Modern Power Electronic Devices Research Articles

III-Nitride Magnetron Sputter Epitaxy on Si: Controlling Morphology, Crystal Quality, and Polarity Using Al Seed Layers.

Group III-nitride semiconductors have been subject of intensive research, resulting in the maturing of the material system and adoption of III-nitrides in modern optoelectronics and power electronic devices. Defined film polarity is an important aspect of III-nitride epitaxy as the polarity affects the design of electronic devices. Magnetron sputtering is a novel approach for cost-effective epitaxy of III-nitrides nearing the technological maturity needed for device production; therefore, control of film polarity is an important technological milestone. In this study, we show the impact of Al seeding on the AlN/Si interface and resulting changes in crystal quality, film morphology, and polarity of GaN/AlN stacks grown by magnetron sputter epitaxy. X-ray diffraction measurements demonstrate the improvement of the crystal quality of the AlN and subsequently the GaN film by the Al seeding. Nanoscale structural and chemical investigations using scanning transmission electron microscopy reveal the inversion of the AlN film polarity. It is proposed that N-polar growth induced by Al seeding is related to the formation of a polycrystalline oxygen-rich AlN interlayer partially capped by an atomically thin Si-rich layer at the AlN/Si interface. Complementary aqueous KOH etch studies of GaN/AlN stacks demonstrate that purely metal-polar and N-polar layers can be grown on a macroscopic scale by controlling the amount of Al seeding.

Enhancing energy storage performance of polyethylene via passivation with oxygen atoms through C–H vacancy carbonylation

Low energy density of polymer film capacitors is regarded as one of the most serious drawbacks facing growing demands for equipment integration and miniaturization. Herein, ultraviolet light and ozone (UVO) surface modification is utilized to simultaneously improve dielectric constant and breakdown strength of polyethylene (PE) films. As a result, after 3 min of UVO treatment, an enhanced recoverable energy density of 4.79 J/cm3 with a charge-discharge efficiency of >95% is obtained under 650 MV/m at room temperature (RT). Significantly, stable energy storage performance under 200 MV/m is maintained throughout a broad temperature range from −90 °C to 90 °C and during 20,000 cycles of charge-discharge procedures. According to first-principles calculations and thermally stimulated depolarization current measurements, formation of carbonyl groups (C=O) after UVO treatment could effectively passivate initial deep-level defect states caused by H vacancies, which explains the improvement in capacitive energy storage. Moreover, the metalized UVO-modified PE exhibits valuable breakdown self-clearing ability, and the self-cleared specimen maintains stable energy storage performance over 20,000 cycles at 200 MV/m and RT. This work offers an effective and user-friendly method for enhancing comprehensive dielectric characteristics of PE-based materials and potential for applications in modern power systems and electronic devices.

Simultaneous Inhibition of Conduction Loss and Enhancement of Polarization Intensity of Polyetherimide Dielectrics for High-Temperature Capacitive Energy Storage.

Polymer dielectrics with excellent high-temperature capacitive energy storage performance are in urgent demand for modern power electronic devices and high-voltage electrical systems. Nevertheless, the energy storage capability usually degrades dramatically at increased temperatures, owing to the exponentially increased conduction loss. Herein, a trace of commercially available aluminum nitride (AlN) nanoparticles is incorporated into the poly(ether imide) (PEI) matrix to inhibit the conduction loss. The nanostructured AlN component with a large specific surface area can provide abundant sites for the collision of carriers. More importantly, the generated new trap energy levels can immobilize the carriers, accordingly contributing to the reduction in leakage current. From this, the discharged energy density at 150 °C of PEI composites increases by 82.13% from 2.63 J/cm3 for pristine PEI to 4.79 J/cm3 for PEI composites. This work establishes a facile approach to enhancing the high-temperature capacitive performance of polymer dielectrics.

