Lightweight, Cost-Effective Power Modules Using Polymer Baseplates With Integrated Microconvective Cooling

Due to their superior material properties, wide bandgap (WBG) semiconductors enable the application of power electronics at higher temperature operation, higher frequencies, and higher efficiencies compared to silicon (Si). However, the commonly-used aluminum wire bonding as topside interconnection technology prevents WBG semiconductors from reaching their full potential, due to inherent parasitic inductances, large size, heat dissipation, and reliability issues of wire bonding technology. Therefore, this article presents a comprehensive review of topside interconnection technologies of WBG semiconductor power devices and modules. First, the challenges and driving factors for the interconnection of WBG semiconductor dies are discussed. Second, for each widely commercially used WBG semiconductor, i.e., silicon carbide and gallium nitride, technical details and innovative features of state-of-the-art interconnection techniques in packages are reviewed. Then, the majority of existing topside interconnection materials for WBG semiconductors are categorized and compared, followed by a discussion of their advantages, challenges, and failure modes. Based on this elaborate discussion, potential future directions of the interconnection technology development are given. It is concluded that the superior performance of WBG semiconductors can be obtained by combining novel materials with innovative designs for the topside interconnections.

III-Nitrides promise to offer high-frequency power amplifiers at higher power densities. This is attractive for realizing device platforms for 5G and beyond. It also enables integrating Si-based electronics to complement functionalities. However, to obtain the full potential of III-Nitrides one must operate these transistors at higher power densities, for which thermal management is crucial.Due to the continuous need for higher performance in various applications ranging from DC to W-band frequencies, semiconductor devices are pushed to higher power densities. This results in a higher junction temperature owing to the Joule heating in the channel resulting in device performance degradation and premature failure. Using devices based on wide-bandgap (WBG) semiconductors such as Gallium Nitride (GaN) and Gallium Oxide (GaOx) with a larger critical electric field and high-temperature tolerance, one could increase the power density. However, in order to increase the output power to the levels that is promised by these wide bandgap materials, junction temperature reduction through device-level cooling is critical. We are actively researching thermal management at device, circuit and packaging level using synthetic polycrystalline (PC) diamond. PC-diamond, at an appropriate grain size offers a TC is higher than any competing thermal vias with metals without interfering the electrical performance. Over the past 5 years we have demonstrated the potential of integrating diamond with GaN and recently achieving a record low diamond/GaN thermal boundary resistance (TBR) along with a relatively high diamond thermal conductivity (TC). This remarkable thermal performance was be achieved by maintaining the electrical performance, as demonstrated by the unharmed channel charge and mobility results.There are two key requirements for thermal management using heat spreading from the channel: first, a low thermal boundary resistance (TBR) between the hot spot in the channel and the heat spreader is required (in this study between GaN channel and diamond). Second, a low thermal resistance path to the heat-sink is crucial from the diamond layer which is directly proportional to diamond’s thermal conductivity (TC). In collaboration with Univ of Bristol, we have reported a TBR of ~3 m2K/GW, to date, known to be the lowest reported TBR for GaN HEMT technology. Diamond-GaN TBR depends strongly on the interface smoothness and the thickness of interfacial Si3N4 layer. A thinner Si3N4 resulted in lower TBR and allowed superior phonon coupling from the channel to the spreader. We have also measured a remarkably high TC for a 2 μm-thick diamond layer yielding over 650 W/m.K. The diamond grains are near isotropic in shape that allows excellent in-plane and cross-plane thermal conductivity. Achieving high TC within a thin film of diamond, grown heterogeneously, underscores the importance of our technique, since it reduces the residual stress when integrating with different materials that involves many thin layers like GaN/AlGaN HEMT epi-layers.β-Ga2O3 is an emerging ultra-wide bandgap material showing promises for both power and RF devices. However, the material’s low thermal conductivity poses to be a challenge for efficient power delivery (at any frequencies). PC diamond was successfully grown on (‾¯201)β-Ga2O3 using proper nucleation technique and thermal characterizations were conducted. A thermal conductivity (diamond + nucleation) and thermal boundary resistance at the diamond/β-Ga2O3 interface of 110 ± 33 W/mK and 30.2 ± 1.8 m2K/GW, respectively were measured.Our current results demonstrates a very promising roadmap for wide bandgap semiconductors via diamond integration.

