J. Y. Tsao,* S. Chowdhury, M. A. Hollis,* D. Jena, N. M. Johnson, K. A. Jones, R. J. Kaplar,* S. Rajan, C. G. Van de Walle, E. Bellotti, C. L. Chua, R. Collazo, M. E. Coltrin, J. A. Cooper, K. R. Evans, S. Graham, T. A. Grotjohn, E. R. Heller, M. Higashiwaki, M. S. Islam, P. W. Juodawlkis, M. A. Khan, A. D. Koehler, J. H. Leach, U. K. Mishra, R. J. Nemanich, R. C. N. Pilawa-Podgurski, J. B. Shealy, Z. Sitar, M. J. Tadjer, A. F. Witulski, M. Wraback, and J. A. Simmons

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Ultrawide-Bandgap Semiconductors: Research Opportunities and Challenges

In order to achieve lower fuel consumption and less greenhouse gas (GHG) emissions, we need higher efficiency vehicles with improved performance. Electrification is the most promising solution to enable a more sustainable and environmentally friendly transportation system. Electrified transportation vision includes utilizing more electrical energy to power traction and nontraction loads in the vehicle. In electrified powertrain applications, the efficiency of the electrical path, and the power and energy density of the components play important roles to improve the electric range of the vehicle to run the engine close to its peak efficiency point and to maintain lower energy consumption with less emissions. In general, the electrified powertrain architecture, design and control of the powertrain components, and software development are coupled to facilitate an efficient, high-performance, and reliable powertrain. In this paper, enabling technologies and solutions for the electrified transportation are discussed in terms of power electronics, electric machines, electrified powertrain architectures, energy storage systems (ESSs), and controls and software.

Making the Case for Electrified Transportation

This paper provides a comprehensive review and analyses on the state-of-the-art and future trends for high-power conductive on-board chargers (OBCs) for electric vehicles. To provide a global context, a summary of global charging standards and electric vehicle (EV) related trends are presented, which demonstrates momentum toward the OBCs with higher power rating. High-power OBCs are either unidirectional or bidirectional, and they have either an integrated or non-integrated system architecture. Non-integrated high-power OBCs are studied both from industry and academia, and the former are used to illustrate the current state of the art. The latter are classified on the basis of the converter design approach, studied for their principle of operation, and compared over power density, weight, efficiency, and other metrics. In addition to non-integrated OBCs, recent advancements in propulsion-machine integrated OBC solutions are also presented. Other integrated OBC techniques, such as system integration with the EV's auxiliary power module and wireless charging systems, are also discussed. Finally, future charging strategies and functionalities in charging infrastructures are addressed, and global OBC trends are summarized.

Global Trends in High-Power On-Board Chargers for Electric Vehicles

In order to take the full advantage of the high-temperature SiC and GaN operating devices, package materials able to withstand high-temperature storage and large thermal cycles have been investigated. The temperature under consideration here are higher than 200 °C. Such temperatures are required for several potential applications such as down-hole oil and gas industry for well logging, aircrafts, automotive, and space exploration. This review focuses on the reliability of a selection of potential components or materials used in the package assembly as the substrates, the die attaches, the interconnections, and the encapsulation materials. It reveals that, substrates with low coefficient of thermal expansion (CTE) conductors or with higher fracture resistant ceramics are potential candidates for high temperatures. Die attaches and interconnections reliable solutions are also available with the use of compatible metallization schemes. At this level, the reliability can also be improved by reducing the CTE mismatch between assembled materials. The encapsulation remains the most limiting packaging component since hard materials present thermomechanical reliability issues, while soft materials have low degradation temperatures. The review allows identifying reliable components and materials for high-temperature wide bandgap semiconductors and is expected to be very useful for researchers working for the development on high-temperature electronics.

Survey of High-Temperature Reliability of Power Electronics Packaging Components

The current state of wide bandgap device technology is reviewed and its impact on power electronic system miniaturization for a wide variety of voltage levels is described. A synopsis of recent complementary technological developments in passives, integrated driver, and protection circuitry and electronic packaging are described, followed by an outline of the applications that stand to be impacted. A glimpse into the future based on the current technological trends is offered.