Excellent energy storage properties with ultrahigh Wrec in lead-free relaxor ferroelectrics of ternary Bi0.5Na0.5TiO3-SrTiO3-Bi0.5Li0.5TiO3 via multiple synergistic optimization

Advanced energy storage capacitors play important roles in modern power systems and electronic devices. Next-generation high/pulsed power capacitors will rely heavily on eco-friendly dielectric ceramics with high energy storage density (Wrec), high efficiency (η), wide work temperature range and stable charge-discharge ability, etc. Lead-free Bi0.5Na0.5TiO3 (BNT) based relaxor ferroelectric (RFE) ceramics are considered as one of the most promising candidates for energy storage capacitors. However, the application fields of them are greatly limited by their relatively low Wrec (generally <5 J/cm3). In this paper, excellent energy storage properties characterized by a great breakthrough in Wrec are achieved in a novel BNT system, (1-x)BNT-x(0.7SrTiO3-0.3Bi0.5Li0.5TiO3)+0.5 at.%Nb2O5 (x = 0, 0.1, 0.2, 0.3, 0.4), by synergistically constructing highly dynamic polar nanoregions (PNRs) and nanodomains, ultrafine grains (submicron size) and intrinsic conduction. Of great importance, the x = 0.4 ceramic exhibits an ultrahigh Wrec of 8.63 J/cm3 as well as a high efficiency (ƞ) of 89.6 % under a giant electric field of 520 kV/cm, due to coexistence of ultrahigh polarization difference (ΔP=Pmax −Pr) and high dielectric breakdown electric strength (Eb). Furthermore, excellent temperature stability (20−180 °C), frequency stability (1 − 500 Hz), and cycling stability (1 − 105 times) with the variation of Wrec < ±4 % and η < ±3 % are also found in the x = 0.4 ceramic. These results demonstrate that it is a very promising lead-free dielectric capacitor with enormous energy storage applications.

In-situ delamination detection in multi-layered semiconductor packages

Accurately determining the material properties of large-area solder joints is crucial for developing precise lifetime models in modern power electronic devices, as these joints play a vital role in providing both electrical and mechanical connections between components. This study presents a novel, non-destructive, and in-situ technique based on laser Doppler vibrometry for detecting crack initiation and monitoring crack growth in semiconductor structures. This method was successfully applied to determine various stages of die attach degradation during accelerated mechanical cyclic tests of large area solder joints, and was verified by scanning acoustic microscopy (SAM) measurements as well as optical methods. Furthermore, analysis of the acoustic emission (AE) signal was conducted as an alternative method for monitoring crack propagation. Optical and electron microscopy were employed to analyse crack initiation, crack paths, and crack surface morphologies. The in-situ delamination detection technique can provide essential information for robust lifetime prediction modelling of material systems in advanced semiconductor components.

Investigation of the effect of different types of SiN layers and cap-GaN on the surface electronic states of AlGaN/GaN heterostructures with 2DEG using X-ray and UV photoelectron spectroscopy

Determining the effect of different crystalline and amorphous passivation layers on the electronic states and surface properties of III-nitride heterostructures is an important task from the point of view of improving the performance of modern microwave and power electronic devices. In the present work the effect of in situ deposited gallium nitride and silicon nitride passivation layers on the surface electronic states of AlGaN/GaN heterostructures with a two-dimensional electron gas is investigated using the X-ray, ultraviolet and angle-resolved ultraviolet photoelectron spectroscopy (XPS, UPS, ARUPS) techniques. A thorough analysis of the experimental UPS spectra was carried out, the primary photoelectrons were extracted from the experimental spectra and the contribution of the electron states on the surface in the energy range of the AlGaN bandgap was identified. It was found that the density of states on the surface decreases by about an order of magnitude in the AlGaN bandgap during the formation of a silicon nitride layer. For the first time, it was found that a significant decrease in the density of surface states (up to a factor of 6) is observed even at extremely low thickness of the SiN ordered layer formation with the (√3 × √3)R30° superstructure.

Characterization of Supraharmonic Emission from Three Different Electric Vehicle Charging Infrastructures in Time and Frequency Domain

With the recent proliferation of electric vehicles (EVs), maintaining power quality within acceptable limits in future distribution grids will become a challenging task. A specific concern is the spread of Supraharmonics in the range from 2 to 150 kHz, generated by modern power electronic devices. In this paper, the long term Supraharmonic distortion from three differently sized electric vehicle charging infrastructures is analyzed in frequency and time domain. At the monitored sites several interruptions of EV charging processes were observed due to poor power quality. It was found that vehicles disconnect when exposed to high levels of harmonic distortion. Moreover, the impact of the charging EVs on the Supraharmonic distortion and the interaction with the background distortion for the individual sites is discussed. Results show that a general increase in Supraharmonics emission can be expected due to the rising number of EVs. However, measurements also indicate that damping effects can occur for certain load configurations.

