Characteristics Of Power Devices Research Articles

Low-resistance TiAl3/Au ohmic contact and enhanced performance on AlGaN/GaN HEMT

The advent of an era characterized by intelligent, interconnected systems of AlGaN/GaN High Electron Mobility Transistors (HEMTs) electronic devices is underway. Within this context, the performance of ohmic contacts in HEMTs bears substantive influence on the electrical characteristics of power devices, notably impacting parameters such as on-resistance and output current. Therefore, the improvement of ohmic contacts attributes in AlGaN/GaN HEMT devices has perennially constituted a focal point of considerable industry. Based on the AlGaN/GaN heterostructure, a novel TiAl3/Au ohmic contact has been successfully developed for HEMTs. A low contact resistance of 0.23 Ω·mm (2.33 × 10-6 Ω·cm2) is obtained, which proposes a new interface contact for AlGaN/GaN heterojunction. Transmission electron microscope (TEM) illustrates that the contact mechanism for low resistance is direct contact with two-dimensional electron gas (2DEG) through the substitution of the TiN compound with a smaller area Au dominated penetration. Concurrently, in contrast to TiN, Au exhibits a diminished capacity for Ga dissolution, thereby substantiating its efficacy in preserving the structural integrity of the crystal lattice. In addition, the reduction of Al can impede the diffusion notably, further showing the smooth surface morphology of the electrode with atomic force microscope (AFM) and scanning electron microscopy (SEM) measurements. The ohmic contacts of HEMTs are individually fabricated with Ti/Al/Ni/Au and TiAl3/Au configurations. The HEMTs with TiAl3/Au ohmic contacts demonstrate superior DC characteristics.

The Cascade of High-Voltage Pulsed Current Sources

Currently, pulsed adders are used as pulsed voltage sources maturely. However, their use as pulsed current sources is significantly limited due to circuit impedance and the characteristics of power devices. This paper presents a simple yet effective design for a pulsed current source, incorporating a solid-state Marx pulsed adder as the primary power source and an inductor for energy storage. In the pulsed current source, a Marx pulsed adder produces high voltage to charge the inductor. Then, the stored inductance energy is converted to generate current pulses on the load; the amplitude of the pulsed current is unaffected by the load impedance within a certain range. The pulsed current source can be designed as a standard module, and several modules can form a cascade system for producing current pulses with higher voltage. Finally, a pulsed current source was developed, which can produce adjustable current pulses with high voltage. The design principles, control methods and the effects of the distribution parameters are described. The feasibility of the cascade pulsed power system was validated in experiments. Nine modules were connected to generate pulses of current 10 A on a 15 kΩ resistor.

Electro-thermal stress minimisation of motor-drive inverter switches by hybrid modulation strategy technique

This paper proposes the application of different modulation strategies to the inverter used in a motor-drive, depending on the wide operational point, to minimise the electro-thermal stress of the semiconductor devices and other components in the system. As a case study, a multi-level SiC inverter is considered, derived from an actual industrial product. Using the proposed hybrid modulation, results indicate that considerable reduction of inverter energy losses can be achieved during cycle, depending on the switching frequency, and power device characteristics.

Comparative Study of IGBT and SiC MOSFET Three-Phase Inverter: Impact of Parasitic Capacitance on the Output Voltage Distortion

This study investigates the nonlinearities in three-phase inverters for SiC-based systems and compares their performance to IGBT-based systems. An analytical model of inverter voltage distortion is developed, which accounts not only for dead time (td), switching delay time, switching frequency (fs), and voltage drops of power devices, but also for output parasitic capacitance (Cout). Experimental tests validate the model, which provides a more accurate estimate of the inverter’s output phase voltage distortion. The power device characteristics are obtained from datasheets, while Cout is determined through experimentation. Three-phase inverters with varying switching frequencies, fundamental frequencies, and dead-time values are used in simulations and experiments to determine the influence of nonlinearity on phase voltage deviation and current distortion. The results show that, due to SiC devices’ faster switching time, the phase voltage deviation and phase current distortion are lower in SiC-based inverters than in IGBT-based ones for high-frequency applications, as the dead time can be reduced.

Demonstration of SiC Trench Gate MOSFETs with Narrow Cell Pitch Using Source Self-Aligned Process

The SiC trench gate MOSFET with narrow cell pitch is demonstrated using a process in which the n+ source is self-aligned to the trench gate. A minimum cell pitch of 1.6 μm, which is difficult to achieve using the conventional device structure, is easily fabricated by applying a deep n+ source and a buried interlayer dielectric structure. The cell pitch reduction indicates a beneficial trend that contributes to a decrease in the specific on-resistance and an increase in the breakdown voltage. The process and structure are promising for further improving SiC power device characteristics.

