Zhenxian Liang

Technology trends toward a system-in-a-module in power electronics

Currently, assemblies of power semiconductor switches and their associated drive circuitry are available in modules. From a few 100 watts downward, one finds silicon monolithic technology as the integration vehicle, while upward into the multi-kilowatt range, mixed mode module construction is used. This incorporates monolithic, hybrid, surface mount and wirebond technology. However, a close examination of the applications in motor drives and power supplies indicates that there has been no dramatic volume reduction of the subsystem. The power semiconductor modules have shrunk the power switching part of the converter, but the bulk of the subsystem volume still comprises the associated control, sensing, electromagnetic power passives and interconnect structures. The paper addresses the improvement of power processing technology through advanced integration of power electronics. The goal of a subsystem in a module necessitates this advanced integration. The central philosophy of this technology development research is to advance the state of the art by providing the concept of integrated power electronics modules (IPEMs). The technology underpinning such an IPEM approach is discussed. The fundamental functions in electronic power processing, the materials, processes and integration approaches and future concepts are explained.

Integrating active, passive and EMI-filter functions in power electronics systems:a case study of some technologies

Assemblies of power semiconductor switches and their associated drive circuits are at present available in modules. Upward into the multi-kilowatt range, mixed mode module construction is used. This incorporates monolithic, hybrid, surface mount, and wirebond technology. However, a close examination of the applications in motor drives and power supplies indicates that there has been no dramatic volume reduction of the subsystem. The power semiconductor modules have shrunk the power switching part of the converter, but the bulk of the subsystem volume still comprises the associated control, sensing, electromagnetic power passives (inductors, transformers, capacitors) and interconnects. This paper addresses the improvement of power processing technology through advanced integration of power electronics. The goal of a subsystem in a module necessitates this advanced integration, incorporating active switching stages, electromagnetic interference (EMI) filters, and electromagnetic power passives into modules by integration technology. The central philosophy of the technology development research in the National Science Foundation Engineering Research Center for Power Electronic Systems is to advance the state of the art by providing the concept of integrated power electronics modules (IPEMs) for all these functions. The technology underpinning such an IPEM approach is discussed.

Integrated CoolMOS FET/SiC-diode module for high performance power switching

A Si CoolMOS FET and SiC diode assembly with gate driver in boost configuration (ratings at 600 V/12 A), for power factor correction (PFC) application, has been fabricated in a version of IPEM - integrated power electronics module. It uses technology of so-called embedded power (EP), to form a three-dimensional (3-D) multiple chips/components interconnection with the capability of functional integration and high performance. An integrated power chip stage is built by embedding chips in a co-planar ceramic substrate and building up onto it a metallization thin-film interconnection. This deposited metallization not only bonds the power chips, but also provides the second-level interconnect wiring, so that associated components and base substrate are mounted from top and bottom sides. In this paper, the switching parameters of this module and their effects on a converters performance have been experimentally characterized. The procedures adopted for the defined fabrication processes of planar metallization interconnecting and solder stacking, are presented. In addition to the improvement of structural electrical properties, compared to a conventional discrete version, the characteristics of the planar process integration have also been demonstrated.

Integrated packaging of a 1 kW switching module using a novel planar integration technology

A metal-oxide-semiconductor field-effect transistor (MOSFET) (rating at 500 V/24 A) half-bridge power switching subassembly with gate drivers has been fabricated, employing a planar integration technology, in which an integrated power chips stage is built by embedding chips in a coplanar ceramic substrate with a metallization thin-film interconnection built up onto it. This deposited metallization not only bonds the power chips, but also provides the second-level interconnect wiring. The associated components are mounted on top of the integrated power stage. This packaging scheme results in a three-dimensional (3-D) multiple chips/components assembly with the capability of functional integration. In this paper, the electrical and thermal parameters of this packaged module have been experimentally and theoretically characterized. The procedures adopted for the defined fabrication processes are presented. In addition to the characteristics of the planar integration process, the improved electrical and thermal performance has been demonstrated.

A future approach to integration in power electronics systems

Assemblies of power semiconductor switches and their associated drive circuit are at present available in modules. Upward into the multi-kilowatt range, mixed mode module construction is used. This incorporates monolithic, hybrid, surface mount and wirebond technology. However, a close examination of the applications in motor drives and power supplies indicates that there has been no dramatic volume reduction of the subsystem. The power semiconductor modules have shrunk the power switching part of the converter, but the bulk of the subsystem volume still comprises the associated control, sensing, electromagnetic power passives (inductors, transformers, capacitors) and interconnects. This paper addresses the improvement of power processing technology through advanced integration of power electronics. The goal of a subsystem in a module necessitates this advanced integration, incorporating active switching stages, EMI-filters and electromagnetic power passives into modules. The central philosophy of the technology development research in the National Science Foundation Engineering Research Center for Power Electronic Systems is to advance the state of the art by providing the concept of integrated power electronics modules (IPEMs) for all these functions. The technology underpinning such an IPEM approach is discussed. The fundamental functions in electronic power processing, the materials, processes and integration approaches and future concepts are explained.