Ultraflexible polyamide-imide films with simultaneously improved thermal conductive and mechanical properties: Design of assembled well-oriented boron nitride nanosheets

The highly thermally conductive yet electrically insulating polymeric materials are exhibiting tremendous potential for thermal management materials. However, the practical application of these materials is restrained by the limited thermal conductivity (TC) and deterioration of mechanical properties. In this work, an ultraflexible polyamide-imide (PAI) film with a sandwich-like structure composed with assembled well-oriented functionalized boron nitride nanosheets (FBN) by facile layer-by-layer solution-coating strategy is constructed. The design of the layered structure and highly oriented arrangement of interconnected FBN (Herman's orientation parameter ƒ up to 0.847) endows the obtained PAI composite film with super-flexibility, ultrahigh in-plane thermal conductivity (λ//), superior thermal transfer capability (ΔTmax = 24.4 °C) and excellent electrical insulation performance. The PBP composite film reaches an ultrahigh λ//of 45.7 W m−1 K−1 with only 23 wt% FBN loading and exhibits a remarkable TC enhancement factor over 23 because of the more continuous phonon transfer networks that constructed by interconnected well-oriented FBN which could effectively suppress the phonon scattering. Furthermore, the mechanical properties of the layered composite film (PB4P) exhibit noteworthy enhancement compared with uniform PBN composite film, in which the tensile strength is increased by 110% and toughness enhancement is 329%. Meaningfully, our fabrication strategy has the advantage of simplicity and adaptability for commercial amplification. The composite film developed in this work provides a promising prospect for the thermal management system of modern power electronic devices.

Modern Power Electronic Devices: Physics, Applications, and Reliability [Book News

This book discusses silicon and wide bandgap (WBG) semiconductor-based devices. After the preface, it includes 14 carefully selected chapters to cover recent trends in WBG semiconductors, with the following subjects: power electronics challenges, junction diodes, Si MOSFETs, Si IGBTs, SiC MOSFETs, GaN transistors, module design and reliability, switching cell design, and prospects and outlooks for the power electronics technology. This high-quality book is illustrated with hundreds of highly pedagogical color figures, where important features are easily visible. A table of contents, a note about the editor, a preface, and an index are also present.

Black-box identification of grid-side filter circuit for improved modelling of single-phase power electronic devices for harmonic studies

This paper presents an identification methodology for filter circuits of commercially available power electronic devices based on laboratory measurements. The filter circuit is one of the main components with significant impact on the harmonic behaviour, in particular for modern power electronic devices. The generic approach does not require detailed knowledge about the circuit layout and is applicable for all single-phase power electronic devices where a voltage measurement on both sides of the filter circuit is possible. Current measurements on the circuit board, which are usually not practicable, are not required. The model parameters of the filter circuit are represented by two admittances for each considered frequency. The parameter identification is based on the analysis of the frequency couplings of power electronic devices. The proposed method is validated by simulations and exemplarily applied for a commercially available photovoltaic (PV) inverter in the laboratory. The measurement-based parameter identification can also provide more reliable results compared to the white-box simulation of a particular device, as the partly large manufacturing tolerances of the elements are inherently considered in the measurements.

Analysis of Dislocations in PVT-Grown 6H-SiC through Grazing-Incidence X-Ray Topographic Images and Ray-Tracing Simulation