The expansion of the electric vehicle market is driving the request for efficient and reliable power electronic systems for electric energy conversion and processing. The efficiency, size, and cost of a power system is strongly related to the performance of power semiconductor devices, where massive industrial investments and intense research efforts are being devoted to new wide bandgap (WBG) semiconductors, such as silicon carbide (SiC) and gallium nitride (GaN). The electrical and thermal properties of SiC and GaN enable the fabrication of semiconductor power devices with performance well beyond the limits of silicon. However, a massive migration of the power electronics industry towards WBG materials can be obtained only once the corresponding fabrication technology reaches a sufficient maturity and a competitive cost. In this paper, we present a perspective of power electronics based on WBG semiconductors, from fundamental material characteristics of SiC and GaN to their potential impacts on the power semiconductor device market. Some application cases are also presented, with specific benchmarks against a corresponding implementation realized with silicon devices, focusing on both achievable performance and system cost.

Wide band gap (WBG) semiconductors, such as gallium nitride (GaN), have become popular among switching power modules. In pursuing power conversion efficiency, power module's high-speed and high-power operation leads to electromagnetic (EM) noise in a very wide frequency range, potentially interfering with nearby wireless communications [e.g., long-term evolution (LTE)]. This letter analyzes the source of EM noise from the power modules using GaN transistors in half-bridge circuits. EM noise was clearly observed in the proximity of power modules and attributed to two primary sources in the frequency range of interest up to 6 GHz: 1) the periodical switching operation of GaN transistors in the output stage and 2) the logic operation of complementary metal–oxide–semiconductor digital circuits to control gate drivers, in the lower and upper side of frequencies, respectively. Measurements analyzed the EM noise characteristics at different probing locations over the assembly of two GaN power modules as well as in different operating conditions by strategically supplying source signals. The influence of EM noise on LTE receiver performance is evaluated with wireless system-level simulation and related to the degradation of its minimum receivable input power.

Devices based on wide bandgap (WBG) semiconductors like silicon carbide (SiC), gallium nitride (GaN), and gallium oxide (Ga2O3) are ideal for high-power electronics in harsh environments. Among the WBG semiconductors, ultrawide bandgap (UWBG) β-phase gallium oxide (Ga2O3), EG ≈ 4.8 eV, is emerging as a replacement for the current commercially available wide bandgap (WBG) power electronics due to its generational improvements in performance and manufacturing cost [1]. Ga2O3 has a high theoretical breakdown electrical field of 8 MV/cm which in turn gives its Baliga’s figure of merit for power devices that is larger than other WBG materials. The availability of high-quality Ga2O3 substrates produced from melt-grown bulk single crystals also facilitates the development of vertical power devices.In the current stage, the vertical Schottky barrier diode (SBD) with Ga2O3 can have an improved current spreading effect when compared to power diode devices from Si, SiC, and GaN. Especially, the Ga2O3 is expected to surpass the trade-off relationship between breakdown voltage (BV) and on resistance (Ron,sp) that other materials have [2]. Nevertheless, the Ga2O3 vertical SBD still cannot achieve the theoretical breakdown electric field. One of the key topics for WBG semiconductors application is a structure for improved electrical management such as field rings, junction termination extension, and field plates to reduce the leakage current in the reverse bias state.Here, we investigate the characteristics of Ga2O3 SBDs with and without mesa structure in extreme environments at high and low temperature. Conventional and mesa Ga2O3 SBDs were fabricated on the halide vapor phase epitaxy (HVPE) grown β-Ga2O3 (001). A Sn-doped substrate with 61016 cm-3 was used for the HVPE growth. In the SBD with mesa structure, the circular mesa with a diameter of 162 μm and a depth of 500 nm was formed around anode electrodes. The Ti/Au metal stack on the back side of the substrate acted as a cathode and the anode electrode deposited Ni/Au/Pt layers. After the fabrication process, current-voltage (I-V) measurements were performed on the SBDs between -5 V and 1 V. From the results, the values of Ron,sp at 0.7 V are 46.4 Ω•cm2 and 46.2 Ω•cm2 in conventional and mesa SBDs, respectively. And additionally, the leakage current at -5 V is reduced by approximately 44.3% in the mesa structure. To obtain the Schottky barrier height (SBH) from I-V and capacitance-voltage (C-V) measurements, the C-V was observed in the range of -5 V to 0.5 V at 100 kHz. The SBH values from I-V and C-V measurements, the mesa SBDs have 1% - 5% larger SBH compared to the conventional structure, and it could be related to lower leakage current. Moreover, the depletion depths of conventional and mesa SBDs were 52.2 nm and 57.8 nm, respectively, from C-V measurements. For considering the electrical characteristics in extreme temperatures, the I-V measurements of both SBDs structure will be measured between 75 K to 525 K. From an initial low temperature measurement series, we determine a Richardson constant of 49 A/cm2 comparable to what has been reported by other groups. Furthermore, we will extend the study by performing deep-level transient spectroscopy (DLTS) to understand the defect information in Ga2O3.