Evaluation of Line-Shape Defect in Epitaxial Wafer

In this study, we investigated the origin of line-shape defect in 4H-SiC epitaxial wafers. The inspection results revealed that such defects resulted from the substrate entirely and accompanied with dislocation lines during the epitaxial process. Although the defect surface condition with nanometer level of roughness seemed to do little harm to the initial electrical characteristics of power devices, dislocation lines possibly resulted in high leakage current when reverse voltage was applied. To reduce line-shape defects, it is essential to reduce defects and threading dislocations in substrates and to develop a nondestructive method for wafer screening.

Active Auto-Suppression Current Unbalance Technique for Parallel-Connected Silicon Carbide MOSFETs

Nowadays, medium- and high-power applications make use of silicon carbide (SiC) MOSFETs, and many times their parallelization is necessary. Unfortunately, this requirement causes an inevitable current unbalance between power devices, affecting the performance of power switches. Over the last decade, numerous studies have been conducted, proposing various techniques with the capability of mitigating current unbalance for a number of discrete parallel SiC MOSFETs. However, the realization of most methods requires knowledge of the technical characteristics of power devices, adding extra cost to the system, since screening is a time-consuming and costly process. This necessity reduces the possibilities of such a technique being implemented in power electronics applications, preventing the exploitation of the exceptional features of SiC MOSFETs. In addition, most of these techniques can suppress only the current unbalance, which occurs during turn-on and turn-off transitions. In this paper, an active auto-suppression current unbalance technique is proposed, requiring no device screening. The active method is a closed-loop system capable of sensing and eliminating the entire current unbalance between parallel SiC MOSFETs automatically, actively, and independently of the cause. Simulation results are presented to demonstrate the feasibility and effectiveness of the proposed technique.

Silicon carbide power device characteristics, applications and challenges: an overview

Silicon (Si) based power devices have been employed in most high power applications since decades ago. However, nowadays, most major applications demand higher efficiency and power density due to various reasons. The previously well-known Si devices, unfortunately, have reached their performance limitation to cover all those requirements. Therefore, Silicon Carbide (SiC) with its unique and astonishing characteristic has gained huge attention, particularly in the power electronics field. Comparing both, SiC presents a remarkable ability to enhance overall system performance and the transition from Si to SiC is crucial. With regard to its importance, this paper provides an overview of the characteristics, advantages, and outstanding capabilities in various application for SiC devices. Furthermore, it is also important to disclose the system design challenges, which are discussed at the end of the paper.

System Efficiency Improvement for Electric Vehicles Adopting a Permanent Magnet Synchronous Motor Direct Drive System

To improve the endurance mileage of electric vehicles (EVs), it is important to decrease the energy consumption of the Permanent Magnet Synchronous Motor (PMSM) drive system. This paper proposes a novel loss optimization control strategy named system efficiency improvement control which can optimize both inverter and motor losses. A nonlinear power converter loss model is built to fit the nonlinear characteristics of power devices. This paper uses double Fourier integral analysis to analytically calculate the fundamental and harmonic components of motor current by which the fundamental motor loss and harmonic motor loss can be accurately analyzed. From these loss models, a whole-frequency-domain system loss model is derived and presented. Based on the system loss model, the system efficiency improvement control method applies the genetic algorithm to adjust the motor current and PWM frequency together to optimize the inverter and motor losses by which the system efficiency can be significantly improved without seriously influence on the system stability over the whole operation range of EVs. The optimal effects of system efficiency is verified by the experimental results in both Si-IGBT-based PMSM system and SiC-MOSFET-based system.

Radiation Damage in 4H-SiC and its Effect on Power Device Characteristics

The effect of neutron, electron and ion irradiation on electrical characteristics of unipolar 1700V SiC power devices (JBS diodes, JFETs and MESFETs) was investigated. DLTS investigation showed that above mentioned projectiles introduce similar deep acceptor levels (electron traps) in the SiC bandgap which compensate nitrogen shallow donors and cause majority carrier (electron) removal. The key degradation effect occurring in irradiated devices is the increase of the ON-state resistance which is caused by compensation of the low doped n-type epilayer and simultaneous lowering of electron mobility. In the case of SiC power switches (JFET, MOSFET), these effects are accompanied by the shift of the threshold voltage. Radiation defects introduced in SiC power devices is unstable and some defects anneal out already at operation temperatures (below 175°C). However, this does not have significant effect on device characteristics.