The superior electronic and physical properties of silicon carbide (SiC), such as wide band-gap, high saturated electron velocity, high breakdown electric field strength, and high thermal conductivity, enable successful applications in modern power electronic devices with high power, high frequency, and high temperature operation requirements. [1,2] Therefore, understanding the nature and behavior of different dislocations is of great significance towards crystal quality enhancement. Synchrotron X-ray has been widely adopted for generating topographic images of threading screw dislocations (TSDs) as well as threading edge dislocations (TEDs) and basal plane dislocations (BPDs). Besides, recent study in 4H-SiC revealed the presence of threading mixed dislocations (TMDs) with Burgers vectors nc+ma (where m and n are integers). [3] Since direct TMDs observation methods such as transmission electron microscopy (TEM) and synchrotron white-beam X-ray topography (SWBXT) are not suitable for commercially preferred c-plane-oriented wafers, ray-tracing simulated images of possible dislocation types are compared with X-ray topographs in order to identify the TMDs non-destructively. Except 4H-SiC, ray-tracing simulation has also been proved as an effective approach for dislocation characterization in various materials such as GaN [4], ZnO [5], and AlN [6]. The same principle is implemented in this study for the investigation of dislocations in 6H-SiC wafer.Synchrotron monochromatic beam X-ray topography (SMBXT) analysis was carried out on a PVT grown 6H-SiC wafer for recording its grazing-incidence images of all six different 11-212 reflections (Fig. 1). The distribution of TSDs, TEDs, TMDs, and BPDs are characterized, and the determination of their Burgers vectors is achieved by correlating the simulated results obtained through ray-tracing simulation with real X-ray topographic observations (Fig. 2). This study provides a clear understanding of dislocations in 6H-SiC, which is crucial for quality improvement of the crystal.Reference:[1]: C. Codreanu, et al, Comparison of 3C-SiC, 6H-SiC and 4H-SiC MESFETs Performances, Materials Science in Semiconductor Processing 3 137 (2000).[2]: J. W. Sun, et al, Shockley-Frank Stacking Faults in 6H-SiC, Journal of Applied Physics 111, 113527 (2012).[3]: J. Q. Guo, et al, Direct Determination of Burgers Vectors of Threading MixedDislocations in 4H-SiC Grown by PVT Method, Journal of Electronic Materials 45, 4 (2016).[4]: B. Raghothamachar, et al, X-ray Topography Characterization of Gallium Nitride Substrates for Power Device Applications, submitted for publication.[5]: T. Y. Zhou, “Threading Dislocation Characterization and Stress Mapping Depth Profiling via Ray Tracing Technique,” Ph.D. Thesis, SUNY Stony Brook, Advisor: Michael Dudley (2015).[6]: T. Y. Zhou, et, al, Characterization of Threading Dislocations in PVT-Grown AlN Substrates via x-Ray Topography and Ray Tracing Simulation, Journal of Electronic Materials volume 43, 838 (2014). Figure 1

Structural, optical and impedance spectroscopy study of thin film of polyaniline (PANI/ZnO) nanocomposite

Modern organic electronic and power electronic devices gained attention due their superior performance and efficiency with reduced cost. While nanocomposites of these organic semiconductors have high potential to further enhance these properties. In this work, thin films of zinc oxide-polyaniline (ZnO-PANI) nanocomposite with different compositions of ZnO (50, 60 and 70 wt%) are deposited by spin coater onto the surface of p-Si. The phase identification of the samples is identified through x-ray diffraction analysis. Pure ZnO showed wurtzite crystalline while PANI and nanocomposites of ZnO-PANI showed amorphous structure. The optical absorption band gap was evaluated from Ultraviolet–visible spectroscopy absorption studies and band gaps were calculated from Tauc’s plots. The Ultraviolet–visible spectroscopy showed that by increasing ZnO content in the nanocomposite, the band gap increases from 3.25 eV to 3.3 eV and 3.4 eV for 50–50, 60–40 and 70–30 wt% respectively. The AC electrical properties of the nanocomposites were studied by using impedance spectroscopy. The parameters extracted from the impedance plots and conductivity values showed that 50–50 wt% is more conductive while that of 70%–30% wt is more resistive.

Smart Lighting Systems as a Demand Response Solution for Future Smart Grids

Massive deployment of distributed and intermittent renewable energy sources cause instability in the power system because of the mismatch between the power generation and load consumption. In order to solve this problem, smart loads embedded with modern power electronic converters and communication devices are being developed. They are able to communicate with the utility and perform automatic demand response. In this paper, we propose a smart light-emitting diode (LED) driver for lighting. This smart LED driver adjusts its electricity usage in response to the utility without the expense of human visual comfort. To achieve this goal, a new control method is developed and a typical rate of change of LED power is determined through conducting a series of visual assessments with interviewees. An experimental smart LED driver is built to validate the new control method. Experimental report from the visual assessments has confirmed that the proposed control method can significantly reduce the light flickering caused by the change of LED power.