During the last few decades, the microelectronics packaging industry has moved into the 2.5D to 3D space for increased density, functionality, and speed. Similar concepts and ideas for developing 2.5D to 3D power electronics packaging are desired to achieve even greater efficiency and power density over conventional power electronics packaging methods. Wide-band gap (WBG) semiconductors, such as SiC and GaN, have accelerated the ability to shrink the volumetric size and weight of these power conversion systems, and thus improve overall power density metrics, due to their inherent high frequency, high temperature, and high voltage capabilities. WBG power semiconductor devices, with these attributes, thus make themselves excellent candidates for more aggressive packaging, compared to Si-derived packaging, in order to not only take full advantage of the WBG device ratings, but also to achieve high power densities of the overall power conversion systems. Already different/multiple power semiconductor devices are being combined by processing them together on the same die to boost electrical performance and increase power density. It can be assumed that further levels of integration will be sought after for the next levels of packaging to enable similar gains, especially with the advent of double side solderable die. The 3D stacking of die, components, and substrates creates the question of how well will each of these perform in close proximity to each other. This work focuses on the numerical simulation and experimental measurements to predict the temperature distribution of power converters built in a stacked fashion. Thermal models of a stacked power electronic switching unit — a silicon controlled rectifier and anti-parallel diode — are modeled under the assumption of equally sized die. Temperature field maps are generated for 20W to 250W of power dissipations across the power semiconductor die. Thermal models are then compared with matching experimental setups to observe the effect of switching unit placement attached to a given substrate on the die junction temperatures for various scenarios of thermal crosstalk. Results from this work are expected to aid in the development 2.5D to 3D power electronic packaging by predicting thermal performance of stacked, ultra-dense, WBG device -based packages.

Wide bandgap semiconductors such as SiC and GaN have superb properties in breakdown strength, temperature resistance, and efficiency. Due to the widespread use of wide bandgap devices, the power density is required to be as high as possible and the key approach is to increase the working voltage and decrease the packaging size. The packaging insulation of high-voltage power modules such as SiC MOSFET should withstand high multi-physics stress and guarantee reliability. The electric field distribution is highly related to the electrical conductivity of packaging insulation since the electric stress in the packaging insulation is either constant DC voltage or unipolar square wave voltage due to the intrinsic body diode of SiC MOSFET. However, the non-linear conductivity and its coupling relationship with the electric field and temperature have not been investigated before. In this paper, a multi-physics analysis of electric field and temperature in high-voltage SiC MOSFET power modules is proposed. The non-linear electrical conductivity of packaging insulation materials (encapsulation and substrate ceramic) is measured and analyzed to derive an expression. Then a half-bridge SiC MOSFET is modeled in multi-physics software and the non-linear conductivity is considered to simulate the transient distribution of electric field and temperature in the packaging, especially at the key triple point positions. To use the multi-physics in the packaging insulation, an optimization procedure is proposed for future high-voltage power module design and fabrication.

