Michael D. Glover

Wide Bandgap Technologies and Their Implications on Miniaturizing Power Electronic Systems

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.

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

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.

A 4H Silicon Carbide Gate Buffer for Integrated Power Systems

A gate buffer fabricated in a 2-μm 4H silicon carbide (SiC) process is presented. The circuit is composed of an input buffer stage with a push-pull output stage, and is fabricated using enhancement mode N-channel FETs in a process optimized for SiC power switching devices. Simulation and measurement results of the fabricated gate buffer are presented and compared for operation at various voltage supply levels, with a capacitive load of 2 nF. Details of the design including layout specifics, simulation results, and directions for future improvement of this buffer are presented. In addition, plans for its incorporation into an isolated high-side/low-side gate-driver architecture, fully integrated with power switching devices in a SiC process, are briefly discussed. This letter represents the first reported MOSFET-based gate buffer fabricated in 4H SiC.

Highly reliable nickel-tin transient liquid phase bonding technology for high temperature operational power electronics in electrified vehicles

This paper presents an approach to nickel-tin transient liquid phase (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 the packaging and bonding technology used. Transient liquid phase (TLP) bonding is one attachment approach that addresses these challenges. The Ni/Sn TLP bonding process exhibits a number of desirable characteristics, including a good CTE match with silicon and silicon carbide, popularity in conventional power electronics, low cost, and uniform alloy formation. The work herein presents a Ni/Sn TLP bonding technology (ready for high temperature operation up to 200°C) as applied to large size silicon power devices (12 mm × 9 mm). Analysis indicates that the resulting bondline is uniformly composed of Ni3Sn4 alloy throughout. This bonding approach has exhibited excellent reliability for bonded devices after 1000 thermal cycles from -40 to 200°C.

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

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.

Reliable and repeatable bonding technology for high temperature automotive power modules for electrified vehicles

This paper presents the feasibility of highly reliable and repeatable copper–tin transient liquid phase (Cu–Sn TLP) bonding as applied to die attachment in high temperature operational power modules. Electrified vehicles are attracting particular interest as eco-friendly vehicles, but their power modules are challenged because of increasing power densities which lead to high temperatures. Such high temperature operation addresses the importance of advanced bonding technology that is highly reliable (for high temperature operation) and repeatable (for fabrication of advanced structures). Cu–Sn TLP bonding is employed herein because of its high remelting temperature and desirable thermal and electrical conductivities. The bonding starts with a stack of Cu–Sn–Cu metal layers that eventually transforms to Cu–Sn alloys. As the alloys have melting temperatures (Cu3Sn: > 600 °C, Cu6Sn5: > 400 °C) significantly higher than the process temperature, the process can be repeated without damaging previously bonded layers. A Cu–Sn TLP bonding process was developed using thin Sn metal sheets inserted between copper layers on silicon die and direct bonded copper substrates, emulating the process used to construct automotive power modules. Bond quality is characterized using (1) proof-of-concept fabrication, (2) material identification using scanning electron microscopy and energy-dispersive x-ray spectroscopy analysis, and (3) optical analysis using optical microscopy and scanning acoustic microscope. The feasibility of multiple-sided Cu–Sn TLP bonding is demonstrated by the absence of bondline damage in multiple test samples fabricated with double- or four-sided bonding using the TLP bonding process.

A UVLO Circuit in SiC Compatible With Power MOSFET Integration

The design and test of the first undervoltage lock-out circuit implemented in a low-voltage 4H silicon carbide process capable of single-chip integration with power MOSFETs is presented. The lock-out circuit, a block of the protection circuitry of a single-chip gate driver topology designed for use in a plug-in hybrid vehicle charger, was demonstrated to have rise/fall times compatible with a MOSFET switching speed of 250 kHz while operating over the targeted operating temperature range between 0°C and 200°C. Captured data show the circuit to be functional over a temperature range from -55°C to 300°C. The design of the circuit and test results is presented.

High-Performance and High-Data-Rate Quasi-Coaxial LTCC Vertical Interconnect Transitions for Multichip Modules and System-on-Package Applications

A new design of stripline transition structures and flip-chip interconnects for high-speed digital communication systems implemented in low-temperature cofired ceramic (LTCC) substrates is presented. Simplified fabrication, suitability for LTCC machining, suitability for integration with other components, and connection to integrated stripline or microstrip interconnects for LTCC multichip modules and system on package make this approach well suited for miniaturized, advanced broadband, and highly integrated multichip ceramic modules. The transition provides excellent signal integrity at high-speed digital data rates up to 28 Gbits/s. Full-wave simulations and experimental results demonstrate a cost-effective solution for a wide frequency range from dc to 30 GHz and beyond. Signal integrity and high-speed digital data rate performances are verified through eye diagram and time-domain reflectometry and time-domain transmissometry measurements over a 10-cm long stripline.

Integration of Tantalum Pentoxide Capacitors With Through-Silicon Vias

Metal filled through-silicon vias (TSVs) allow devices to be connected using a 3-D approach. Optimizing and refining this technology has been a focus for the semiconductor industry the past few years because of the need for novel integrated circuit (IC) packages that address the issues associated with increased functionality and performance while reducing size and costs for a growing number of defense and consumer electronic applications. Vertical interconnection using TSV technology has emerged as a convenient way to improve system performance. Integration of decoupling capacitors with TSVs represents an attractive alternative to conventional 2-D layouts to achieve miniaturization and increased density. Decoupling capacitors can be brought in close proximity to the active elements, thereby reducing their parasitic inductance and allowing higher clock rates. In this paper, capacitors with anodized tantalum oxide dielectric were integrated with TSVs and their performance was evaluated. Fabricated capacitors were found to exhibit satisfactory electrical properties before and after TSV processing although some changes in their properties were observed. The performance of these capacitors for applications such as high speed decoupling capacitors was evaluated by measuring resonant frequency, parasitic inductance, and parasitic resistance.

The Design and Evaluation of an Integrated Wire-Bondless Power Module (IWPM) using Low Temperature Co-fired Ceramic Interposer

This article presents the plan and initial feasibility studies for an Integrated Wire Bond-less Power Module. Contemporary power modules are moving toward unprecedented levels of power density. The ball has been set rolling by a drastic reduction in the size of bare die power devices owing to the advent of wide bandgap semiconductors such as silicon carbide (SiC) and gallium nitride. SiC has capabilities of operating at much higher temperatures and faster switching speeds compared with its silicon counterparts, while being a fraction of their size. However, electronic packaging technology has not kept pace with these developments. High-performance packaging technologies do exist in isolation, but there has been limited success in integrating these disparate efforts into a single high-performance package of sufficient reliability. This article lays the foundation for an electronic package designed to completely leverage the benefits of SiC semiconductor technology, with a focus on high reliability and fast...