A dual-output magnetoelectric gyrator

A novel dual-output magnetoelectric (ME) gyrator operating in an acoustic resonance mode and based on a Pb(ZrxTi1−x)O3 (PZT)/Metglas/PZT (P–M–P) trilayer structure is discussed. The dual-output with different current-to-voltage (I–V) conversion ratios and different voltage levels result from the use of piezoelectric layers with different thicknesses as the output capacitive port. Under open circuit conditions, the maximum I–V conversion ratios of the two outputs were 5.7 and 13.5 kV A−1 at a frequency of 50.4 kHz. A high power efficiency (ƞ) of 91.7% was achieved and remained relatively stable (⩾86%) under increasing power drive to a power density of 45 W in−3. These excellent power transfer and multi-output characteristics offer unique possibilities for possible use of ME gyrators in modern power electronic devices.

Effect of Wafer Orientation on Near-Interface Oxide Traps in 4H-SiC Metal-Oxide-Semiconductor Capacitors

4H-Silicon carbide is one of the enabling materials for modern high voltage and high temperature power electronic devices due to its attractive material properties. A significant drawback to SiC MOSFET performance is the low channel conductance due to trapping of carriers by the high-density of near-interface traps (NITs) at the SiO2/4H-SiC interface. These states are spatially located within ~1 nm from the interface and energetically positioned near the conduction band edge of 4H-SiC. Constant capacitance deep level transient spectroscopy (CCDLTS) technique is appropriate for analysis of such defects as it can differentiate between trap types and measure trapped charge emission rates. In this study, we examined SiO2-4HSiC interfaces formed on the polar (0001) Si- face (100% Si) and non-polar (11-20) a-face (50% Si, 50% C) oriented 4H-SiC wafers using CCDLTS. For the NO annealed Si-face interface, there are two main types of NITs detected by CCDLTS, labeled “O1” and “O2” traps by Basile et al. [1]. The physical identities of these defects have been suggested to be carbon dimers substituted for O dimers (CO=CO) and interstitial Silicon atoms in the near interfacial SiO2[2]. In this work, we observed both the O1 and O2 traps in the Si-face with activation energies of about 0.15±0.01 eV and 0.35±0.01 eV respectively, which are consistent with previous results[3]. The original result obtained in this study was that for the a-face; two new NITs (labeled A1 & A2) positioned very close to the O1 peak were observed but the O2 peak was absent. For this study, 4H-SiC MOS capacitors were fabricated on Si-face and a-face oriented wafers. The samples underwent dry oxidation followed by nitridation with NO annealing at 1175°C. After that, circular Al gates were evaporated as gate contact. The oxide thickness was ~62 nm and ~54 nm for Si-face and a-face respectively. CCDLTS was measured on capacitors keeping a constant capacitance in deep depletion in a temperature range of 77 K to 298 K changing pulse voltages and emission rates. Using the analysis method detailed in [1], the activation energies of the A1 and A2 peaks were found to be 0.15±0.01 eV and 0.19±0.01 eV respectively, which is in the same range as the O1 trap in the Si-face. The capture cross-sections for all traps detected was in the 10-16-10-14 cm2 range. Qualitatively, this result is similar to the results reported in [4], which shows that nitrided SiO2 formed on the (000-1) C-face (100% C terminated) also shows only one peak very similar to the O1 trap observed on the Si-face. This result points to the importance of interface structural differences due to different wafer orientation with respect to near-interface oxide traps. Acknowledgement: This work was supported by the II-VI foundation

On Evaluation of Power Electronic Devices’ Efficiency for Nonsinusoidal Voltage Supply and Different Operating Powers

This paper analyses the impact of operating modes and nonideal power supply conditions on the efficiency of modern low-voltage power electronic devices. The sophisticated circuits and controls implemented in such devices are expected to result in increased efficiencies, higher operating power factors, and reduced harmonic emissions. However, the interactions of individual PE devices with the supplying network will impact exchanges of powers at fundamental system frequency and nonfundamental (i.e., harmonic) frequencies. This paper correlates the obtained results for harmonic performance and efficiencies over the entire range of operating powers of the considered PE devices using both standard definitions and some alternative interpretations.