Wide Bandgap Technologies and Their Implications on Miniaturizing Power Electronic Systems

This paper presents the concept, fabrication, and evaluation for quality and reliability of nickel-tin transient liquid phase (Ni-Sn TLP) bonding that provides high reliability for high-temperature operational power electronics in electrified vehicles The need for automotive power electronics to operate at high-temperature presents significant challenges in terms of packaging and bonding technology used TLP bonding is one attachment approach that addresses these challenges and facilitates high remelting temperatures while allowing processing to occur at relatively low temperatures and pressures In particular, the Ni-Sn TLP bonding process exhibits a number of desirable characteristics for power electronics, including popularity in conventional power electronics, low cost, and uniform and homogeneous alloy formation The work herein presents Ni-Sn TLP bonding (ready for high-temperature operation) as applied to silicon power devices of relatively large size (12 mm × 9 mm) The quality and reliability of the developed bonding process was characterized using material, optical, and electrical analysis Analysis indicates that the resulting bondline is uniformly composed of Ni3Sn4 alloy throughout the bond area This bonding approach has exhibited excellent reliability for bonded devices after thermal cycling from -40°C to 200°C Electrical properties of the bonded insulated gate bipolar transistor power devices demonstrated that Ni-Sn TLP bonding exhibits electrical performance comparable with conventional solder and is reliable at high-temperature operation

Nickel–Tin Transient Liquid Phase Bonding Toward High-Temperature Operational Power Electronics in Electrified Vehicles

This paper proposes a packaging method for SiC MOSFETs that provides a feasible solution of implementing press-pack packaging on SiC MOSFETs to extend the application of SiC devices into the high power range. The challenges in realizing press-pack packaging of SiC MOSFETs are addressed, and the solutions are proposed that fit the specific requirements of SiC MOSFET. To achieve pressure contact on SiC MOSFETs, miniature and flexible press pins called “fuzz buttons” are used in a low-profile interposer to realize die top side connection. Since the press-pack does not provide internal insulation between the active device and the heatsink, the heatsink is included in the power loop. To avoid large parasitic loop inductance being introduced by the heatsinks, a microchannel heatsink is developed which has a low thickness while remaining adequate heat dissipation efficiency. The structure and assembly process flow of the press-pack SiC MOSFET are provided. A half-bridge stack prototype with two press-packs and three heatsinks is developed. The thermal and electrical performances of the press-pack and the half-bridge stack are evaluated by simulations and tests to validate the feasibility of the proposed packaging approach.

A Solution to Press-Pack Packaging of SiC MOSFETS

This paper presents a three-dimensional (3-D) wire bondless power module using silicon carbide (SiC) power devices. Commercially available SiC power devices are designed for wire bonding. Wire bonds have an inherent parasitic inductance that limits high-frequency switching. This results in an underutilization of the full potential of SiC power devices, which have very low switching losses at high frequencies. Wire-bonded power modules run into a performance ceiling when it comes to ultrafast switching. This paper strives to provide a solution to this issue, which involves reconfiguring a commercially available bare die SiC power device into a flip-chip-capable device. A wire bondless SiC Schottky diode package was demonstrated and its performance was contrasted with a conventional wire-bonded package. A 24% reduction in the ON-state resistance was observed in the wire bondless package. As a next step, wire bondless SiC MOSFET packages were developed and tested in a half-bridge configuration in a highly integrated 3-D arrangement. This approach departs from the conventional concept of a power module—demonstrating a direct-bonded-copper-less and baseplate-less half-bridge switching cell. Double-pulse tests conducted on the cell showed >3× reduction in the parasitic inductance of the 3-D cell as compared with a conventional wire-bonded module.

3-D Wire Bondless Switching Cell Using Flip-Chip-Bonded Silicon Carbide Power Devices

Limitations of silicon (Si) based power electronic devices can be overcome with Silicon Carbide (SiC) because of its remarkable material properties. SiC is a wide bandgap semiconductor material with larger bandgap, lower leakage currents, higher breakdown electric field, and higher thermal conductivity, which promotes higher switching frequencies for high power applications, higher temperature operation, and results in higher power density devices relative to Si [1]. The proposed work is focused on design of a SiC gate driver to drive a SiC power MOSFET, on a Cree SiC process, with rise/fall times (less than 100 ns) suitable for 500 kHz to 1 MHz switching frequency applications. A process optimized gate driver topology design which is significantly different from generic Si circuit design is proposed. The ultimate goal of the project is to integrate this gate driver into a Toyota Prius plug-in hybrid electric vehicle (PHEV) charger module. The application of this high frequency charger will result in lighter, smaller, cheaper, and a more efficient power electronics system.

Michael D. Glover

Papers

Wide Bandgap Technologies and Their Implications on Miniaturizing Power Electronic Systems

Nickel–Tin Transient Liquid Phase Bonding Toward High-Temperature Operational Power Electronics in Electrified Vehicles

A Solution to Press-Pack Packaging of SiC MOSFETS

3-D Wire Bondless Switching Cell Using Flip-Chip-Bonded Silicon Carbide Power Devices

A wide bandgap silicon carbide (SiC) gate driver for high-temperature and high-voltage applications