current. The time constant determined for chip decreases with the total operating current, while the time constant determined for solder/heat sink interface and package remains almost constant. In addition, the effective thermal diffusivity of chip increases with total operating current. On the horizontal thermal conduction path, the time constant varies linearly with the distance increasing, and the effective thermal diffusivity remains almost constant. The results suggest that the thermal crosstalk between emitters increases with the total operating current.

Study the Effect of Junction Temperature on the Peak Wavelength in GaN-Based High-Power Green Light Emitting Diodes

The junction temperature of GaN-based high-power green light emitting diodes is measured using the temperature coefficients of the diode forward voltage, from changes in temperature and changes in drive current to measure the LED junction temperature and the corresponding spectral, Respectively. Experiments show that, junction temperature due to environmental temperature increased, and the red shift of the spectral peak wavelength. When low temperature or less then the rated current range, the drive current increased in junction temperature rise due to the spectral peak wavelength blue shift . When the current is increased in the range of close to or greater than the rated current, leading to the junction temperature rise will cause spectral red shift . The peak wavelengths’ shift degree of 0.0579nm / k, 0.0751 nm / k and-0.1974nm / k, -0.0915 nm / k are calculated in both cases. The phenomenon is due to the LED junction temperature increases lead to band gap shrinkage, and the result of the role of spontaneous polarization and piezoelectric polarization in Ⅲ-nitride semiconductor materials.

Silicon on Insulator Diode Temperature Sensor– A Detailed Analysis for Ultra-High Temperature Operation

Silicon diodes can be used for accurate temperature monitoring up to higher temperatures in a variety of sensors such as micro-machined resistive and calorimetric gas sensors, thermal flow sensors, exhausts, etc. This paper investigates the performance of a diode temperature sensor when operated at ultra high temperatures (up to 780°C ). A low leakage silicon on insulator (SOI) diode was designed and fabricated in a 1.0 ¿m CMOS (complementary metal oxide semiconductor) process. The diodes were suspended within a dielectric membrane [formed by post CMOS deep reactive ion etching (DRIE)] for efficient thermal insulation. A CMOS compatible micro-heater was integrated with the diode on the dielectric membrane for local heating. It was found that the diode forward voltage exhibited a linear dependence on temperature as long as the reverse saturation current remained below the forward driving current. We show experimentally that the maximum temperature up to which the linearity of diode's forward voltage output is maintained can be as high as 550°C . Long term continuous operation at high temperatures (400°C and 500°C ) showed good stability of the diode voltage drop. Finally, we present a detailed theoretical analysis that helps to determine the maximum operating temperature for the diode and also explains the presence of nonlinearity factors in diode voltage output at ultra high temperatures.

Thermal Analysis of InGaN/GaN Multiple Quantum Well Light Emitting Diodes with Different Mesa Sizes

We analyze experimentally and theoretically the thermal characteristics of 470 nm InGaN/GaN light emitting diodes (LEDs) with different mesa sizes for efficient heat dissipation. For various mesa sizes, the junction temperature is measured as a function of injection current by the diode forward voltage method. The junction temperature (Tj) increases linearly with injection current and it rises rapidly with the reduction in mesa size. The thermal parameters, such as the junction temperature, temperature profile, and thermal resistance (Rth), are obtained from thermal simulations with the heat source density, determined from the measured light–current–voltage data, using a three dimensional heat dissipation model. At 200 mA, the Tj values of LEDs are theoretically calculated as 392.7 and 578 K for 450 ×450 and 250 ×250 µm2, respectively. The thermal resistance is kept nearly constant due to a linear relationship between junction temperature and injection current and it is reduced as the mesa size increases, indicating a low Rth of < 75 K/W for 450 ×450 µm2 LED. The Rth values obtained by the thermal simulation are fairly consistent with the experimental data. The use of the substrate with a relatively high thermal conductivity can also improve significantly the Rth of LEDs.