An Innovative Extinction Angle Control Technique for Soft Starting the Three Phase Squirrel Cage Induction Motor

The time old conventional starting schemes though have been in use for many years exhibit some drawbacks and such drawbacks can be overcome only with power electronic motor starters. The advent of modern power electronic devices and the control systems supported by modern digital processing units have led to the development of digital power electronic soft starting schemes that guaranteed higher degrees of compliance of the requirements of an ideal soft starter for the induction motor. This research paper presents the results of the comparative study of the two versions of soft starting schemes viz the phase angle control and extinction angle control and brings about the highlights, by way of MATLAB / SIMULINK based simulation and experimental verification, and the advantages of the extinction angle control.

Induction Machine Insulation Health State Monitoring Based on Online Switching Transient Exploitation

Today's variable-speed drives are usually operated close to their maximum tolerable conditions. The fast switching of modern power electronic devices leads to high stress of the winding insulation. As a result, an insulation breakdown may lead to sudden breakdown and high economic loss. To avoid unpredictable downtimes and enable repair on demand, monitoring of the insulation health state is getting more and more important. This paper proposes a method to monitor changes in the insulation health state by evaluating the machine high-frequency properties. The deterioration of the insulation condition is usually linked with a change of insulation capacity and thus also influences high-frequency properties. Initiating a voltage step excitation of the machine by the switching of the inverter, the high-frequency properties can be identified by measuring the resulting current response. This response is usually seen as current signal ringing and contains the machine high-frequency information. By applying signal processing tools, changes in the high-frequency information are extracted, and an insulation state indicator is derived. The applicability of the method is verified by measurements on two test machines (5.5 kW and 1.4 MW) having different power ratings as well as different insulation systems.

Adaptive distance protection setting in presence of mid-point STATCOM using synchronized measurement

Abstract EHV and HV transmission lines are used widely to transfer power from power generating area to large load centers. Nowadays compensating devices which uses modern power electronic devices are mostly used to improve the power transfer capability of transmission lines. Use of FACTS devices in transmission lines affect protection system very drastically. In this paper, the issues related with distance protection of transmission lines with STATCOM connected at mid-point are addressed. To mitigate the problems associated with distance protection, a novel algorithm based on synchronized measurement for adaptive relay setting is proposed. The power system is modeled in EMTDC/PSCAD software with frequency dependent model of transmission line. The results obtained for the new adaptive setting scheme are accurate, robust and superior in comparison with those obtained from existing distance protection schemes for transmission line with STATCOM.

Minimization and identification of conducted emission bearing current in variable speed induction motor drives using PWM inverter

The recent increase in the use of speed control of ac induction motor for variable speed drive using pulse width modulation (PWM) inverter is due to the advent of modern power electronic devices and introduction of microprocessors. There are many advantages of using ac induction motor for speed control applications in process and aerospace industries, but due to fast switching of the modern power electronic devices, the parasitic coupling produces undesirable effects. The undesirable effects include radiated and conducted electromagnetic interference (EMI) which adversely affect nearby computers, electronic/electrical instruments and give rise to the flow of bearing current in the induction motor. Due to the flow of bearing current in the induction motor, electrical discharge machining takes place in the inner race of the bearing which reduces the life of the bearing. In high power converters and inverters, the conducted and radiated emissions become a major concern. In this paper, identification of bearing current due to conducted emission, the measurement of bearing current in a modified induction motor and to minimize the bearing current are discussed. The standard current probe, the standard line impedance stabilization network (LISN)), the electronics interface circuits are used to measure high frequency common mode current, bearing current and to minimize the conducted noise from the system. The LISN will prevent the EMI noise entering the system from the supply source by conductive methods, at the same time prevents the EMI generated if any due to PWM, fast switching in the system, will not be allowed to enter the supply line. For comparing the results with Federal Communications Commission (FCC) and Special Committee on Radio Interference (CISPR) standards, the graphs are plotted with frequency Vs, line voltage in dBµ V, common mode voltage in dBµ V and the bearing current in dBµ A with out and with minimizing circuits.