X-RAY TOPOGRAPHIC STUDY OF DEFECTS IN SI-BASED MULTILAYER EPITAXIAL POWER DEVICES

The defects in silicon based multilayer epitaxial structures intended for power epitaxial-diffusion devices as initial material were studied by x -ray topography techniques. It was shown the dislocation nets with non-uniform distribution of dislocations both over thickness and layer square in the form of dense rows (dislocation walls) or slip bands were principal defects in initial epitaxial layers and have influenced on electrical characteristics of power devices.

Mechanical Stress Dependence of Power Device Electrical Characteristics

This paper describes how mechanical stress affects the electrical characteristics of power devices, depending on the surface structure of the device and stress direction. We applied ideal external uni-axial stress to the various power devices, and studied the mechanism by comparing results from experiments and simulations. We found that the stress dependence of the on-state voltage mainly arose from the MOSFET portion of the IGBT. This consideration gives us the important information for designing a power module with higher output density.

Irradiation-Induced Deep Levels in Silicon for Power Device Tailoring

This paper gives an overview of the physics and electrical characteristics of irradiation-induced defects in silicon created by electrons, protons, and helium ions. The parameters of the traps usable as recombination centers or causing doping and discharging effects are described quantitatively, including temperature dependence and injection level dependence. The influence of recombination centers on the electric characteristics of power devices is discussed, especially with respect to applications for medium-voltage and high-voltage power devices.

On-line dead-time compensation method using disturbance observer

A new on-line dead-time compensation method for a permanent magnet (PM) synchronous motor drive is proposed. Using a simple disturbance observer without any additional circuit and off-line experimental measurement, disturbance voltages in the rotor reference dq frame caused by the dead time and nonideal switching characteristics of power devices are estimated in an on-line manner and fed to voltage references in order to compensate the dead-time effects. The proposed method is applied to a PM synchronous motor drive system and implemented by using software of a digital signal processor (DSP) TMS320C31. Simulations and experiments are carried out for this system and the results well demonstrate the effectiveness of the proposed method.

3.3 kV IGBT and diode chipset using lifetime control techniques and low-efficiency emitters

The adjustment of emitter efficiency by variation of doping profiles or application of lifetime control techniques such as irradiation of electrons and helium are two generally recognized concepts for the improvement of power device characteristics. In this work both concepts were studied by use of device simulation for the development of an IGBT and freewheeling diode chipset for 3.3 kV. Simulations were performed using an extended recombination model and recombination center data taken from measurements at different irradiated devices. Finally, this lead to the manufacturing of an IGBT using low-emitter efficiency and an irradiated freewheeling diode. The experimental results are in good accordance with the previously performed simulations and give evidence of the capabilities of present device simulation tools.

Comprehensive Study of the Electrothermal Operation of SiC Power Devices Using a Fully Coupled Physical Transport Model

ABSTRACTBased on an extended electrothermal drift-diffusion model formulated within the framework of phenomenological transport theory, a consistent set of material parameters for 4H- and 6H-SiC is presented. Furthermore we report on detailed numerical studies of the coupled effect between transient impurity kinetics and impact ionization, which alters the reverse blocking characteristics of power devices under short switching conditions.

Static and dynamic behavior of paralleled IGBTs

Problems associated with power device characteristics when power devices are connected in parallel, such as thermal stability and balanced switching behavior, can be solved by using insulated gate bipolar transistors (IGBTs). The author deals with parallel IGBT behaviors analyzing both static and dynamic characteristics. The influence of heatsink mounting, layout, and drive circuit are described in order to demonstrate the best way to make IGBTs parallel for optimum performance. In addition, the major advantages of the ISOTOP package are shown. >

The influence of doping inhomogeneities on the reverse characteristics of semiconductor power devices

Failure of the reverse characteristic of power devices may be caused by an increase of field strength due to doping inhomogeneities. A numerical program has been developed to calculate the effect of various types of perturbations on the maximum occurring field strength and on the shape of the space charge region. Three-dimensional calculations show that the influence of inhomogeneities can partly be compensated by the surrounding material. On the other hand, spikes of the diffusion front or p-islands with a high doping concentration inside the lowly doped n-region may cause an increase of field strength, which is not expected from the one-dimensional model.