This paper presents the development of a power electronics teaching lab to prepare students for the next generation of power electronics engineering using wide bandgap (WBG) semiconductor devices. The objectives are to expedite the transfer of theoretical knowledge to practical experience on WBG semiconductor devices, and at the same time to provide a hands-on understanding of the development of comprehensive power electronics systems. To incorporate different types of semiconductor devices, especially WBG semiconductor switches, and perform various lab experiments from an investigation of component switching characteristics to construction and operation of power converters, a plug-and-play (P&P) modular power electronics education board is developed. The P&P architecture allows easy construction of different power electronics circuits by simply inserting semiconductor daughter boards to the motherboard. To assist students’ learning experience, the lab curriculum consisting of lab manuals and supporting resources is developed. Multiple workshops have been held with ECE undergraduate and graduate students to evaluate the performance of the lab. Final assessment and student’s feedback are presented as the outcome of the development.

Recent advances in wide band-gap (WBG) semiconductor materials, such as silicon carbide (SiC) and gallium nitride (GaN) are enabling a new generation of power semiconductor devices that far exceed the performance of silicon-based devices. Past ARPA-E programs (ADEPT, Solar ADEPT, and SWITCHES) have enabled innovations throughout the power electronics value chain, especially in the area of WBG semiconductors. The two recently launched programs by ARPA-E (CIRCUITS and PNDIODES) continue to investigate the use of WBG semiconductors in power electronics. From materials and devices to modules and circuits to application-ready systems integration, ARPA-E projects have demonstrated the potential of WBG semiconductors to lower the cost of high-efficiency power electronics to enable broad adoption in energy applications.

Wide bandgap (WBG) semiconductors such as silicon carbide (SiC) and gallium nitride (GaN) offer higher switching speed, greater power density, and elevated operational temperature capabilities compared to silicon-based counterparts. However, conventional packaging technologies cannot fully leverage these benefits, necessitating innovative packaging strategies. This dissertation explores pressure contact technology (PCT) to enhance performance and reliability of highly integrated WBG power modules. Various interconnection approaches are evaluated for their suitability: fuzz buttons provide low parasitic inductance and flexibility for gate connections; graphene film (GF) elastomers offer compact size and high thermal conductivity; and metal sheet springs ensure robust power interconnections. A novel spring connector with low inductance (3 nH) and electrical resistance (5 mΩ) is utilized to connect substrates, enhancing heat dissipation and mechanical stability. The electro-thermal characteristics and reliability of pressure contact with molybdenum plates (PCMo) technology are compared with emerging die-attach technologies such as pressureless sintered Ag (SAg), pressure sintered Cu (PSCu), and commercial TO220 counterparts incorporating the same SiC chips. Experimental results demonstrate that PCMo introduces additional contact resistance (∼ 10 mΩ, 0.42 K/W) but exhibits superior power cycling reliability (∼ 6053 cycles) under a junction temperature from 50ºC to 200ºC due to the elimination of die-attach failures. Failure analysis identifies degradation and crack mechanisms in SAg, PSCu, and TO220 samples. Building on these insights, a 3D PCT-based half-bridge SiC module is developed using GF and fuzz buttons, achieving a low thermal resistance of 0.66 K/W, minimal parasitic inductance of 5.1 nH, and reduced voltage overshoot of 5.8%. For high-power applications, an eight-chip parallel SiC module with metal sheet springs demonstrates balanced current distribution and low inductance of 4.8 nH. The findings of this dissertation highlight the potential of PCT in improving the performance and reliability of heterogeneous integrated WBG power modules, particularly for high-power and high-temperature applications.

Increasing the efficiency and the reliability of converters are the main goals in power electronics. This research contributes to these goals by investigating how to integrate nonintrusive current measurement into Gallium Nitride (GaN) power modules. Therefore, Finite Element Analysis (FEA) simulations are conducted to determine the location of the sensor as well as the power electronic layout and the AC capacitor placement. These simulations and the experience gathered while working with a synchronous GaN buck converter and an anisotropic magnetoresistive (AMR) sensor board lead finally to the design of the GaN power module, which is presented in this article. The novel outcome of this project is the current sensing unit included in the power module. Based on the simulation results, it was decided to measure the current mismatch between the two parallel GaN switches for reliability assurance and circuit protection. Moreover, the sensor choice is discussed and experimental measurements with the board are presented.