Development of Advanced All-SiC Power Modules

A thermally integrated packaging structure for an all silicon carbide (SiC) power module was used to realize highly efficient cooling of power semiconductor devices through direct bonding of the power stage and a cold baseplate. The prototype power modules composed of SiC metal-oxide-semiconductor field-effect transistors and Schottky barrier diodes demonstrate significant improvements such as low-power losses and low-thermal resistance. Direct comparisons to their silicon counterparts, which are composed of insulated gate bipolar transistors and PiN diodes, as well as conventional thermal packaging, were experimentally performed. The advantages of this SiC module in efficiency and power density for power electronics systems have also been identified, with clarification of the SiC attributes and packaging advancements.

Temperature-Dependent Short-Circuit Capability of Silicon Carbide Power MOSFETs

This paper presents a comprehensive short-circuit ruggedness evaluation and numerical investigation of up-to-date commercial silicon carbide (SiC) MOSFETs. The short-circuit capability of three types of commercial 1200-V SiC MOSFETs is tested under various conditions, with case temperatures from 25 to 200 °C and dc bus voltages from 400 to 750 V. It is found that the commercial SiC MOSFETs can withstand short-circuit current for only several microseconds with a dc bus voltage of 750 V and case temperature of 200 °C. The experimental short-circuit behaviors are compared, and analyzed through numerical thermal dynamic simulation. Specifically, an electrothermal model is built to estimate the device internal temperature distribution, considering the temperature-dependent thermal properties of SiC material. Based on the temperature information, a leakage current model is derived to calculate the main leakage current components (i.e., thermal, diffusion, and avalanche generation currents). Numerical results show that the short-circuit failure mechanisms of SiC MOSFETs can be thermal generation current induced thermal runaway or high-temperature-related gate oxide damage.

Methodology for switching characterization evaluation of wide band-gap devices in a phase-leg configuration

Double pulse tester (DPT) is a widely accepted method to evaluate the switching behavior of power devices. Considering the high switching-speed capability of wide band-gap (WBG) devices, the test results become significantly sensitive to the alignment of voltage and current (V-I) measurement. Also, because of the shoot-through current induced by Cdv/dt, during the switching transient of one device, the switching losses of its complementary device in the phase-leg is non-negligible. This paper summarizes the key issues of DPT, including layout design, measurement considerations, grounding effects and data processing. Among them, the latest probes for switching waveform measurement are compared, the methods of V-I alignment are discussed, and the impact of grounding effects induced by probes on switching waveforms are investigated. Also, for the WBG devices in a phase-leg configuration, a practical method is proposed for switching loss evaluation by calculating the difference between the input energy supplied by a dc capacitor and the output energy stored in a load inductor. Based on a phase-leg power module built with 1200 V SiC MOSFETs, the test results show that regardless of V-I timing alignment, this method can accurately indicate the switching losses of both the upper and lower switches by detecting only one switching current.

Reliability-oriented design considerations for high-power converter modules

In this paper, proper and detailed reliability models for the power converter are addressed to assess the reliability of the system, taking into account the effects of stresses and environment on the reliability of the components. Based on that, a system design strategy is proposed in two different ways, either through a system or components point of view. The former implies the minimization of the number of components, thus simplifying the converter structure, and the minimization of stress on the different devices and components. The latter pursues the employment of the best possible technology per available component. Finally, a reliability-oriented design for a three phase AC to DC, bidirectional power converter module is presented.

Embedded power technology for IPEMs packaging applications

Embedded power is a hybrid MCM-based 3-D integration packaging technology developed for integrated power electronics module application. Inside of the module the multiple bare power chips IGBTs or MOSFETs are buried in a ceramic frame and covered by dielectric with via holes on the Al pads of the chips. Then a deposited metallization interconnects the power devices and other electronics circuitry. Dielectric isolation pattern is fabricated using screen-printing approach. Multilayer metallization is deposited by sputtering and electroplating technologies. Two IPEMs have been fabricated to demonstrate the feasibility of this power electronics integration technology. Details of design and processing, as well as experiment results are presented.