Wide band-gap (WBG) semiconductors technology represents a potential candidate to displace conventional silicon (Si) technology used in power electronics. Between Silicon Carbide (SiC) and Gallium Nitride (GaN) power semiconductors, the latter is the least mature of both technologies, with many open research problems, especially in the aerospace industry. In this paper, we address the design and implementation of a DC/DC converter for a hybrid small unmanned aerial vehicle (UAV) based on GaN technology. Both theoretical and simulation comparisons of Si, SiC and GaN transistors for the converter are presented. The conclusion is that GaN devices are the most appropriate to fulfill converter requirements for the size and weight limitations of the selected UAV. The paper presents a buck converter which handles an input voltage range of 32 V to 40 V and provides a 12 V regulated output and output power up to 60 W. The experimental results carried out on the prototype converter show how promising the GaN technology is for aerospace systems, not only regarding its volume and size, but also its efficiency. Besides, practical implementation details are reported to contribute to the design of small, light and reliable GaN power converters for aeronautics.

A Busy March Meeting Is Brewing in Seattle

The research presented in this thesis was carried out in VISHAY Semiconductor Italiana S.P.A. at Borgaro Torinese - Italy. The framework of this thesis is the study of new materials for power electronics application, analysing their thermal, mechanical and electrical properties. Emerging application of high power systems requires new methods for power electronics integration and packaging. Stringent requirements in size and weight, reliability, durability, ambient and operation temperatures are pushing to go beyond the limits in industrial applications. As a consequence, our studies are focused on power modules, incorporating new materials and technology processes (sintering) for dies or chips (silicon), substrates and interconnection materials (wire bonding). This thesis work starts introducing the power semiconductor devices used in power electronics and their integration on Power Integrated Circuits (low and medium power density) and Power Modules (medium, high and very high power density). This chapter will explain technology evolution, power semiconductor device utilization mode and some applications. Chapter 2 will be focused on power modules packages. They have an important role for providing cooling, electrical connection and correct insulation, between the internal semiconductor devices and the external circuit. Isolated and non isolated packages are analysed and compared. Chapter 3 will make a point on the methods of thermal characterization and reliability tests, that were implemented to evaluate the impact of the introduction of new materials and processes into the device. In chapter 4, first experimental results, related to the sintering process will be discussed. In this chapter the attention will be focused on the Chip to substrate Joint of the device, analysing methods to mechanically fix die to substrate. The sintering process will be treated, analysing the process and the results will be thermally and mechanically characterized. The chapter 5 will present the experimental part oriented to the combinations of materials to produce a better heavy wire bonding, supported by a Design of Experiments (DOE). The behaviour of didifferent wires will be compared through thermal characterization methods and reliability test

High-electron-mobility transistors (HEMTs) based on wide bandgap (WBG) materials like gallium nitride (GaN) are vital for next-generation power electronics and high-frequency applications, offering high breakdown voltage, electron mobility, and power density. The global shift toward electrification and sustainability is driving demand for GaN and silicon carbide (SiC) power devices. However, challenges such as current collapse and increased channel resistance under high-power conditions hinder performance. To address these limitations, numerous solutions have been explored, with simulation emerging as an indispensable starting point. Technology Computer-Aided Design (TCAD) simulations play a critical role by enabling accurate modeling, performance optimization, and reduced experimental effort. This paper reviews key and advanced physical models in TCAD simulations of GaN HEMTs, covering mechanisms such as carrier transport, thermal effects, and impact ionization. Mobility models-FLDMOB, Albrecht, Gansat, Yamaguchi, Brooks-Herring, and Conwell-Weisskopf-are analyzed for capturing velocity saturation and nonlocal transport. Recombination models like Shockley-Read-Hall and Auger are discussed in relation to carrier lifetime, while impact ionization models, including van-Overstraeten-de-Man, Selberherr, and Okuto-Crowell, are evaluated for breakdown prediction. Emphasis is placed on choosing models suited to specific structures and conditions to ensure simulation accuracy. Advanced modeling enhances TCAD's predictive power, supporting innovation in GaN-based power electronics.